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Sertraline Hydrochloride
SERTRALINEHYDROCHLORIDE
Bruce M. Johnson and Pei-Tei L. Chang
Central Research Pfizer Inc Groton, CT 06340
ANALYTICAL PROFILES OF DRUG SUBSTANCES AND EXCIPIENTS-VOLUME 24
443
Copyright 0 1996 by Academic Press, Inc. All rights of reproductionin any form reserved.
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BRUCE M. JOHNSON AND PEI-TEI L. CHANG
SERTRALXNE HYDROCHLORIDE 1. Introduction 2. Description 2.1. Structural Formula 2.2. Molecular Formula and Molecular Weight 2.3. Nomenclature 2.4. Laboratory Codes 3. Synthesis 4. Physico-Chemical Properties 4.1. Appearance, Color, Odor 4.2. Melting range 4.3. Solubility 4.4. Hygroscopicity 4.5. Ultraviolet Spectra 4.6. Infrared Spectra 4.7. Proton Nuclear Magnetic Resonance Spectra 4.8. Carbon- 13 Nuclear Magnetic Resonance Spectra 4.9. Mass Spectra 4.10. Optical Rotation 4.11. pH andpKa 4.12. Single Crystal X-Ray 4.1 3. Polymorphism 5. Methods of Analysis 5.1. Elemental Analysis 5.2, Ionic Chlorine 5.3. Identification 5.4. Thin Layer Chromatography 5.5, Ultraviolet Spectroscopy 5.6. Potentiometric Titration 5.7. High Performance Liquid Chromatography 5.8. Gas Liquid Chromatography 5.9. Biological Fluids 6 . Stability 7. Pharmacokinetics and Metabolism 7.1. Systemic Bioavailability 7.2. Metabolism
SERTRALINE HYDROCHLORIDE
1.
445
introduction Sertraline hydrochloride is an antidepressant for oral administration. It is chemically unrelated to tricyclic, tetracyclic, or other available antidepressant agents. It is a novel inhibitor of serotonin reuptake in the brain'. The mechanism of action of sertraline is presumed to be linked to its inhibition of CNS neuronal uptake of serotonin (5HT).Studies at clinically relevant doses in man have demonstrated that sertraline blocks the uptake of serotonin into human platelets. Studies in animals also suggest that sertraline is a potent and selective inhibitor of neuronal serotonin reuptake and has only very weak effects on norepinephrine and dopamine neuronal reuptake. In vifrostudies have shown that sertraline has no significant affinity for adrenergic (alpha 1, alpha 2, beta), cholinergic, GABA, dopaminergic, histaminergic, and serotonergic (5HT1A, SHTlB, 5HT2)or benzodiazepine receptors; antagonism of such receptors has been hypothesized to be associated with various anticholinergic, sedative, and cardiovascular effects for other psychotropic drugs. The chronic administration of sertraline was found in animals to downregulate brain norepinephrine receptors, as has been observed with other clinically effective antidepressants. Sertraline does not inhibit monoamine oxidase.*
2.
Description
2.1.
Structural Formula
Sertraline is the S-cis enantiomer of a disubstituted tetrahydronaphthalene. The structural formula of sertraline hydrochloride is given below:
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BRUCE M. JOHNSON AND PEI-TEI L. CHANG
H-N-CH,
I
mHCI
Cl
Sertraline Hydrochloride 2.2.
2.3.
Molecular Formula and Molecular Weight Molecular Formula
Sertraline
c1 7H 17Nc12
Molecular Weight 306.2
Sertraline hydrochloride
Cl7H@C13
342.7
Nomenclature
Chemical Names: 1. ( 1S-cis)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-Nmethyl-1-naphthalenaminehydrochloride (CAS-79559-97-0) Preferred use name.
2. cis-( lS,4S)-N-rnethyl-4-(3,4-dichlorophenyl)-1,2,3,4tetrahydro- 1-naphthalenamine hydrochloride (J. Med. Chern. 1984, 27(11), 1508) 3. cis-( 1S)-N-methyl-4-(3,4-dichlorophenyl)-1,2,3,4tetrahydro- 1-naphthalenamine hydrochloride (US Patent 4,536318)
SERTRALINE HYDROCHLORIDE
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4. 1-naphthalenamine,4-(3,4-dichlorophenyl)-1,2,3,4tetrahydro-N-methyl, hydrochloride, ( 1S-cis)- (USAN chemical name 1) 5. (lS,4S)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-Nmethyl- 1-naphthylamine hydrochloride (USAN chemical name 2)
2.4.
B.A.N.:
Sertraline hydrochloride
U.S. A.N. :
Sertraline hydrochloride
I.N.N.:
Sertraline hydrochloride
Proprietary or Trade Name:
Zolofim (USA) LustralTM(UK)
Laboratory Codes Sertraline has the Pfizer code CP-5 1,974 Sertraline hydrochloride has the Pfizer code CP-5 1,974-01
Synthesis The pure drug substance is manufactured from commonly available intermediates using a four step process. The structurally significant starting material is 4-(3,4-dichlorophenyl)-3,4-dihydro-1(2H)n a p h t h a l e n ~ n e which ~ s ~ ~is~reacted ~ ~ ~ ~with ~ methylamine to form the imine. The imine, (N-[4-(3,4-dichlorophenyl)-3,4-dihydro1(2H)-naphthalenylidenelmethanamine), is reduced by catalytic hydrogenation to a pair of racemic diastereomers. The racemic cis isomers are separated from the racemic trans isomers by selective crystallization of the hydrochloride salts. The racemic cis enantiomers are then resolved with D(-)-mandelic acid. In the final step the mandelate counterion is replaced by chloride to give the finished drug substance, sertraline hydrochloride.’* lo Crystallization conditions in the final step determine the polymorphic form produced.
BRUCE M.JOHNSON AND PEI-TEI L. CHANG
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4.
Physico-Chemical Properties
4.1.
Appearance, Color, Odor
Sertraline hydrochloride is a white to off-white, crystalline powder having no odor. It is an irritant, contact with skin and eyes should be avoided.
4.2.
Melting range
Determination of the melting point by the capillary method in a Buchi 510 melting point apparatus with a heating rate of 1°C per minute on Form I shows the onset of change at about 160 to 180°C with movement of the sample and a slight color change. At about 218°C a partial melt is observed but the sample does not become clear until a temperature of 245 to 250°C is reached. This is consistent with the DSC and hot stage microscopic observations.
4.3.
Solubility
4.3.1. Aqueous Solubility The solubility of a saturated solution of sertraline hydrochloride (Form I) in distilled water at room temperature is 3.8 mg/mL. The pH of this saturated solution is 5.3. Solubility in water is pH dependent, as the data in the following table shows. These data were determined by preparing a saturated solution in distilled water, with pH adjustments made by addition of sodium hydroxide and/or hydrochloric acid, followed by appropriate filtering, diluting, and assay by HPLC.
SERTRALINE HYDROCHLORIDE
DH
1 .o 2.0 2.9 4.2 6.0 6.2 6.3 6.5 7.2 7.7 8.8 9.8 10.2 11.1 12.1
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Solubility (mg/mL) 0.89 2.98 3.88 4.07 4.46 4.93 4.93 3.32 0.72 0.21 0.02 0.006
0.004
0.004 CO.004
4.3.2. Solubility in Other Solvents The approximate solubility of sertraline hydrochloride in selected solvents at room temperature is given below. These data were obtained at room temperature, with saturated solutions that were appropriately filtered, diluted, and assayed by HPLC. Solvent Aqueous 0.1 N HC1 Aqueous 0.1 N NaOH Ethanol Isopropyl alcohol Chloroform Acetone N,N-dimethy1formamide Dimethylsulfoxide Ethyl acetate Acetonitrile Methanolic 0.1 N HC1 Chloroform/methanol, 1: 1
Solubility (mg/mL,) 0.5 1 0.002 15.7 4.3 110 1.1 88 147 0.20 0.85 47 134
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4.4.
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
Hygroscopicity
The hygroscopicity of sertraline hydrochloride (Form I) was determined by exposing a sample for one week to an atmosphere of 37"C/75% relative humidity, and a sample to room temperature/88% relative humidity. Karl Fischer titration was used to determine water content. The results showed water contents of
4.5.
Ultraviolet Spectra
The ultraviolet absorption spectra of sertraline hydrochloride were recorded in methanol, methanolic 0.01 N hydrochloric acid, and methanolic 0.01 N sodium hydroxide. These spectra are presented as Figures 1,2, and 3. below:
Absorptivity data for sertraline hydrochloride are given
265 273 28 1
Absorptivity 2.58 3.04 1.64
Methanol
265 273 28 1
2.61 3.06 1.64
0.01 N NaOWMethanol
265 273 28 1
1.92 2.26 1.60
Solvent 0.01 N HCYMethanol
&-nm
SERTRALINE HYDROCHLORIDE
45 1
The table below demonstrates that the absorptivity and hremain effectively unchanged in solutions of differing acid strengths. Acid Strength 0.005 N 0.01 N 0.05 N 0.10 N 0.50 N
Lax
273 273 273 273 273
Absorptivity 3.03 3.04 3.1 1 3.03 3.04
Sertraline hydrochloride also adheres to Beer's Law at this wavelength, as evidenced by the following data: Concentration (mg/mL) 0.101 0.201 0.302 0.402 0.503 0.603 0.704 0.804 0.905 1.01 avg. k std. dev.
Lax 273 273 273 273 273 273 273 273 273 273
Absorptivity 2.99 2.97 3.04 2.99 2.99 3.01 2.96 2.97 2.95 2.88 2.98 f 0.04
BRUCE M.JOHNSON AND PEI-TEI L.CHANG
452
A b S
0
r
b a
n C
e
Figure 1. Ultraviolet Spectrum of Sertraline HC1 in Methanol
i
2.0
A b S 0
r
b a
n C
Wawkngth (nm)
Figure 2. Ultraviolet Spectrum of Sertraline HCl in Methanolic HCl
SERTRALINEHYDROCHLORIDE
453
Wavelength (nm)
Figure 3. Ultraviolet Spectrum of Sertraline HCl in Methanolic NaOH
Infrared Spectra The infrared spectra of sertraline hydrochloride (Form I) as a potassium bromide disc and as a Nujol mull were recorded on a Nicolet 5 10 FTIR spectrophotometer; the spectra in KBr and Nujol are virtually identical except for the Nujol-related bands. The spectra are presented in Figure 4. Assignments of absorption maxima are given below. 4.6.
Band (approx. cm-1)
Assignment
3100 - 3000 (w)*
Aromatic C-H stretching vibrations
3000 - 2800 (m)*
Aliphatic C-H stretching vibrations
27 10 - 2500 (m)
NH+ stretching vibration
2500 - 2450 (m)
NH+ stretching vibration
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
454
1585 (m) 1560 (m)
Aromatic C=C skeletal in-plane vibrations C-H stretching vibration; aromatic H
1470 - 1450 (s)*
Aliphatic C-H deformations, N-CH, stretching vibration
1400 (s), 1430 (m)
Asymmetric CH3 deformation
1375 (m)
Symmetric CH3 deformation
1340 (m) 1215 (m)
Aromatic C-H in-plane deformations
1135 (s)
Ahphatic secondary amine
1060 (m) 1030 (m) 1015 (m) 955 (m) 930 (m) 920 (m)
overtones and aromatic C-H in-plane deformations
825 (s) 800 (s) 790 (s) 760 (s) 710 (m) 700 (s) 670 (s)
aromatic C-H out-of-plane deformations; C-Cl stretching vibrations
* (w)=weak intensity; (m)=medium intensity; (s)=strong
intensity
The dlfferent polymorphs of sertraline hydrochloride yield different infrared spectra. Polymorphism is discussed more fully in section 4.13.
80 70 60
x
50
r a
40
T
n S
m
30
I
t t
20
a
n
C
10
a 0
-10
-20
-30 4000
U 2500
Figure 4. Infrared Spectra of Sertraline HCl in Nujol and KBr
m00
1500
1000
500
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BRUCE M. JOHNSON AND PEI-TEI L. CHANG
4.7.
Proton Nuclear Magnetic Resonance Spectra
The 300 MHz proton nuclear magnetic resonance spectrum of sertraline hydrochloride reference standard was recorded using a Briicker AM300 NMR instrument. The solvent was deuterated dimethylsulfoxide. Proton assignments are listed below, and the spectrum is reproduced as Figure 5. a
b
CI
Chemical Shift 1.9 - 2.4 ppm 2.6 ppm 4.1 - 4.2 ppm 4.4 - 4.5 ppm
6.7 - 6.8 ppm 7.2 - 7.4 ppm 7.35 - 7.5 ppm 7.5 - 7.65 ppm 7.7 ppm 7.75 - 8.0 ppm 9.5 - 9.8 ppm
Md tiDlicitv
# of Protons Assignment
broad, complex multiplet singlet broad, complex multiplet broad multiplet multiplet mu1tiplet multiplet doublet doublet multiplet broad singlet
4
d, e
3 1
a f
1 1 2 1 1 1 1 2
C
j k, 1 1
h g m b
451
SERTRALINE HYDROCHLORIDE
The peaks at 2.5 and 3.4 ppm are solvent related.
*
n
,a
.:.
.5
L.
u
,a
I .
u
*.
&,
<.
a.
u
u
u
.
.*
.r
,>
Figure 5. Proton NMR Spectrum of Sertraline HCl in DMSO-d6
4.8.
Carbon-13 Nuclear Magnetic Resonance Spectra
The carbon- 13 nuclear magnetic resonance spectrum of sertraline hydrochloride, Figure 6, was recorded using a Briicker WM250 instrument. The solvent was deuterated dimethylsulfoxide. Assignments have been allocated to the spectral lines where possible by reference to calculated shifts" and to information gained from low power noise and/or selective decoupling.
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BRUCE M. JOHNSON AND PEI-TEI L. CHANG
Cl
Chemical Shift.ppm 22.9 26.6 30.3 44.3 54.9 126.4 128.9 129.1 129.5 129.7 130.2 130.5 130.9 131.0 139.9 146.6
Assignment d C
a e b 0
i n
j P h,q (by intensity) g 1 f
The multiplet at 40 ppm is due to the solvent. Both the proton and carbon- 13 nuclear magnetic resonance spectra are consistent with the structure for sertraline hydrochloride.
I
180
170
160
I
150
'l
I
140
-
I-
130
' ~I
120
l
110
100
PPm
90
80
Figure 6. Carbon-13 NMR Spectrum of Sertraline HCl in DMSO
70
60
50
40
30
1
20
10
460
4.9.
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
Mass Spectra
The mass spectrum of sertraline hydrochloride was recorded using a Finnigan 45 10 mass spectrometer in the direct exposure electron impact mode. Instrument conditions are summarized below: Inlet system Accelerating voltage Electron ionization Ion source temperature Resolving power Calibration
Direct insertion probe 1.8 kV 70 eV 160°C lo00 perfluorotributylamine (FC-43) (nominal mass 614)
A representative spectrum is shown in Figure 7. Structure assignments for a number of the fragments are provided in Figure 8. These assignments were confmed by high resolution mass spectrometry, and the structures for the chlorine-containing fragments are consistent with the observed isotope ratios.I2 A typical spectrum (for peaks with relative intensity >6.0%) is summarized in the table below. The data are consistent with the structure for sertraline hydrochloride.
SERTRALINEHYDROCHLORIDE
46 1
Electron Impact Mass Spectrum of Sertraline Hydrochloride Mass vs Intensity (relative intensity >6.0%) Relative Intensity d Z 304 279 278 277 276 275 274 264 262 248 242 241 240 239 238 214 213 212 205 204 203 202 201 200 199 191 190 189 178 176 165 164 163 162 161 160
6.5 6.1 20.0 20.5 84.7 20.6 100.0 21.1 33.2 8.4 6.8 11.6 7.7 28.5 7.4 6.9 11.2 16.7 6.4 16.7 18.0 22.1 7.0 7.1 8.1 6.3 11.1 11.7 25.2 12.4 13.6 6.4 15.8 8.0 47.6 10.3
m/z
159 158 145 144 143 138.5 133 132 131 130 129 128 127 121.5 120.5 118 117 116 115 113 109 103 102 101 95 91 90 89 88 87 77 75 70 63 57 51
Relative Intensitv 99.4 10.4 19.6 18.8 7.6 8.9 44.7 44.2 11.7 22.4 33.2 30.6 14.3 13.0 24.8 18.4 14.7 35.3 36.4 7.9 12.3 67.6 31.5 20.3 14.4 23.8 6.2 15.2 8.8 8.8 9.4 8.3 15.8 7.5 6.3 6.4
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BRUCE M. JOHNSON AND PEI-TEI L. CHANG
Figure 7. Mass Spectrum of Sertraline HCl
SERTRALINE HYDROCHLORIDE
/It
463
+N
HN
’
I+ \
Vz c1
QC1
m/z 159
274
C1
Figure 8. Mass Spectrometric Fragmentation of Sertraline Hydrochloride
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BRUCE M. JOHNSON AND PEI-TEI L. CHANG
4.10. Optical Rotation Optical purity is determined by measuring the rotation of a 1% solution of sertraline hydrochloride in methanolic 0.05 N hydrochloric acid. The specific rotation found for the reference standard was 40.2".
4.11. pH and pKa The pKa of sertraline hydrochloride as determined by potentiometric titration in ethano1:water (1: 1, v/v) was found to be 8.5. The pKa determined in methano1:water (4060, v/v) was 8.6. Titration of sertraline hydrochloride in water was carried out in the presence of sodium chloride and a measured excess of HCl. Titration with NaOH provided a curve that was evaluated by the method of Clarke and C a h ~ n ' ~ The . pKa in water calculated by this method was 9.48 f 0.04.
4.12. Single Crystal X-Ray Perhaps the single best confirmatory evidence for the structure of the sertraline hydrochloride (Form I) molecule is provided by single crystal x-ray. A single crystal of sertraline hydrochloride was grown and its structure determined on a Nicolet R3M-m x-ray spectrometer. The resultant structure as determined is reproduced in Figure 9, which confirms the structure of sertraline hydrochloride.
SERTRALINE HYDROCHLORIDE
Single Crystal X-Ray Crystallographic Analysis of Sertraline Hydrochloride Crystal Parameters Crystal size, mm
0.11xo.11 x0.12
Cell Dimensions
a = 8.004(5) 8, b = 8.372(5) 8, c = 25.21(2) 8, a = 90.0" p = 90.0" x = 90.0" V = 1689.3(6) 8,3
Space group
~12121 Orthorhombic
Moleculedunit cell
4
Density observed, g/cm3
1.37
Density calculated, g/cm3
1.354
Linear absorption coefficient
49.48
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BRUCE M . JOHNSON AND PEI-TEI L. CHANG
466
CI
Figure 9. Single Crystal X-Ray Structure of Sertraline HCl (Form I)
SERTRALINE HYDROCHLORIDE
461
4.13. Polymorphism Five crystalline polymorphic forms of sertraline hydrochloride have been isolated and ~haracterized.'~ Four of the polymorphs have been examined by infrared absorption spectroscopy, X-ray powder diffraction, single crystal X-ray, differential scanning calorimetry (DSC), hot stage optical microscopy, and aqueous solubility studies. Only a few crystals of the fifth polymorph have been isolated and the only characterization data available are from single crystal X-ray studies and infrared spectra. The polymorphs of sertraline hydrochloride have been designated as Forms I, 11, 111, IV, and V. Form I represents the lower melting polymorph which may crystallize from an acidic solution of the compound in isopropyl alcohol, hexane, or ethyl acetate depending on temperature and rate of crystallization. Forms 11 and IV are metastable polymorphs which can be isolated by rapid crystallization of sertraline hydrochloride from various solvents (e.g., methanol, ethyl acetate, acetonitrile); however, slow crystallizations and granulations yield polymorph Form I. Form 111 is generated from Forms I, 11, or IV by heating the solid to temperatures above about 180°C. Granulating either Form 11, 111, or IV in isopropanol, ethyl acetate, or hexane at 40 to 60°C causes conversion to Form I. Form V is produced by sublimation of Form I onto a cold finger condenser. Form I is the thermodynamically most stable polymorph at room temperature. The following information summarizes observations concerning the characterization, stability, and thermal behavior of sertraline hydrochloride polymorphs. 4.13.1. Characterization Data Infrared Absorption Spectrophotometq The infrared absorption spectra of Forms I, 11, 111, IV,and V are different from one another (Figure 10). The spectra are obtained using KBr pellets to suspend the sample during
468
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
measurement. Figure 10 displays only the region of 1650 to 400 cm-1. The region from 4000 to 1650 cm-1 is not useful for comparing polymorphic differences. Qualitative comparison of the infrared spectra of Form I to Forms 11, 111, IV, and V show the following differences: a. At approximately 740 to 750 cm-l and 1075 to 1085 cm-1 Forms 11, 111, IV, and V exhibit absorption bands of significantly higher relative intensity. b. At approximately 780 cm-l Forms 11, 111, and IV exhibit major peaks. Forms I and V exhibit a major peak at approximately 790 cm-1with only a shoulder at about 780 cm-1. c. Forms 11, 111, IV, and V show absorption bands at approximately 870 and 520 to 540 cm-1 while no absorption is observed for Form I at these wavelengths. d. Form 11 shows a strong absorption band and Forms 111, IV, and V a weak band at about 640 cm-l, while a barely detectable absorption is observed for Form I.
e. Differences for Forms 11, 111, and IV are also observed in wavelength and relative intensity of the absorption bands in the region of 800 to 850 cm-1 compared to Forms I and V. Single Crystal X-Ray Analysis Absolute structure determination of Forms I, 11, HI, IV, and V by single crystai X-ray analysis shows that the polymorphic forms differ in rotational conformation at the methylamino and the dichlorophenyl positions. Forms 111and IV are similar rotationally but differ in their space group. Using these configurations the crystal packing diagrams are constructed and the crystal densities are calculated. Form I gives a density of 1.354 gkc, Form I1 gives a density of 1.314 g/cc, Form 111gives a density of 1.3 13 g/cc,
z T
I
a
n S
m I
t t
a n C 8
-120
4
Y 1600
1500
1400
1300
1200
1100
1mo
900
800
700
600
Figure 10. Infrared Spectra of Sertraline HCl Polymorphs (Wavelength range 1650 to 400 cm-1)
500
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BRUCE M. JOHNSON AND PEI-TEIL. CHANG
Form IV gives a density of 1.349 g/cc, and Form V gives a density of 1.308 g/cc. This result supports Form I as the thermodynamically stable form at room temperature since the most dense crystal at a given temperature is considered to be the most thermodynamically stabiei5. Using these single crystal data it is possible to calculate the theoretical powder diffraction patterns. The theoretical patterns shown in Figure 1 1 for Forms I, II, III, and IV match the observed patterns very closely. X-Ray Powder Diffraction The four polymorphs of sertraline hydrochloride for which samples are available give distinctive X-ray powder diffraction patterns. Each form has diffractions at unique values of 28 that are diagnostic: Form1
7.1, 12.7, 14.1, 15.3, 15.7,21.2,23.4, and26.3
Form11
5.4, 10.8, 14.6, 16.3, 18.1, 19.0,20.3,21.8, 24.4, and 27.3
FormIII
14.3, 15.5, 17.4, and 19.6
Form IV
15.6,22.4,25.4,28.9,31.9,and 32.1
In these powder diffraction patterns of the pure polymorphs, each of the unique peaks is greater than about 10%of the normalized intensity. In normal practice the 28 values remain constant but the relative intensities may vary somewhat due to particle size effects. Figure 1 1 shows the powder diffraction patterns calculated from the single crystal data. The pattern for Polymorph V is also included here and shows a distinctive pattern as well.
SERTRALINE HYDROCHLORIDE
47 1
POLYHORPH I
Figure 11. Calculated X-Ray Powder Diffraction Patterns 4.13.2. Relative Stability of Sertraline Hydrochloride Polymorphs Interconversion Experiments
Forms 11and TV have been made by rapid crystallization out of solvents and Form 111has been made by heating a sample of Form I at about 180°C for a period of several hours. When mixtures of Form I and Forms 11, 111, or IV were granulated in isopropyl alcohol at 50°C, the resulting solid was shown to be Form I. Similar behavior has been observed in other solvents. In an experiment viewed under the microscope at room temperature, a mixture of Forms I, 11, and 111was placed on a slide
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BRUCE M. JOHNSON AND PEI-TEI L. CHANG
and covered with a cover slip. Isopropanol saturated with sertraline hydrochloride was added at the edge of the cover slip and the sample was kept wet with solvent throughout the observation. Crystals of Form III disappeared fairly rapidly. Crystals of Form II shrunk in size slowly while the Form I crystals increased in size. In a similar experiment with Forms I and IV,Form IV dissolved slowly while Form I grew. These observations are consistent with the greater thermodynamic stability of Form I. Solubility The room temperature aqueous solubility of the four polymorphs is essentially equivalent at about 4 m u d . Polymorphs 11,III, and IV appear to be slightly more soluble than Form I, further indicating that Form I is the most stable at room temperature. 4.13.3. Thermal Behavior
Differential Scanning Calorimetry CDSC) The DSC thermograms for Forms I - IV are shown in Figures 12, 13, 14, and 15. The features in the thermograms may be interpreted as follows:
Form I shows an endotherm with an onset temperature of about 219°C resulting from the melting of Form I. An exotherm immediately following the melting endotherm of Form I appears at about 225°C caused by partial crystallization of the melt to Form III, and a second endotherm appears with an onset at about 246°C resulting from the melting of Form III. Rapid thermal decomposition takes over after the final melt of Form III causing the baseline to increase rapidly and become erratic in appearance. On rare occasions, the DSC of Form I shows only a single melting endotherm with an onset temperature of about 219°C. This can occur when the sample does not have sufficient time or seed to
SERTRALINE HYDROCHLORIDE
413
recrystallize as Form 111prior to reaching the Form 111melting temperature.
In the thermograms obtained for Forms 11and IV,a very small endotherm may be observed with an onset temperature at about 180°C which corresponds to a solid-solid transition to Form 111. This event is followed by melting of Form 111at about 246°C. The thermogram obtained for Form 111 shows a single endotherm at about 246°C. Above the melting temperature of 246" C thermal decomposition increases rapidly. The thermal events discussed above demonstrate that Form 111undergoes only a single melting process at 246°C followed by increased thermal decomposition after the melt has occurred. Thermogravimetry and hot stage optical microscopy reveal that all four forms undergo slight decomposition and sublimation at temperatures above about 160°C. Prolonged heating studies on the Form Worm 111 conversion in the solid state have shown that below 160°C Form I is the preferred polymorph. Above 180°C Form I converts to Form 111in the solid state. This conversion takes place at varying rates in the DSC experiment depending on sample characteristics such as particle size, previous handling, or the presence of Form III seed. Thus, in some instances the first endotherm in Form I may show a smaller endotherm with a lower onset temperature as a result of solid state conversion of Form I to Form 111during heating. The solid state conversion is a very low energy transition and fails to give a reliably detectable DSC event. A sample of Form I spiked with 3% of Form 111(Figure 16) shows an endotherm for the solid state transition and the absence of the Form I melting endotherm. The Form 111endotherm appears at the expected temperature of about 246°C. Under the conditions of this DSC experiment the solid state transition is fast enough to cause complete conversion to Form 111before the Form I melt temperature is reached. Similar
BRUCE M.JOHNSON AND PEI-TEI L.CHANG
474 01
Figure 12. DSC Thermogram of Sertraline HCl Form I)
u
I V
c
m
aa
Figure 13. DSC Thermogram of Sertraline HCl (Form II)
SERTRALINE HYDROCHLORIDE
415
I
Figure 14. DSC Thermogram of Sertraline HCl (Form III)
Figure 15. DSC Thennogram of Sertraline HCl (Form IV)
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
476 LOO
U
s
LSD
-I
0.w
Figure 16. DSC Thermogram of Sertraline HCl (Form I containing 3% of Form 111) behavior was observed in two other samples of Form I spiked with 5% of Form I1 or 5% of Form IV.
In a related experiment, small amounts of each of Forms I, 11, and IV were heated to 185°C for 15 minutes. The infrared spectra of each sample confmed that they had converted to Form 111. Hot Stage Optical Microscopy Microscopic observation of a Form I sample heated on a hol stage is consistent with the observed DSC behavior. At about 150 to 180°C the sample begins to move about and appears to "pop". This may be caused by the onset of decomposition, solvent release, or sublimation. Partial melting may be observed at about 210 to 220°C with the formation of some new crystals (Form 111) as the temperature is raised to about 235°C. (In some instances, a solidsolid transition to Form I11 is observed at temperatures above about
SERTRALINE HYDROCHLORIDE
411
180°C.) At about 245 to 250°C the newly formed crystals melt completely. The melt solidifies very slowly upon cooling and usually remains as a yellowish glass. This suggests that significant decomposition has taken place. In mixtures of Form I11 in Form I, the first melt at 210 to 220°C does not cause all of the sample to liquefy, a small number of crystals may remain and increase in size as Form 111crystallizes around them. Holding the temperature at about 235°C permits the melt to recrystallize to Form III. Cooling this melt to room temperature and subsequent reheating does not show the Form I melt at 210 to 220°C. This suggests that the conversion to Form 111is not rapidly reversible under these conditions. Microscopic observation of Forms 11or IV on the hot stage shows an apparent solidkolid transition at about 180°C without evidence of melting. Continued heating gives a complete melt at about 245°C. The temperature region of 180 to 230°C appears also to cause decomposition and sublimation. Microscopic observation of Form 111 shows sample movement similar to Form I at about 160°C followed by melting at about 245 to 250°C. No other thermal events are seen and the observation is consistent with the DSC behavior. When samples are heated in silicone oil the appearance of gas bubbles is observed starting at around 150 to 180°C suggesting the onset of decomposition. The yellowish color of the melt above 250°C results from chemical decomposition of the sample. This phenomenon occurs for all four polymorphic forms.
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
47%
4.13.4. Literature Precedent Polymorphs of sertraline hydrochloride behave similarly to those of gepirone hydrochloride which has been characterized and discussed in the 1iteraturel6. Both compounds have a polymorph which is most thermodynamically stable at room temperature which can go through an endothermic melt and subsequently recrystallize as a higher melting polymorph.
5.
Methods of Analysis 5.1.
Elemental Analysis
The elemental composition of sertraline hydrochloride was determined by a series of microanalytical determinations. A typical set of analyses is shown below. Assay % carbon % hydrogen % nitrogen % chlorine, ionic % chlorine, total
Total (C,H,N,Cl)
59.54 5.30 3.85 10.24 30.54 99.23
59.58 5.29 4.09 10.35 31.04 100.00
The results for percentage carbon, hydrogen, nitrogen, and chlorine for sertraline hydrochloride are consistent with the theoretical values for the formula C17HIgNC13. 5.2.
Ionic Chlorine
The ionic chlorine content of sertraline hydrochloride may be determined by potentiometric titration with a standard silver nitrate solution, which precipitates the chloride ion as AgC1. Titration is carried out by dissolving the sertraline hydrochloride in ethanovwater (1: 1, v/v) and titrating using a silver measuring electrode and a Ag/ AgCl reference electrode. The theoretical ionic
SERTRALINE HYDROCHLORIDE
479
chloride content of sertraline hydrochloride is 10.35%;the amount found for the reference standard lot was 10.24%.
5.3.
Identification
Sertraline hydrochloride is identified in the bulk form using the infrared spectrum, the TLC retention, and the HPLC retention by comparison with a working standard. In dosage forms the TLC retention and the HPLC retention are used for confirming identity of drug substance.
5.4.
Thin Layer Chromatography
Thin layer chromatography is used as a technique for establishing the identity of sertraline and for examining for the presence of process related substances and other potential impurities. The following systems have been used with silica gel 60 F-254 (Merck Darmstadt) plates. Solvent System
Rf
Detection
Ethyl acetate/Methanol/Ammonium acetate 160:40:2 v/v
0.55
1
Chloroform
0.00
2
Chloroform/Methanol/ammoniumacetate 12050:15 v/v
0.91
2
Detection Systems 1 2
5.5.
Dragendorff's Reagent Ultraviolet light - 254 nm
Ultraviolet Spectroscopy
Assay for sertraline content of drug substance and drug products may be carried out using ultraviolet spectrophotometry.
BRtiCE M. JOHNSON AND PEI-TEI L. CHANG
480
Sertraline solutions are prepared in 0.01 N methanolic hydrochloric acid at a concentration of approximately 0.05 mg/mL. Absorbance measurements are taken at 273 nm and compared to the absorbance of a well characterized standard.
5.6.
Potentiometric Titration
Being a hydrochloride salt, sertraline hydrochloride has an acidic proton which can be titrated with 0.5 N aqueous sodium hydroxide in the solvent mixture ethanovwater, 1:1, v/v. When 98.67 mg of sertraline hydrochloride reference standard was titrated in 20 mL of the solvent mixture, a single inflection point was observed. This was attributed to the single acidic proton located on the arnine nitrogen of the sertraline hydrochloride molecule. The neutralization equivalent (molecular weight) calculated for the single inflection point was 345.5. Based on this result, an assay of 89.3% sertraline was calculated for the reference standard lot, which is 99.9% of theory (89.4%). This titrimetric result confirms the stoichiometry of sertraline hydrochloride and provides an equivalent weight value consistent with the structure. A representative curve for this titrimetric procedure is included in Figure 17.
5.7.
High Performance Liquid Chromatography
Purity assay of sertraline hydrochloride is done using HPLC by the external standard method by comparing chromatographic response with a well characterized standard. An isocratic reverse phase system using a C-18 column and UV detection at 254 nm is suitable for both drug substance and formulated products. Column: Detector: Mobile Phase: Buffer:
Waters Nova-Pak C- 18 UV at 254 nm
Acetonitrile/MethanoYSuffer 45: 15:40 v/v 0.05 M Acetic acid/O.OZ M Triethylamine (aqueous)
SERTRALINE HYDROCHLORIDE
481
PH
0 -
9 1 2 3 4 6 6 7 8 P 1 9 1 1 1 2 1 1 1 4 1 1 1 1 l l 1 1 1 1 l l l l 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
0.10
0.20
0.30
-
-
0.40 mL
-
0.60
-
0.60
-
0.70
-
0.80
-
Figure 17. Potentiometric Titration of Sertraline HCl in EthanoVWater (1:l)
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
4x2
Metabolic studies have used HPLC to measure sertraline and its metabolites in urine, bile, and feces using radiolabeled drug17 and a radioactivity detector and/or a variable wavelength UV detector’*. Two different mobile phases were reported. Column: Waters C - 18 pBondapak Berthold radioactivity monitor or UV Detector: Mobile Phase 1 : Acetonitrile/SO mM Sodium phosphate (pH 4.5) 5050 v/v Mobile Phase 2: AcetoniUilelSO mM Ammonium acetate (pH 5.0) 33167v/v
Another HPLC method has been reported for measuring sertralirie and desmethylsertraline in mouse cerebral cortex using an internal standard method”.
Column: Detector: Mobile Phase:
5.8.
Versapack C- 18 UV at 235 nm Acetonitrile/0.25 M Potassium phosphate (pH 2.7) 30:70 v/v
Gas Liquid Chromatography
Gas liquid chromatography is used to separate sertraline from its process related substances, in particular the dechlorinated homologs. Hydrochloride salts are converted to their free base form by extraction of a basified solution into methylene chloride prior to injection. The following system has been used for the drug substance. Column:
Column Temp: Injector Temp: Detector Temp: Detector:
5% OV-17 on Chromosorb W (acid washed and DMCS treated) packed in a 7 ft. x 0.25 in. OD glass column 225°C 250°C 300°C Flame ionization
SERTRALINE HYDROCHLORIDE
483
Gas chromatography has also been used to measure sertraline levels in biological fluids. The drug is extracted from plasma and derivatized with trifluoroacetic anhydride. The derivative is chromatographed using either a mass spectrometric detector2' or a 63Ni electron capture detector21. GCMS Method Column: 3% Silar 1OC on Gas Chrom Q (80 - 100 mesh) packed in a 0.8 m x 2 mm ID glass column Column Temp: 255°C Injector Temp: 200°C Transfer Temp: 290°C Detector: Mass spectrometer Electron Capture Method Column: SE-54,0.25 pm film thickness, 12 m x 0.32 mm ID capillary column Column Temp: 165°C for 0.5 min, 20"C/min to 21OoC, hold for 12 min Injector Temp: 260°C Detector Temp: 300°C Detector: 63Ni Electron Capture
5.9.
Biological Fluids
The levels of sertraline and its major metabolites are measured in biological fluids by HPLC, GC/EC, and GCMS using the methods described above. Metabolism studies have resulted in the identification of N-desmethylsertraline, sertraline carbamoyl-0glucuronide, N-hydroxysertraline, a ketone [4-S-(3,4dichlorophenyl)-3,4-dihydro-1(2H)-naphthalenone], and the ahydroxyketone [4-S-(3,4-dichlorophenyl)-3,4-dihydro-2-R,Shydroxy-1(2H)-naphthalenone] as well as the glucuronides of Nhydroxysertraline and the a-hydroxyketone2*.
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
484
6.
Stability The stability of sertraline hydrochloride has been studied under extreme challenge conditions as well as the more traditional pharmaceutical challenge conditions. The extreme conditions included exposing excess drug substance to refluxing water for 3 hours, refluxing 5 N hydrochloric acid for 3 hours, refluxing 5 N NaOH for 3 hours, or 10% hydrogen peroxide for 6 hours. The more traditional stability challenge conditions of 3 months at 50°C, 12 months at 37"C, 60 months at 30°C, or 3 months in a light cabinet were used with different packaging systems. Careful examination of the resulting samples revealed no significant degradation under any of the conditions used in these studies. The only trace degradation product identified was the ketone [4-S-(3,4dichlorophenyl)-3,4-dihydro-1(2H)-naphthalenone] which has also been identified as a metabolite. Sertraline hydrochloride appears to be a very stable compound under a variety of challenge conditions.
7.
Pharmacokinetics and Metabolism 7.1.
Systemic Bioavailability
In man, following oral once-daily dosing of sertraline hydrochloride (Form I) over the range of 50 to 200 mg for 14 days, mean peak plasma concentrations (C,) of sertraline occurred between 4.5 to 8.4hours postdosing. The average terminal elimination half-life of plasma sertraline is about 26 hours. Based on this pharmacokinetic parameter, steady-state sertraline plasma levels should be achieved after approximately one week of oncedaily dosing. Linear dose-proportional pharmacokinetics were demonstrated in a single dose study in which the C, and area under the plasma concentration time curve (AUC) of sertraline were proportional to dose over a range of 50 to 200 mg. Consistent with the terminal elimination half-life, there is an approximately two-fold accumulation, compared to a single dose, of sertraline with repeated dosing over a 50 to 200 mg dose range. The single dose bioavailability of sertraline tablets is approximately equal to an equivalent dose of solution23.
SERTRALINE HYDROCHLORIDE
485
The effects of food on the bioavailability of sertraline were studied in subjects administered a single dose with and without food. AUC was slightly increased when drug was administered with food but the C, was 25% greater, while the time to reach peak plasma concentration decreased from 8 hours post-dosing to 5.5 hours. 7.2.
Metabolism
Sertraline undergoes extensive first pass metabolism. The principal initial pathway of metabolism for sertraline is Ndemethylation. N-desmethylsertraline has a plasma terminal elimination half-life of 62 to 104 hours. Both in vitro biochemical and in viva pharmacological testing have shown Ndesmethylsertraline to be substantially less active than sertraline. Both sertraline and N-desmethylsertraline undergo oxidative deamination and subsequent reduction, hydroxylation, and glucuronide conjugation. In a study of radiolabeled sertraline involving two healthy male subjects, sertraline accounted for less than 5% of the plasma radioactivity. About 40-45% of the administered radioactivity was recovered in urine in 9 days. unchanged sertraline was not detectable in the urine. For the same period, about 40-45% of the administered radioactivity was accounted for in feces, including 12-14%unchanged sertralineZ4. Desmethylsertraline exhibits time-related, dose dependent and Cmin, with about a 5-9 increases in AUC (0-24 hour), C, fold increase in these pharmacokinetic parameters between day 1 andday 14.
Acknowlegement The authors wish to thank our many Pfizer colleagues in the Central Research laboratories in both Groton, CT, USA and Sandwich, Kent, UK who have contributed to the development of sertraline hydrochloride and to the information presented in this overview.
486
References
BRUCE M.JOHNSON AND PEI-TEI L. CHANG
'Koe, B. K.; Weissman, A.; Welch, W. M.; Browne, R. G. J. Exp. Ther. 1983,226, 686. 2Package Insert, Zoloft*, Pfizer Inc, Jan. 1992 3Quallich, G. J.; Williams, M. T. U.S. Patent 4 777 288, 1988. 'Quallich, G. J.; Williams, M. T. U.S. Patent 4 839 104, 1989. 5Williams, M. T.; Quallich, G. J. Chemistry and Industry 1990,21, 315. 6Adrian, G. P. U.S. Patent 5 019 655,1991. 'Quallich, G. J.; Williams, M. T. European Patent 0 295 050 A l , 1988. 'Quallich, G . J.; Williams, M. T.; Friedmann, R. C. J. Org. Chem. 1990,55,4971. w e l c h , W. M.; Kraska, A. R.; Sarges, R.; Koe,B. K. J. Med. Chem. 1984,27, 1508. '()Welch, Jr., W. M.; Harbert, C. A.; Koe, B. K.; Kraska, A. R. U.S. Patent 4 536 518, 1985. "Ewing, D. F. Organic Magnetic Resonance 1979, 12(9), 499. 12 Sharp, T. R.; Horan, G. J.; Day, S.V.O. Proceedings of the 41st ASMS Conference 01 Mass Spectrometry and Allied Topics, San Francisco, California, 1993. I3Clarke, F. H.; Cahoon, N. M. J. Pharm. Sci. 1987,8,611. '*Sysko, R. J.; Allen, D. M. J. US.Patent 5 248 699, 1993. "Haleblian, J.; McCrone, W. J. Pharm. Sci. 1969,58(8), 911. %ehme, R. J.; Brooke, D.; Farney, R. F.; Kensler, T. T. J. Pharm. Sci. 1985, 74(10), 1041. "Welch, W. M.; Vivieros, D. M. J. Labelled Compd. Radiopkam. 1987, 24, 987. 18 Tremaine, L. M.; Stroh, J. G.; Ronfeld, R. A. Drug Metab. Dispos. 1989, 17,58. 'weiner, H. L.; Kramer, H. K.; Reith, M. E. A. J. Chromatog. 1990,527,467. 2%ouda, H. 6.; Ronfeld, R. A.; Weidler, D. J. J. Chromatog. 1987,417, 197. "Tremaine, L. M.; Joerg, E. A. J. Chromatog. 1989,496,423. 2?remaine, L. M.; Welch, W. M.; Ronfeld, R. A. Drug Metab. Dispos. 1989, 17, 542. 23PackageInsert, Zolofi@,Pfizer Inc, Jan. 1992 24 Package Insert, Zoloft@, Pfizer Inc, Jan. 1992
Bruce M. Johnson and Pei-Tei L. Chang
Central Research Pfizer Inc Groton, CT 06340
ANALYTICAL PROFILES OF DRUG SUBSTANCES AND EXCIPIENTS-VOLUME 24
443
Copyright 0 1996 by Academic Press, Inc. All rights of reproductionin any form reserved.
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BRUCE M. JOHNSON AND PEI-TEI L. CHANG
SERTRALXNE HYDROCHLORIDE 1. Introduction 2. Description 2.1. Structural Formula 2.2. Molecular Formula and Molecular Weight 2.3. Nomenclature 2.4. Laboratory Codes 3. Synthesis 4. Physico-Chemical Properties 4.1. Appearance, Color, Odor 4.2. Melting range 4.3. Solubility 4.4. Hygroscopicity 4.5. Ultraviolet Spectra 4.6. Infrared Spectra 4.7. Proton Nuclear Magnetic Resonance Spectra 4.8. Carbon- 13 Nuclear Magnetic Resonance Spectra 4.9. Mass Spectra 4.10. Optical Rotation 4.11. pH andpKa 4.12. Single Crystal X-Ray 4.1 3. Polymorphism 5. Methods of Analysis 5.1. Elemental Analysis 5.2, Ionic Chlorine 5.3. Identification 5.4. Thin Layer Chromatography 5.5, Ultraviolet Spectroscopy 5.6. Potentiometric Titration 5.7. High Performance Liquid Chromatography 5.8. Gas Liquid Chromatography 5.9. Biological Fluids 6 . Stability 7. Pharmacokinetics and Metabolism 7.1. Systemic Bioavailability 7.2. Metabolism
SERTRALINE HYDROCHLORIDE
1.
445
introduction Sertraline hydrochloride is an antidepressant for oral administration. It is chemically unrelated to tricyclic, tetracyclic, or other available antidepressant agents. It is a novel inhibitor of serotonin reuptake in the brain'. The mechanism of action of sertraline is presumed to be linked to its inhibition of CNS neuronal uptake of serotonin (5HT).Studies at clinically relevant doses in man have demonstrated that sertraline blocks the uptake of serotonin into human platelets. Studies in animals also suggest that sertraline is a potent and selective inhibitor of neuronal serotonin reuptake and has only very weak effects on norepinephrine and dopamine neuronal reuptake. In vifrostudies have shown that sertraline has no significant affinity for adrenergic (alpha 1, alpha 2, beta), cholinergic, GABA, dopaminergic, histaminergic, and serotonergic (5HT1A, SHTlB, 5HT2)or benzodiazepine receptors; antagonism of such receptors has been hypothesized to be associated with various anticholinergic, sedative, and cardiovascular effects for other psychotropic drugs. The chronic administration of sertraline was found in animals to downregulate brain norepinephrine receptors, as has been observed with other clinically effective antidepressants. Sertraline does not inhibit monoamine oxidase.*
2.
Description
2.1.
Structural Formula
Sertraline is the S-cis enantiomer of a disubstituted tetrahydronaphthalene. The structural formula of sertraline hydrochloride is given below:
446
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
H-N-CH,
I
mHCI
Cl
Sertraline Hydrochloride 2.2.
2.3.
Molecular Formula and Molecular Weight Molecular Formula
Sertraline
c1 7H 17Nc12
Molecular Weight 306.2
Sertraline hydrochloride
Cl7H@C13
342.7
Nomenclature
Chemical Names: 1. ( 1S-cis)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-Nmethyl-1-naphthalenaminehydrochloride (CAS-79559-97-0) Preferred use name.
2. cis-( lS,4S)-N-rnethyl-4-(3,4-dichlorophenyl)-1,2,3,4tetrahydro- 1-naphthalenamine hydrochloride (J. Med. Chern. 1984, 27(11), 1508) 3. cis-( 1S)-N-methyl-4-(3,4-dichlorophenyl)-1,2,3,4tetrahydro- 1-naphthalenamine hydrochloride (US Patent 4,536318)
SERTRALINE HYDROCHLORIDE
441
4. 1-naphthalenamine,4-(3,4-dichlorophenyl)-1,2,3,4tetrahydro-N-methyl, hydrochloride, ( 1S-cis)- (USAN chemical name 1) 5. (lS,4S)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydro-Nmethyl- 1-naphthylamine hydrochloride (USAN chemical name 2)
2.4.
B.A.N.:
Sertraline hydrochloride
U.S. A.N. :
Sertraline hydrochloride
I.N.N.:
Sertraline hydrochloride
Proprietary or Trade Name:
Zolofim (USA) LustralTM(UK)
Laboratory Codes Sertraline has the Pfizer code CP-5 1,974 Sertraline hydrochloride has the Pfizer code CP-5 1,974-01
Synthesis The pure drug substance is manufactured from commonly available intermediates using a four step process. The structurally significant starting material is 4-(3,4-dichlorophenyl)-3,4-dihydro-1(2H)n a p h t h a l e n ~ n e which ~ s ~ ~is~reacted ~ ~ ~ ~with ~ methylamine to form the imine. The imine, (N-[4-(3,4-dichlorophenyl)-3,4-dihydro1(2H)-naphthalenylidenelmethanamine), is reduced by catalytic hydrogenation to a pair of racemic diastereomers. The racemic cis isomers are separated from the racemic trans isomers by selective crystallization of the hydrochloride salts. The racemic cis enantiomers are then resolved with D(-)-mandelic acid. In the final step the mandelate counterion is replaced by chloride to give the finished drug substance, sertraline hydrochloride.’* lo Crystallization conditions in the final step determine the polymorphic form produced.
BRUCE M.JOHNSON AND PEI-TEI L. CHANG
448
4.
Physico-Chemical Properties
4.1.
Appearance, Color, Odor
Sertraline hydrochloride is a white to off-white, crystalline powder having no odor. It is an irritant, contact with skin and eyes should be avoided.
4.2.
Melting range
Determination of the melting point by the capillary method in a Buchi 510 melting point apparatus with a heating rate of 1°C per minute on Form I shows the onset of change at about 160 to 180°C with movement of the sample and a slight color change. At about 218°C a partial melt is observed but the sample does not become clear until a temperature of 245 to 250°C is reached. This is consistent with the DSC and hot stage microscopic observations.
4.3.
Solubility
4.3.1. Aqueous Solubility The solubility of a saturated solution of sertraline hydrochloride (Form I) in distilled water at room temperature is 3.8 mg/mL. The pH of this saturated solution is 5.3. Solubility in water is pH dependent, as the data in the following table shows. These data were determined by preparing a saturated solution in distilled water, with pH adjustments made by addition of sodium hydroxide and/or hydrochloric acid, followed by appropriate filtering, diluting, and assay by HPLC.
SERTRALINE HYDROCHLORIDE
DH
1 .o 2.0 2.9 4.2 6.0 6.2 6.3 6.5 7.2 7.7 8.8 9.8 10.2 11.1 12.1
449
Solubility (mg/mL) 0.89 2.98 3.88 4.07 4.46 4.93 4.93 3.32 0.72 0.21 0.02 0.006
0.004
0.004 CO.004
4.3.2. Solubility in Other Solvents The approximate solubility of sertraline hydrochloride in selected solvents at room temperature is given below. These data were obtained at room temperature, with saturated solutions that were appropriately filtered, diluted, and assayed by HPLC. Solvent Aqueous 0.1 N HC1 Aqueous 0.1 N NaOH Ethanol Isopropyl alcohol Chloroform Acetone N,N-dimethy1formamide Dimethylsulfoxide Ethyl acetate Acetonitrile Methanolic 0.1 N HC1 Chloroform/methanol, 1: 1
Solubility (mg/mL,) 0.5 1 0.002 15.7 4.3 110 1.1 88 147 0.20 0.85 47 134
450
4.4.
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
Hygroscopicity
The hygroscopicity of sertraline hydrochloride (Form I) was determined by exposing a sample for one week to an atmosphere of 37"C/75% relative humidity, and a sample to room temperature/88% relative humidity. Karl Fischer titration was used to determine water content. The results showed water contents of
4.5.
Ultraviolet Spectra
The ultraviolet absorption spectra of sertraline hydrochloride were recorded in methanol, methanolic 0.01 N hydrochloric acid, and methanolic 0.01 N sodium hydroxide. These spectra are presented as Figures 1,2, and 3. below:
Absorptivity data for sertraline hydrochloride are given
265 273 28 1
Absorptivity 2.58 3.04 1.64
Methanol
265 273 28 1
2.61 3.06 1.64
0.01 N NaOWMethanol
265 273 28 1
1.92 2.26 1.60
Solvent 0.01 N HCYMethanol
&-nm
SERTRALINE HYDROCHLORIDE
45 1
The table below demonstrates that the absorptivity and hremain effectively unchanged in solutions of differing acid strengths. Acid Strength 0.005 N 0.01 N 0.05 N 0.10 N 0.50 N
Lax
273 273 273 273 273
Absorptivity 3.03 3.04 3.1 1 3.03 3.04
Sertraline hydrochloride also adheres to Beer's Law at this wavelength, as evidenced by the following data: Concentration (mg/mL) 0.101 0.201 0.302 0.402 0.503 0.603 0.704 0.804 0.905 1.01 avg. k std. dev.
Lax 273 273 273 273 273 273 273 273 273 273
Absorptivity 2.99 2.97 3.04 2.99 2.99 3.01 2.96 2.97 2.95 2.88 2.98 f 0.04
BRUCE M.JOHNSON AND PEI-TEI L.CHANG
452
A b S
0
r
b a
n C
e
Figure 1. Ultraviolet Spectrum of Sertraline HC1 in Methanol
i
2.0
A b S 0
r
b a
n C
Wawkngth (nm)
Figure 2. Ultraviolet Spectrum of Sertraline HCl in Methanolic HCl
SERTRALINEHYDROCHLORIDE
453
Wavelength (nm)
Figure 3. Ultraviolet Spectrum of Sertraline HCl in Methanolic NaOH
Infrared Spectra The infrared spectra of sertraline hydrochloride (Form I) as a potassium bromide disc and as a Nujol mull were recorded on a Nicolet 5 10 FTIR spectrophotometer; the spectra in KBr and Nujol are virtually identical except for the Nujol-related bands. The spectra are presented in Figure 4. Assignments of absorption maxima are given below. 4.6.
Band (approx. cm-1)
Assignment
3100 - 3000 (w)*
Aromatic C-H stretching vibrations
3000 - 2800 (m)*
Aliphatic C-H stretching vibrations
27 10 - 2500 (m)
NH+ stretching vibration
2500 - 2450 (m)
NH+ stretching vibration
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
454
1585 (m) 1560 (m)
Aromatic C=C skeletal in-plane vibrations C-H stretching vibration; aromatic H
1470 - 1450 (s)*
Aliphatic C-H deformations, N-CH, stretching vibration
1400 (s), 1430 (m)
Asymmetric CH3 deformation
1375 (m)
Symmetric CH3 deformation
1340 (m) 1215 (m)
Aromatic C-H in-plane deformations
1135 (s)
Ahphatic secondary amine
1060 (m) 1030 (m) 1015 (m) 955 (m) 930 (m) 920 (m)
overtones and aromatic C-H in-plane deformations
825 (s) 800 (s) 790 (s) 760 (s) 710 (m) 700 (s) 670 (s)
aromatic C-H out-of-plane deformations; C-Cl stretching vibrations
* (w)=weak intensity; (m)=medium intensity; (s)=strong
intensity
The dlfferent polymorphs of sertraline hydrochloride yield different infrared spectra. Polymorphism is discussed more fully in section 4.13.
80 70 60
x
50
r a
40
T
n S
m
30
I
t t
20
a
n
C
10
a 0
-10
-20
-30 4000
U 2500
Figure 4. Infrared Spectra of Sertraline HCl in Nujol and KBr
m00
1500
1000
500
456
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
4.7.
Proton Nuclear Magnetic Resonance Spectra
The 300 MHz proton nuclear magnetic resonance spectrum of sertraline hydrochloride reference standard was recorded using a Briicker AM300 NMR instrument. The solvent was deuterated dimethylsulfoxide. Proton assignments are listed below, and the spectrum is reproduced as Figure 5. a
b
CI
Chemical Shift 1.9 - 2.4 ppm 2.6 ppm 4.1 - 4.2 ppm 4.4 - 4.5 ppm
6.7 - 6.8 ppm 7.2 - 7.4 ppm 7.35 - 7.5 ppm 7.5 - 7.65 ppm 7.7 ppm 7.75 - 8.0 ppm 9.5 - 9.8 ppm
Md tiDlicitv
# of Protons Assignment
broad, complex multiplet singlet broad, complex multiplet broad multiplet multiplet mu1tiplet multiplet doublet doublet multiplet broad singlet
4
d, e
3 1
a f
1 1 2 1 1 1 1 2
C
j k, 1 1
h g m b
451
SERTRALINE HYDROCHLORIDE
The peaks at 2.5 and 3.4 ppm are solvent related.
*
n
,a
.:.
.5
L.
u
,a
I .
u
*.
&,
<.
a.
u
u
u
.
.*
.r
,>
Figure 5. Proton NMR Spectrum of Sertraline HCl in DMSO-d6
4.8.
Carbon-13 Nuclear Magnetic Resonance Spectra
The carbon- 13 nuclear magnetic resonance spectrum of sertraline hydrochloride, Figure 6, was recorded using a Briicker WM250 instrument. The solvent was deuterated dimethylsulfoxide. Assignments have been allocated to the spectral lines where possible by reference to calculated shifts" and to information gained from low power noise and/or selective decoupling.
458
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
Cl
Chemical Shift.ppm 22.9 26.6 30.3 44.3 54.9 126.4 128.9 129.1 129.5 129.7 130.2 130.5 130.9 131.0 139.9 146.6
Assignment d C
a e b 0
i n
j P h,q (by intensity) g 1 f
The multiplet at 40 ppm is due to the solvent. Both the proton and carbon- 13 nuclear magnetic resonance spectra are consistent with the structure for sertraline hydrochloride.
I
180
170
160
I
150
'l
I
140
-
I-
130
' ~I
120
l
110
100
PPm
90
80
Figure 6. Carbon-13 NMR Spectrum of Sertraline HCl in DMSO
70
60
50
40
30
1
20
10
460
4.9.
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
Mass Spectra
The mass spectrum of sertraline hydrochloride was recorded using a Finnigan 45 10 mass spectrometer in the direct exposure electron impact mode. Instrument conditions are summarized below: Inlet system Accelerating voltage Electron ionization Ion source temperature Resolving power Calibration
Direct insertion probe 1.8 kV 70 eV 160°C lo00 perfluorotributylamine (FC-43) (nominal mass 614)
A representative spectrum is shown in Figure 7. Structure assignments for a number of the fragments are provided in Figure 8. These assignments were confmed by high resolution mass spectrometry, and the structures for the chlorine-containing fragments are consistent with the observed isotope ratios.I2 A typical spectrum (for peaks with relative intensity >6.0%) is summarized in the table below. The data are consistent with the structure for sertraline hydrochloride.
SERTRALINEHYDROCHLORIDE
46 1
Electron Impact Mass Spectrum of Sertraline Hydrochloride Mass vs Intensity (relative intensity >6.0%) Relative Intensity d Z 304 279 278 277 276 275 274 264 262 248 242 241 240 239 238 214 213 212 205 204 203 202 201 200 199 191 190 189 178 176 165 164 163 162 161 160
6.5 6.1 20.0 20.5 84.7 20.6 100.0 21.1 33.2 8.4 6.8 11.6 7.7 28.5 7.4 6.9 11.2 16.7 6.4 16.7 18.0 22.1 7.0 7.1 8.1 6.3 11.1 11.7 25.2 12.4 13.6 6.4 15.8 8.0 47.6 10.3
m/z
159 158 145 144 143 138.5 133 132 131 130 129 128 127 121.5 120.5 118 117 116 115 113 109 103 102 101 95 91 90 89 88 87 77 75 70 63 57 51
Relative Intensitv 99.4 10.4 19.6 18.8 7.6 8.9 44.7 44.2 11.7 22.4 33.2 30.6 14.3 13.0 24.8 18.4 14.7 35.3 36.4 7.9 12.3 67.6 31.5 20.3 14.4 23.8 6.2 15.2 8.8 8.8 9.4 8.3 15.8 7.5 6.3 6.4
462
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
Figure 7. Mass Spectrum of Sertraline HCl
SERTRALINE HYDROCHLORIDE
/It
463
+N
HN
’
I+ \
Vz c1
QC1
m/z 159
274
C1
Figure 8. Mass Spectrometric Fragmentation of Sertraline Hydrochloride
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BRUCE M. JOHNSON AND PEI-TEI L. CHANG
4.10. Optical Rotation Optical purity is determined by measuring the rotation of a 1% solution of sertraline hydrochloride in methanolic 0.05 N hydrochloric acid. The specific rotation found for the reference standard was 40.2".
4.11. pH and pKa The pKa of sertraline hydrochloride as determined by potentiometric titration in ethano1:water (1: 1, v/v) was found to be 8.5. The pKa determined in methano1:water (4060, v/v) was 8.6. Titration of sertraline hydrochloride in water was carried out in the presence of sodium chloride and a measured excess of HCl. Titration with NaOH provided a curve that was evaluated by the method of Clarke and C a h ~ n ' ~ The . pKa in water calculated by this method was 9.48 f 0.04.
4.12. Single Crystal X-Ray Perhaps the single best confirmatory evidence for the structure of the sertraline hydrochloride (Form I) molecule is provided by single crystal x-ray. A single crystal of sertraline hydrochloride was grown and its structure determined on a Nicolet R3M-m x-ray spectrometer. The resultant structure as determined is reproduced in Figure 9, which confirms the structure of sertraline hydrochloride.
SERTRALINE HYDROCHLORIDE
Single Crystal X-Ray Crystallographic Analysis of Sertraline Hydrochloride Crystal Parameters Crystal size, mm
0.11xo.11 x0.12
Cell Dimensions
a = 8.004(5) 8, b = 8.372(5) 8, c = 25.21(2) 8, a = 90.0" p = 90.0" x = 90.0" V = 1689.3(6) 8,3
Space group
~12121 Orthorhombic
Moleculedunit cell
4
Density observed, g/cm3
1.37
Density calculated, g/cm3
1.354
Linear absorption coefficient
49.48
465
BRUCE M . JOHNSON AND PEI-TEI L. CHANG
466
CI
Figure 9. Single Crystal X-Ray Structure of Sertraline HCl (Form I)
SERTRALINE HYDROCHLORIDE
461
4.13. Polymorphism Five crystalline polymorphic forms of sertraline hydrochloride have been isolated and ~haracterized.'~ Four of the polymorphs have been examined by infrared absorption spectroscopy, X-ray powder diffraction, single crystal X-ray, differential scanning calorimetry (DSC), hot stage optical microscopy, and aqueous solubility studies. Only a few crystals of the fifth polymorph have been isolated and the only characterization data available are from single crystal X-ray studies and infrared spectra. The polymorphs of sertraline hydrochloride have been designated as Forms I, 11, 111, IV, and V. Form I represents the lower melting polymorph which may crystallize from an acidic solution of the compound in isopropyl alcohol, hexane, or ethyl acetate depending on temperature and rate of crystallization. Forms 11 and IV are metastable polymorphs which can be isolated by rapid crystallization of sertraline hydrochloride from various solvents (e.g., methanol, ethyl acetate, acetonitrile); however, slow crystallizations and granulations yield polymorph Form I. Form 111 is generated from Forms I, 11, or IV by heating the solid to temperatures above about 180°C. Granulating either Form 11, 111, or IV in isopropanol, ethyl acetate, or hexane at 40 to 60°C causes conversion to Form I. Form V is produced by sublimation of Form I onto a cold finger condenser. Form I is the thermodynamically most stable polymorph at room temperature. The following information summarizes observations concerning the characterization, stability, and thermal behavior of sertraline hydrochloride polymorphs. 4.13.1. Characterization Data Infrared Absorption Spectrophotometq The infrared absorption spectra of Forms I, 11, 111, IV,and V are different from one another (Figure 10). The spectra are obtained using KBr pellets to suspend the sample during
468
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
measurement. Figure 10 displays only the region of 1650 to 400 cm-1. The region from 4000 to 1650 cm-1 is not useful for comparing polymorphic differences. Qualitative comparison of the infrared spectra of Form I to Forms 11, 111, IV, and V show the following differences: a. At approximately 740 to 750 cm-l and 1075 to 1085 cm-1 Forms 11, 111, IV, and V exhibit absorption bands of significantly higher relative intensity. b. At approximately 780 cm-l Forms 11, 111, and IV exhibit major peaks. Forms I and V exhibit a major peak at approximately 790 cm-1with only a shoulder at about 780 cm-1. c. Forms 11, 111, IV, and V show absorption bands at approximately 870 and 520 to 540 cm-1 while no absorption is observed for Form I at these wavelengths. d. Form 11 shows a strong absorption band and Forms 111, IV, and V a weak band at about 640 cm-l, while a barely detectable absorption is observed for Form I.
e. Differences for Forms 11, 111, and IV are also observed in wavelength and relative intensity of the absorption bands in the region of 800 to 850 cm-1 compared to Forms I and V. Single Crystal X-Ray Analysis Absolute structure determination of Forms I, 11, HI, IV, and V by single crystai X-ray analysis shows that the polymorphic forms differ in rotational conformation at the methylamino and the dichlorophenyl positions. Forms 111and IV are similar rotationally but differ in their space group. Using these configurations the crystal packing diagrams are constructed and the crystal densities are calculated. Form I gives a density of 1.354 gkc, Form I1 gives a density of 1.314 g/cc, Form 111gives a density of 1.3 13 g/cc,
z T
I
a
n S
m I
t t
a n C 8
-120
4
Y 1600
1500
1400
1300
1200
1100
1mo
900
800
700
600
Figure 10. Infrared Spectra of Sertraline HCl Polymorphs (Wavelength range 1650 to 400 cm-1)
500
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BRUCE M. JOHNSON AND PEI-TEIL. CHANG
Form IV gives a density of 1.349 g/cc, and Form V gives a density of 1.308 g/cc. This result supports Form I as the thermodynamically stable form at room temperature since the most dense crystal at a given temperature is considered to be the most thermodynamically stabiei5. Using these single crystal data it is possible to calculate the theoretical powder diffraction patterns. The theoretical patterns shown in Figure 1 1 for Forms I, II, III, and IV match the observed patterns very closely. X-Ray Powder Diffraction The four polymorphs of sertraline hydrochloride for which samples are available give distinctive X-ray powder diffraction patterns. Each form has diffractions at unique values of 28 that are diagnostic: Form1
7.1, 12.7, 14.1, 15.3, 15.7,21.2,23.4, and26.3
Form11
5.4, 10.8, 14.6, 16.3, 18.1, 19.0,20.3,21.8, 24.4, and 27.3
FormIII
14.3, 15.5, 17.4, and 19.6
Form IV
15.6,22.4,25.4,28.9,31.9,and 32.1
In these powder diffraction patterns of the pure polymorphs, each of the unique peaks is greater than about 10%of the normalized intensity. In normal practice the 28 values remain constant but the relative intensities may vary somewhat due to particle size effects. Figure 1 1 shows the powder diffraction patterns calculated from the single crystal data. The pattern for Polymorph V is also included here and shows a distinctive pattern as well.
SERTRALINE HYDROCHLORIDE
47 1
POLYHORPH I
Figure 11. Calculated X-Ray Powder Diffraction Patterns 4.13.2. Relative Stability of Sertraline Hydrochloride Polymorphs Interconversion Experiments
Forms 11and TV have been made by rapid crystallization out of solvents and Form 111has been made by heating a sample of Form I at about 180°C for a period of several hours. When mixtures of Form I and Forms 11, 111, or IV were granulated in isopropyl alcohol at 50°C, the resulting solid was shown to be Form I. Similar behavior has been observed in other solvents. In an experiment viewed under the microscope at room temperature, a mixture of Forms I, 11, and 111was placed on a slide
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BRUCE M. JOHNSON AND PEI-TEI L. CHANG
and covered with a cover slip. Isopropanol saturated with sertraline hydrochloride was added at the edge of the cover slip and the sample was kept wet with solvent throughout the observation. Crystals of Form III disappeared fairly rapidly. Crystals of Form II shrunk in size slowly while the Form I crystals increased in size. In a similar experiment with Forms I and IV,Form IV dissolved slowly while Form I grew. These observations are consistent with the greater thermodynamic stability of Form I. Solubility The room temperature aqueous solubility of the four polymorphs is essentially equivalent at about 4 m u d . Polymorphs 11,III, and IV appear to be slightly more soluble than Form I, further indicating that Form I is the most stable at room temperature. 4.13.3. Thermal Behavior
Differential Scanning Calorimetry CDSC) The DSC thermograms for Forms I - IV are shown in Figures 12, 13, 14, and 15. The features in the thermograms may be interpreted as follows:
Form I shows an endotherm with an onset temperature of about 219°C resulting from the melting of Form I. An exotherm immediately following the melting endotherm of Form I appears at about 225°C caused by partial crystallization of the melt to Form III, and a second endotherm appears with an onset at about 246°C resulting from the melting of Form III. Rapid thermal decomposition takes over after the final melt of Form III causing the baseline to increase rapidly and become erratic in appearance. On rare occasions, the DSC of Form I shows only a single melting endotherm with an onset temperature of about 219°C. This can occur when the sample does not have sufficient time or seed to
SERTRALINE HYDROCHLORIDE
413
recrystallize as Form 111prior to reaching the Form 111melting temperature.
In the thermograms obtained for Forms 11and IV,a very small endotherm may be observed with an onset temperature at about 180°C which corresponds to a solid-solid transition to Form 111. This event is followed by melting of Form 111at about 246°C. The thermogram obtained for Form 111 shows a single endotherm at about 246°C. Above the melting temperature of 246" C thermal decomposition increases rapidly. The thermal events discussed above demonstrate that Form 111undergoes only a single melting process at 246°C followed by increased thermal decomposition after the melt has occurred. Thermogravimetry and hot stage optical microscopy reveal that all four forms undergo slight decomposition and sublimation at temperatures above about 160°C. Prolonged heating studies on the Form Worm 111 conversion in the solid state have shown that below 160°C Form I is the preferred polymorph. Above 180°C Form I converts to Form 111in the solid state. This conversion takes place at varying rates in the DSC experiment depending on sample characteristics such as particle size, previous handling, or the presence of Form III seed. Thus, in some instances the first endotherm in Form I may show a smaller endotherm with a lower onset temperature as a result of solid state conversion of Form I to Form 111during heating. The solid state conversion is a very low energy transition and fails to give a reliably detectable DSC event. A sample of Form I spiked with 3% of Form 111(Figure 16) shows an endotherm for the solid state transition and the absence of the Form I melting endotherm. The Form 111endotherm appears at the expected temperature of about 246°C. Under the conditions of this DSC experiment the solid state transition is fast enough to cause complete conversion to Form 111before the Form I melt temperature is reached. Similar
BRUCE M.JOHNSON AND PEI-TEI L.CHANG
474 01
Figure 12. DSC Thermogram of Sertraline HCl Form I)
u
I V
c
m
aa
Figure 13. DSC Thermogram of Sertraline HCl (Form II)
SERTRALINE HYDROCHLORIDE
415
I
Figure 14. DSC Thermogram of Sertraline HCl (Form III)
Figure 15. DSC Thennogram of Sertraline HCl (Form IV)
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
476 LOO
U
s
LSD
-I
0.w
Figure 16. DSC Thermogram of Sertraline HCl (Form I containing 3% of Form 111) behavior was observed in two other samples of Form I spiked with 5% of Form I1 or 5% of Form IV.
In a related experiment, small amounts of each of Forms I, 11, and IV were heated to 185°C for 15 minutes. The infrared spectra of each sample confmed that they had converted to Form 111. Hot Stage Optical Microscopy Microscopic observation of a Form I sample heated on a hol stage is consistent with the observed DSC behavior. At about 150 to 180°C the sample begins to move about and appears to "pop". This may be caused by the onset of decomposition, solvent release, or sublimation. Partial melting may be observed at about 210 to 220°C with the formation of some new crystals (Form 111) as the temperature is raised to about 235°C. (In some instances, a solidsolid transition to Form I11 is observed at temperatures above about
SERTRALINE HYDROCHLORIDE
411
180°C.) At about 245 to 250°C the newly formed crystals melt completely. The melt solidifies very slowly upon cooling and usually remains as a yellowish glass. This suggests that significant decomposition has taken place. In mixtures of Form I11 in Form I, the first melt at 210 to 220°C does not cause all of the sample to liquefy, a small number of crystals may remain and increase in size as Form 111crystallizes around them. Holding the temperature at about 235°C permits the melt to recrystallize to Form III. Cooling this melt to room temperature and subsequent reheating does not show the Form I melt at 210 to 220°C. This suggests that the conversion to Form 111is not rapidly reversible under these conditions. Microscopic observation of Forms 11or IV on the hot stage shows an apparent solidkolid transition at about 180°C without evidence of melting. Continued heating gives a complete melt at about 245°C. The temperature region of 180 to 230°C appears also to cause decomposition and sublimation. Microscopic observation of Form 111 shows sample movement similar to Form I at about 160°C followed by melting at about 245 to 250°C. No other thermal events are seen and the observation is consistent with the DSC behavior. When samples are heated in silicone oil the appearance of gas bubbles is observed starting at around 150 to 180°C suggesting the onset of decomposition. The yellowish color of the melt above 250°C results from chemical decomposition of the sample. This phenomenon occurs for all four polymorphic forms.
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
47%
4.13.4. Literature Precedent Polymorphs of sertraline hydrochloride behave similarly to those of gepirone hydrochloride which has been characterized and discussed in the 1iteraturel6. Both compounds have a polymorph which is most thermodynamically stable at room temperature which can go through an endothermic melt and subsequently recrystallize as a higher melting polymorph.
5.
Methods of Analysis 5.1.
Elemental Analysis
The elemental composition of sertraline hydrochloride was determined by a series of microanalytical determinations. A typical set of analyses is shown below. Assay % carbon % hydrogen % nitrogen % chlorine, ionic % chlorine, total
Total (C,H,N,Cl)
59.54 5.30 3.85 10.24 30.54 99.23
59.58 5.29 4.09 10.35 31.04 100.00
The results for percentage carbon, hydrogen, nitrogen, and chlorine for sertraline hydrochloride are consistent with the theoretical values for the formula C17HIgNC13. 5.2.
Ionic Chlorine
The ionic chlorine content of sertraline hydrochloride may be determined by potentiometric titration with a standard silver nitrate solution, which precipitates the chloride ion as AgC1. Titration is carried out by dissolving the sertraline hydrochloride in ethanovwater (1: 1, v/v) and titrating using a silver measuring electrode and a Ag/ AgCl reference electrode. The theoretical ionic
SERTRALINE HYDROCHLORIDE
479
chloride content of sertraline hydrochloride is 10.35%;the amount found for the reference standard lot was 10.24%.
5.3.
Identification
Sertraline hydrochloride is identified in the bulk form using the infrared spectrum, the TLC retention, and the HPLC retention by comparison with a working standard. In dosage forms the TLC retention and the HPLC retention are used for confirming identity of drug substance.
5.4.
Thin Layer Chromatography
Thin layer chromatography is used as a technique for establishing the identity of sertraline and for examining for the presence of process related substances and other potential impurities. The following systems have been used with silica gel 60 F-254 (Merck Darmstadt) plates. Solvent System
Rf
Detection
Ethyl acetate/Methanol/Ammonium acetate 160:40:2 v/v
0.55
1
Chloroform
0.00
2
Chloroform/Methanol/ammoniumacetate 12050:15 v/v
0.91
2
Detection Systems 1 2
5.5.
Dragendorff's Reagent Ultraviolet light - 254 nm
Ultraviolet Spectroscopy
Assay for sertraline content of drug substance and drug products may be carried out using ultraviolet spectrophotometry.
BRtiCE M. JOHNSON AND PEI-TEI L. CHANG
480
Sertraline solutions are prepared in 0.01 N methanolic hydrochloric acid at a concentration of approximately 0.05 mg/mL. Absorbance measurements are taken at 273 nm and compared to the absorbance of a well characterized standard.
5.6.
Potentiometric Titration
Being a hydrochloride salt, sertraline hydrochloride has an acidic proton which can be titrated with 0.5 N aqueous sodium hydroxide in the solvent mixture ethanovwater, 1:1, v/v. When 98.67 mg of sertraline hydrochloride reference standard was titrated in 20 mL of the solvent mixture, a single inflection point was observed. This was attributed to the single acidic proton located on the arnine nitrogen of the sertraline hydrochloride molecule. The neutralization equivalent (molecular weight) calculated for the single inflection point was 345.5. Based on this result, an assay of 89.3% sertraline was calculated for the reference standard lot, which is 99.9% of theory (89.4%). This titrimetric result confirms the stoichiometry of sertraline hydrochloride and provides an equivalent weight value consistent with the structure. A representative curve for this titrimetric procedure is included in Figure 17.
5.7.
High Performance Liquid Chromatography
Purity assay of sertraline hydrochloride is done using HPLC by the external standard method by comparing chromatographic response with a well characterized standard. An isocratic reverse phase system using a C-18 column and UV detection at 254 nm is suitable for both drug substance and formulated products. Column: Detector: Mobile Phase: Buffer:
Waters Nova-Pak C- 18 UV at 254 nm
Acetonitrile/MethanoYSuffer 45: 15:40 v/v 0.05 M Acetic acid/O.OZ M Triethylamine (aqueous)
SERTRALINE HYDROCHLORIDE
481
PH
0 -
9 1 2 3 4 6 6 7 8 P 1 9 1 1 1 2 1 1 1 4 1 1 1 1 l l 1 1 1 1 l l l l 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
0.10
0.20
0.30
-
-
0.40 mL
-
0.60
-
0.60
-
0.70
-
0.80
-
Figure 17. Potentiometric Titration of Sertraline HCl in EthanoVWater (1:l)
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
4x2
Metabolic studies have used HPLC to measure sertraline and its metabolites in urine, bile, and feces using radiolabeled drug17 and a radioactivity detector and/or a variable wavelength UV detector’*. Two different mobile phases were reported. Column: Waters C - 18 pBondapak Berthold radioactivity monitor or UV Detector: Mobile Phase 1 : Acetonitrile/SO mM Sodium phosphate (pH 4.5) 5050 v/v Mobile Phase 2: AcetoniUilelSO mM Ammonium acetate (pH 5.0) 33167v/v
Another HPLC method has been reported for measuring sertralirie and desmethylsertraline in mouse cerebral cortex using an internal standard method”.
Column: Detector: Mobile Phase:
5.8.
Versapack C- 18 UV at 235 nm Acetonitrile/0.25 M Potassium phosphate (pH 2.7) 30:70 v/v
Gas Liquid Chromatography
Gas liquid chromatography is used to separate sertraline from its process related substances, in particular the dechlorinated homologs. Hydrochloride salts are converted to their free base form by extraction of a basified solution into methylene chloride prior to injection. The following system has been used for the drug substance. Column:
Column Temp: Injector Temp: Detector Temp: Detector:
5% OV-17 on Chromosorb W (acid washed and DMCS treated) packed in a 7 ft. x 0.25 in. OD glass column 225°C 250°C 300°C Flame ionization
SERTRALINE HYDROCHLORIDE
483
Gas chromatography has also been used to measure sertraline levels in biological fluids. The drug is extracted from plasma and derivatized with trifluoroacetic anhydride. The derivative is chromatographed using either a mass spectrometric detector2' or a 63Ni electron capture detector21. GCMS Method Column: 3% Silar 1OC on Gas Chrom Q (80 - 100 mesh) packed in a 0.8 m x 2 mm ID glass column Column Temp: 255°C Injector Temp: 200°C Transfer Temp: 290°C Detector: Mass spectrometer Electron Capture Method Column: SE-54,0.25 pm film thickness, 12 m x 0.32 mm ID capillary column Column Temp: 165°C for 0.5 min, 20"C/min to 21OoC, hold for 12 min Injector Temp: 260°C Detector Temp: 300°C Detector: 63Ni Electron Capture
5.9.
Biological Fluids
The levels of sertraline and its major metabolites are measured in biological fluids by HPLC, GC/EC, and GCMS using the methods described above. Metabolism studies have resulted in the identification of N-desmethylsertraline, sertraline carbamoyl-0glucuronide, N-hydroxysertraline, a ketone [4-S-(3,4dichlorophenyl)-3,4-dihydro-1(2H)-naphthalenone], and the ahydroxyketone [4-S-(3,4-dichlorophenyl)-3,4-dihydro-2-R,Shydroxy-1(2H)-naphthalenone] as well as the glucuronides of Nhydroxysertraline and the a-hydroxyketone2*.
BRUCE M. JOHNSON AND PEI-TEI L. CHANG
484
6.
Stability The stability of sertraline hydrochloride has been studied under extreme challenge conditions as well as the more traditional pharmaceutical challenge conditions. The extreme conditions included exposing excess drug substance to refluxing water for 3 hours, refluxing 5 N hydrochloric acid for 3 hours, refluxing 5 N NaOH for 3 hours, or 10% hydrogen peroxide for 6 hours. The more traditional stability challenge conditions of 3 months at 50°C, 12 months at 37"C, 60 months at 30°C, or 3 months in a light cabinet were used with different packaging systems. Careful examination of the resulting samples revealed no significant degradation under any of the conditions used in these studies. The only trace degradation product identified was the ketone [4-S-(3,4dichlorophenyl)-3,4-dihydro-1(2H)-naphthalenone] which has also been identified as a metabolite. Sertraline hydrochloride appears to be a very stable compound under a variety of challenge conditions.
7.
Pharmacokinetics and Metabolism 7.1.
Systemic Bioavailability
In man, following oral once-daily dosing of sertraline hydrochloride (Form I) over the range of 50 to 200 mg for 14 days, mean peak plasma concentrations (C,) of sertraline occurred between 4.5 to 8.4hours postdosing. The average terminal elimination half-life of plasma sertraline is about 26 hours. Based on this pharmacokinetic parameter, steady-state sertraline plasma levels should be achieved after approximately one week of oncedaily dosing. Linear dose-proportional pharmacokinetics were demonstrated in a single dose study in which the C, and area under the plasma concentration time curve (AUC) of sertraline were proportional to dose over a range of 50 to 200 mg. Consistent with the terminal elimination half-life, there is an approximately two-fold accumulation, compared to a single dose, of sertraline with repeated dosing over a 50 to 200 mg dose range. The single dose bioavailability of sertraline tablets is approximately equal to an equivalent dose of solution23.
SERTRALINE HYDROCHLORIDE
485
The effects of food on the bioavailability of sertraline were studied in subjects administered a single dose with and without food. AUC was slightly increased when drug was administered with food but the C, was 25% greater, while the time to reach peak plasma concentration decreased from 8 hours post-dosing to 5.5 hours. 7.2.
Metabolism
Sertraline undergoes extensive first pass metabolism. The principal initial pathway of metabolism for sertraline is Ndemethylation. N-desmethylsertraline has a plasma terminal elimination half-life of 62 to 104 hours. Both in vitro biochemical and in viva pharmacological testing have shown Ndesmethylsertraline to be substantially less active than sertraline. Both sertraline and N-desmethylsertraline undergo oxidative deamination and subsequent reduction, hydroxylation, and glucuronide conjugation. In a study of radiolabeled sertraline involving two healthy male subjects, sertraline accounted for less than 5% of the plasma radioactivity. About 40-45% of the administered radioactivity was recovered in urine in 9 days. unchanged sertraline was not detectable in the urine. For the same period, about 40-45% of the administered radioactivity was accounted for in feces, including 12-14%unchanged sertralineZ4. Desmethylsertraline exhibits time-related, dose dependent and Cmin, with about a 5-9 increases in AUC (0-24 hour), C, fold increase in these pharmacokinetic parameters between day 1 andday 14.
Acknowlegement The authors wish to thank our many Pfizer colleagues in the Central Research laboratories in both Groton, CT, USA and Sandwich, Kent, UK who have contributed to the development of sertraline hydrochloride and to the information presented in this overview.
486
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BRUCE M.JOHNSON AND PEI-TEI L. CHANG
'Koe, B. K.; Weissman, A.; Welch, W. M.; Browne, R. G. J. Exp. Ther. 1983,226, 686. 2Package Insert, Zoloft*, Pfizer Inc, Jan. 1992 3Quallich, G. J.; Williams, M. T. U.S. Patent 4 777 288, 1988. 'Quallich, G. J.; Williams, M. T. U.S. Patent 4 839 104, 1989. 5Williams, M. T.; Quallich, G. J. Chemistry and Industry 1990,21, 315. 6Adrian, G. P. U.S. Patent 5 019 655,1991. 'Quallich, G. J.; Williams, M. T. European Patent 0 295 050 A l , 1988. 'Quallich, G . J.; Williams, M. T.; Friedmann, R. C. J. Org. Chem. 1990,55,4971. w e l c h , W. M.; Kraska, A. R.; Sarges, R.; Koe,B. K. J. Med. Chem. 1984,27, 1508. '()Welch, Jr., W. M.; Harbert, C. A.; Koe, B. K.; Kraska, A. R. U.S. Patent 4 536 518, 1985. "Ewing, D. F. Organic Magnetic Resonance 1979, 12(9), 499. 12 Sharp, T. R.; Horan, G. J.; Day, S.V.O. Proceedings of the 41st ASMS Conference 01 Mass Spectrometry and Allied Topics, San Francisco, California, 1993. I3Clarke, F. H.; Cahoon, N. M. J. Pharm. Sci. 1987,8,611. '*Sysko, R. J.; Allen, D. M. J. US.Patent 5 248 699, 1993. "Haleblian, J.; McCrone, W. J. Pharm. Sci. 1969,58(8), 911. %ehme, R. J.; Brooke, D.; Farney, R. F.; Kensler, T. T. J. Pharm. Sci. 1985, 74(10), 1041. "Welch, W. M.; Vivieros, D. M. J. Labelled Compd. Radiopkam. 1987, 24, 987. 18 Tremaine, L. M.; Stroh, J. G.; Ronfeld, R. A. Drug Metab. Dispos. 1989, 17,58. 'weiner, H. L.; Kramer, H. K.; Reith, M. E. A. J. Chromatog. 1990,527,467. 2%ouda, H. 6.; Ronfeld, R. A.; Weidler, D. J. J. Chromatog. 1987,417, 197. "Tremaine, L. M.; Joerg, E. A. J. Chromatog. 1989,496,423. 2?remaine, L. M.; Welch, W. M.; Ronfeld, R. A. Drug Metab. Dispos. 1989, 17, 542. 23PackageInsert, Zolofi@,Pfizer Inc, Jan. 1992 24 Package Insert, Zoloft@, Pfizer Inc, Jan. 1992