Pseudoephedrine Hydrochloride

Analytical Profiles of Drug Substances, 8

PSEUDOEPHEDRINE HYDROCHLORIDE Steven A . Benezra and John W . McRae 1.

2.

3. 4. 5. 6.

Description 1.1 Name, Formula, Molecular Weight 1.2 Appearance, Color, Odor Physical Properties 2. I Infrared Spectrum 2.2 Nuclear Magnetic Resonance Spectrum 2.3 Ultraviolet Spectrum 2.4 Mass Spectrum 2.5 Melting Point 2.6 Specific Rotation 2.7 Solubility 2.8 Partition Coefficient 2.9 Differential Scanning Calorimetry 2.10 Crystal Structure 2.1 I Dissociation Constant Synthesis Stability Metabolism and Pharmacokinetics Methods of Analysis 6.1 Elemental Analysis 6.2 Nonaqueous Titration 6.3 Ultraviolet Spectrophotometric Analysis 6.4 Colorimetric Analysis 6.5 Chromatography 6.51 High Performance Liquid Chromatography 6.52 Thin-Layer Chromatography 6.53 Paper Chromatography 6.54 Gas Chromatography

489

Copyright @ 1979 by Academic Press, Inc. All rights of reproduction in any form reserved. ISBN 0-12-260808-9

490

1.

STEVEN A . BENEZRA AND

JOHN W. MCRAE

Description

1.1 Name, Formula, Molecular Weight d-Pseudoephedrine hydrochloride is (+)-threo-a-(1(methy1amino)ethyl)benzyl alcohol hydrochloride. Throughout this analytical profile, d-pseudoephedrine will be referred to as pseudoephedrine.

*o

C10H15NO*HC1

H

0

HCI

I

CH3

201.72

1.2 Appearance, Color, Odor Pseudoephedrine hydrochloride occurs as fine white t o off-white crystals o r as a powder having a faint odor1

2.

Physical Properties

2.1 Infrared Spectrum The infrared spectrum of pseudoephedrine hydrochloride is shown in Figure 1. It was obtained as a 0.2% dispersion of pseudoephedrine hydrochloride in KBr with a Nicolet Model 7199 FT-IR spectrophotometer.2 Table I gives the infrared assignments consistent with the structure of pseudoephedrine hydrochloride. Table I Infrared Spectral Assignments for Pseudoephedrine Hydrochloride Frequency (cm-l) Assignment OH stretch 3270 3010 Asym. C-H stretch

1

0

0

1

1

8

1

I

3

I

I

0 d

1

0 (u

STEVEN A. BENEZRA AND

492

Sym. C-H stretch

2930

+NH

2700

stretch

C=C aromatic stretch OH bend, secondary alcohol C-H bend, monosubst. benzene

1587, 1490 1430 762, 702 2.2

JOHNW. MCRAE

Nuclear Magnetic Resonance (NMR) Spectrum The NMR spectrum o f pseudoephedrine hydrochloride

is shown in Figure 2.

The spectrum was obtained with a

Varian model CFT-20 80 MHz NMR spectrometer. Deuterated DMSO was used as the solvent with tetramethylsilane as an internal standard. Table I1 gives the NMR assignments consistent with the structure of pseudoephedrine hydrochloride.

G9

8 H H HN-

OH H

@@

Table I1

NMR Assignments for Pseudoephedrine Hydrochloride Proton a

No. of Protons 3

Shift (ppm) 0.96

Multiplicity doublet

b

3

2.55

singlet

C

1

3.25

quartet (partially obscured by H20)

d

1

e

1

f

5

8

2

4.54 6.32 7.34 8.90

doublet of doublets doublet singlet broad singlet

493

PSEUDOEPHEDRINE HYDROCHLORIDE

J

1

1 I

8

9

Figure 2

-

7

6

5

4

3

S

I

2

'

I

!

I

1

I

1

I'

0

PPm

NMR Spectrum of Pseudoephedrine Hydrochloride

I.o

ae

0.6 U

4 [L

v 0 )

a 0.4

0.2

0.9

Figure 3

-

nrn

Ultraviolet Spectrum of Pseudoephedrine Hydrochloride

STEVEN A. BENEZRA A N D

494

JOHN W. MCRAE

2.3 Ultraviolet Spectrum The ultraviolet spectrum of pseudoephedrine hydrochloride in ethanol was obtained with a Beckman ACTA CIII ultraviolet spectrophotometer and is shown in Figure 3. Pseudoephedrine hydrochloride exhibits absorption maxima at 208, 251, 257, and 264 nm with extinction coefficients of 8300, 161, 201, and 161, respectively. 2.4. Mass Spectrum The low resolution mass spectrum of pseudoephedrine hydrochloride is shown in Figure 4.5 It was obtained with a Varian MAT CH5-DF mass spectrometer. Direct probe at 80'C into the ion source was used to obtain the mass spectrum. The electron energy was 70 eV. The assignments of the major ions formed in the mass spectrometer are shown below.

The

molecular ion is not observed.

H +HC/NzCH3 'CHq3 m/e 58 (100%) 2.5

0 +

m/e 77 (9%)

HCI

m/e 36 (10%)

+

HNCH3

m/e 30 (12%)

Melting Point Pseudoephedrine hydrochloride melts between 182'

and 185'C.

2.5 Specific Rotation The specific rotation, of d-pseudoephedrine hydrochloride in water is between +61.0' and +62.5'.l

[cy]iO,

2.7

Solubility The solubility of pseudoephedrine hydrochloride in

495

PSEUDOEPHEDRINE HYDROCHLORIDE

1001

I50

I00

200

m /e

Figure 4

1 I

178

-

Mass Spectrum of Pseudoephedrine Hydrochloride

1

1

179

180

1 I

181

I

I

182

1 1

183

TEMPERATURE

Figure 5

-

1

i

184

I

1

185

1 1

186

1

1

187

OC

DSC Curve of Pseudoephedrine Hydrochloride

STEVEN A. BENEZRA AND JOHN W. MCRAE

496

various solvents at 25OC is given in Table 111.' Table I11 Solubility of Pseudoephedrine Hydrochloride at 25OC Solvent

Solubility (gm/ml)

Water

2.0

Chloroform

0.011

E thano1

0.278

Ether

1.4

2.8 Partition Coefficient The partition coefficients of pseudoephedrine hydrochloride at 25OC in n-octanol/aq. pH 1.2 and n-octanol/ aq. pH 6.0 are 0.010 and 0.049 respectively.6 2.9 Differential Scanning Calorimetry (DSC) The DSC curve of pseudoephedrine hydrochloride obtained with a Perkin Elmer DSC-1B differential scanning calorimeter is shown in Figure 5 . ?

The heating rate was

5OC/min. The heat of fusion is 6.4 Kcal/mol. The melting point (uncorrected) is 184OC. 2.10 Crystal Structure The crystal properties of pseudoephedrine hydrochloride were determined with a GE model XRD-6 x-ray diffractometer using Zr filtered MoKa radiation on a crystal grown from water.

Pseudoephedrine hydrochloride has an ortho-

rhombic crystal system belonging to the P2 2 2 space group. 0 l a 1 0 The cell dimensions are a=25.358 A , bz6.428 A , ~ ~ 6 . 9 0A1 with each cell containing four molecules. 2.11 Dissociation Constant The pKa of pseudoephedrine hydrochloride determined

PSEUDOEPHEDRINE HYDROCHLORIDE

491

titrimetrically in 80% aqueous methylcellosolve is 9.22. 3.

Synthesis Pseudoephedrine hydrochloride is prepared by a

Welsh rearrangementl o of R-ephedrine hydrochloride with acetic anhydride followed by deacetylation with hydrochloric acid. l 1

2-Ephedrine can be resolved from dR-ephedrine with

2-mandelic acid. l2

R-Ephedrine occurs naturally in certain

plants of the Ma Huang species. 4.

Stability Pseudoephedrine hydrochloride can be considered a

stable compound in bulk and in formulations. After 4-weeks under fluorescent lights (2400 ft. candles) and ultraviolet light (190 pw/cm2) no discoloration or chemical degradation was observed. The bulk drug was stable for at least 6 months at 37OC and 3 months at 5OoC. Tablet and syrup formulations stored at 15-30°C for 5 years showed no appreciable degradation. l 3

5.

Metabolism and Pharmacokinetics The major biotransformations of pseudoephedrine

hydrochloride are parahydroxylation, N-demethylation, and oxidative deamination. l4

The proposed pathways for the

metabolism of pseudoephedrine are shown in Figure 6 . In a study with human subjects, whose urine pH was controlled with sodium bicarbonate and ammonium chloride, it was found that 10-25% of the administered pseudoephedrine hydrochloride was metabolized to norpseudoephedrine and the elimination of pseudoephedrine and norpseudoephedrine was related to urine pH.

As the urine pH increased, the serum

half-life o f pseudoephedrine and norpseudoephedrine increased.15

In another similar study it was found that a decrease

H

CH3

p-&-H++-Q

\ I

OH NH I

CH3 Pseudoephedr ine

Nor pseudoephedrine

o + ( / OH

I/

OH NH,

CH3

I-Hydroxy-l-phenyl-2-proponone

OW,H OH OH

I -Phenyl-l,Z-propanediol

OH Benzoic acid Figure 6

-

Metabolism of Pseudoephedrine Hydrochloride

PSEUDOEPHEDRINE HYDROCHLORIDE

499

in urine pH caused a decrease in plasma half-life of pseudoephedrine. l6

Plasma half-lives measured in normal human

subjects were 5 . 2 - 8 . 0 hours.l6 In a rat study using 14C-labelled dQ-ephedrine, 85% of the i.p.-administered drug was eliminated in the first 40 hours.

Two major metabolic pathways were postulated after

analysis of the metabolites. The major metabolic pathway was ring para-hydroxylation forming para-hydroxyephedrine and para-hydroxynorephedrine.

The minor metabolic pathway was

oxidative deamination, giving acidic metabolites such as hippuric and benzoic acids. l7 The relative tissue distribution in mice 15 minutes after i.v.-administered l4C2ephedrine was kidney > lung, adrenal, spleen, liver > intestines, stomach > brain, heart > plasma. l7 The LDs0 in mice o f pseudoephedrine administered i.p. is 1.0 mmole/kg.18 6.

Methods of Analysis 6.1

Elemental Analysis

The results of the elemental analysis o f pseudoephedrine hydrochloride are given in Table IV.6 The analysis was performed on a NF Reference Standard. Table IV Elemental Analysis of Pseudoephedrine Hydrochloride Element

Theory (%)

Found ( X )

C

59.55

59.54

H

8.00

8.11

N

6.95

6.81

STEVEN A. BENEZRA AND

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6.2

JOHN W.M C W E

Nonaqueous Titration Pseudoephedrine hydrochloride is dissolved in a

mixture of glacial acetic acid and mercuric acetate test solution. A standardized solution of 0 . 1 N perchloric acid is used to titrate the solution to a blue-green end point with crystal violet indicator. Each ml of 0.1N perchloric acid is equivalent to 0.1 mmole of pseudoephedrine hydrochloride. 6.3

Ultraviolet Spectrophotometric Analysis An ultraviolet spectrophotometric analysis is used

to assay pseudoephedrine hydrochloride in tablets. A portion of finely powdered tablets equivalent to approximately 30 mg of pseudoephedrine hydrochloride is placed in a distilling flask which is part of a micro-steam distillation apparatus. Sodium chloride, water, and concentrated sodium hydroxide are added. A minimum of 30 ml of distillate is collected in a volumetric flask containing dilute hydrochloric acid.

The

flask is made to volume with distilled water and the absorbance of the solution is determined at 257 nm in 1 cm cells and compared to a solution of known concentration of NF Pseudoephedrine Hydrochloride Reference Standard. An ultraviolet spectrophotometric method based on the absorbance of a periodate oxidation product o f pseudoephedrine hydrochloride will be the official method of analysis in the USP XX.19,20 A portion of tablets or syrup in water is placed in a separatory funne.1. Sodium bicarbonate and sodium metaperiodate are added. After standing for 15 minutes, 1 N HC1 is added. The solution is extracted with hexane. The hexane extract is filtered and its absorbance determined at 242 nm in 1 cm cells. The amount of the oxidation product of pseudoephedrine hydrochloride is determined by comparison of the sample absorbance against the absorbance of a Pseudoephedrine Hydrochloride Reference Standard treated in the same manner.

50 1

PSEUDOEPHEDRINE HYDROCHLORIDE

6.4 Colorimetric Analysis Pseudoephedrine hydrochloride in syrup formulations has been analyzed by colorimetry. Pseudoephedrine forms a stable blue-colored chelate with cupric sulfate at pH 12.5. The complex has a maximum absorbance at 500 nm. The complex is extracted from an aqueous layer with 1-pentanol. Interfering substances such as glycerine and sugars normally found in syrup formulations, which form complexes with cupric aulfate, are not extracted into l-pentanol.*l 6.5

Chromatography 6.51 High Performance Liquid Chromatography (HPLC) High performance liquid chromatography has been

used to analyze pseudoephedrine hydrochloride and dosage forms containing pseudoephedrine hydrochloride.

Table V

gives the HPLC conditions used for separations. Table V HPLC Conditions €or Pseudoephedrine Hydrochloride Column Corasil@/Phenyl

Mobile Phase Rention Time (min) 1.8 (phenyl) acetonitrile:

Corasil@/C18

0.1% ammonium

Reference 22

1.9 (C18)

carbonate (9:l) pH 8.9

Corasil@/Phenyl Corasil@/C18

acetonitrile: 1% ammonium

carbonate (6:4) pH 7.4

22

STEVEN A. BENEZRA AND JOHN W.M C M E

502

Zipax@/SCX

0.02 M dibasic ammonium phosphate:dioxane

7

23

6

24

8

25

(64:36) Nucleosil@/

methanol:0.5M

silica gel

sodium dihydrogen phosphate: phosphoric acid (195:50:2)

Spherisorb@/

ethanol:0.4%

silica gel

ammonium acetate (85: 15)

6.52 Thin Layer Chromatography (TLC) Table VI lists the various TLC systems used for pseudoephedrine hydrochloride. Table VI TLC Systems for Pseudoephedrine Hydrochloride

Rf

Reference

silica gel

0.25

26

silica gel

0.46

Mobile Phase

Adsorbent

ethyl acetate: cyclohexane: methano1:conc. M140H(70:15:10:5) n-butano1:ethanol: water:acetic acid (60:30:10:0.2)

27 0.18 (free base)

PSEUDOEPHEDRINE HYDROCHLORIDE

chlorof o rni:

silica gel

503

0.33

28

methanol : acetone (7:3:5) ethyl ether:

0.10 (free base) silica gel

benzene (1:l)

0.35 (as 4-chloro-

29

7-nitrobenzo-2,1,3oxadiazole derivative) chloroform :

alumina

0.70 (as

water:acetic

acetylated

acid (20:75:20:1)

product)

16

(lower phase) 6.53 Paper Chromatography Paper chromatography has been used to separate and detect pseudoephedrine hydrochloride from other pharmacologically active amines. Whatman No. 1 paper developed in n-butanol:water:95% acetic acid (4:5:1), n-butano1:toluene: water:95% acetic acid (10:10:5:5), ethyl acetate:water:95% acetic acid (3:3:1), o r chloroform:water:95% acetic acid (10:5:4) gave Rf values of 0.73, 0.35, 0.57, and 0.52 for pseudoephedrine hydrochloride respectively. Visualization of pseudoephedrine hydrochloride was done by spraying the chromatogram with 0.5% bromcresol green in methanol or 0.2% ninhydrin in acetic acid:butanol 5 :95.30 6.54 Gas Chromatography Pseudoephedrine hydrochloride has been separated from other arnines by gas chromatography. The oxazolidine

504

STEVEN A. BENEZRA AND JOHN

w.MCRAE

derivative has been prepared by the reaction of pseudoephedrine with anhydrous acetone. On a 1.15% SE-30, glass column, 2.4 m x 3 mm i.d. at 104OC the oxazolidine derivative has a retention time of 16.4 minutes.31

On a 15% PEG 6000, glass column 2 m x 4 mm i.d. at 175OC the oxazolidine derivative had a retention time of 10.1 minutes.32 The N-trifluroacetyl-L-prolylchloride derivative of pseudoephedrine has retention time of 105 minutes on a 3% SE-30, stainless steel column, 2 m x 3 mm i.d. at 170°C.33 An on-column acetic anhydride derivatization technique has been described for pseudoephedrine hydrochloride. Immediately after injection of a solution of pseudoephedrine onto a 20% SE-30, 1.8 m x 7 mm i.d. glass column at 125OC, an injection of acetic anhydride was made. The pseudoephedrine derivative formed on column has a retention time of 55.5 minutes as compared to a retention time of 8.7 minutes for underivatized pseudoephedrine.34 A variety of methods have been used to determine pseudoephedrine hydrochloride levels in plasma and urine by ~~ basefied gas chromatography. Bye and c o - w o r k e r ~extracted plasma or urine with diethyl ether. The ether extract concentrate was chromatographed on a 1.2 m x 2mm i.d. glass column packed with 2% Carbowax 20 M +5% KOH. The column was maintained at 187OC for plasma samples and 15OoC for urine samples. The heptafluorobutyric anhydride derivative of pseudoephedrine and electron capture detector have been used to enhance the sensitivity of the gas chromatographic method. Lin and c o - ~ o r k e r sand ~ ~ Cummins and Fourier37 extracted basefied urine or serum with benzene. Heptafluorobutyric anhydride is added to the benzene extract. The heptafluoroibutyric anhydride derivative extracted was chromatographed

505

PSEUDOEPHEDRINE HYDROCHLORIDE

on a 3% OV-17, 1.82 m x 2 mm i.d. glass column at 150°C36 or a 5% ethylene glycol succinate, 1.82 m x 2 mm i.d. stainless steel column at 140°C. 37 Pseudoephedrine in urine was analyzed by gas chromatography using a 2% polyethylene glycol 600 + 5% KOH,

2 m x 2 mm i.d. stainless steel column at 165OC. The urine was extracted with diethyl ether and then made basic with 5N NaOH. The pseudoephedrine was extracted with diethyl ether, concentrated, and injected directly into the gas chromatograph, or derivatized with acetone and then chromatographed.38 Pseudoephedrine was determined after acidification, precipitation, and acetic anhydride derivatization. The ester derivative was injected onto a 2.5% SE-30, 1.8 m x 4 mm i.d. column at 190°C.39 References 1.

N . F . XIV, Mack Printing Co., 1975

2. W. Martin, Burroughs Wellcome Co., personal communication 3 . R . Crouch, Burroughs Wellcome Co., personal communication 4.

J.W. McRae, unpublished data

5. D. Brent, Burroughs Wellcome Co., personal communication

6. B.S. Hurlbert, Burroughs Wellcome Co., personal communication 7. J. Ebron, Burroughs Wellcome, personal communication 8. M. Mathew, G.J. Palenik, Acta. Cryst., E, 1016 (1977)

9. V. Prelog, P. Haflinger, Helv. Chim. Acta., 33, 2021 (1950) 10. L.H. Welsh, J. h e r . Chem. SOC., 3500 (1949) 11. R. Seaman, Burroughs Wellcome Co., personal communication

c,

STEVEN A. BENEZRA AND JOHN W.MCRAE

506

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R.H. Manski, T.B. Johnson, J. h e r . Chem. SOC., 51,

1906

(1929) 13.

T. Morgan, Burroughs Wellcome Co., personal communication

14.

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15. 16. 17.

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187 (1973)

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K.L. Melmon, Clin. Res., 24, 252A (1976) R.G. Kuntzman, I. Tsai, L. Brand, L. Mark, Clin. Pharmacol. Ther., 12, 62 (1971) J. Bralet, Y. Cohen, G . Valette, Biochem. Pharm.,

11

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19. 20.

158, 135 (1967) J.E. Wallace, J. Pharm. S c i . , g ,1489 (1969) L. Chafetz, J. Pharm. Sci., 60, 291 (1971)

21.

J.A. McCrerie, Wellcome Foundation Ltd., personal communication

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3,766

(1974)

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