A simple bioanalytical assay for determination of montelukast in human plasma: Application to a pharmacokinetic study

Journal of Chromatography B, 869 (2008) 38–44

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Journal of Chromatography B journal homepage: www.elsevier.com/locate/chromb

A simple bioanalytical assay for determination of montelukast in human plasma: Application to a pharmacokinetic study Pattana Sripalakit a,b,∗ , Bungon Kongthong c , Aurasorn Saraphanchotiwitthaya d a

Department of Pharmaceutical Chemistry and Pharmacognosy, Faculty of Pharmaceutical Sciences, Naresuan University, Phitsanulok 65000, Thailand Bioequivalent Test Center, Faculty of Pharmaceutical Sciences, Naresuan University, Phitsanulok 65000, Thailand c SGS (Thailand) Ltd., Bangkok 10120, Thailand d Department of Pharmaceutical Technology, Faculty of Pharmaceutical Sciences, Naresuan University, Phitsanulok 65000, Thailand b

a r t i c l e

i n f o

Article history: Received 14 February 2008 Accepted 6 May 2008 Available online 16 May 2008 Keywords: Montelukast Assay HPLC Validation Pharmacokinetics

a b s t r a c t An analytical method based on high-performance liquid chromatographic (HPLC) was developed for the determination of montelukast in human plasma using mefenamic acid as an internal standard. After precipitation of plasma proteins with acetonitrile, chromatographic separation was carried out using a Zorbax Eclipse® XDB C8 (150 mm × 4.6 mm i.d., 5 ␮m) with mobile phase consisted of methanol–acetonitrile–0.04 M disodium hydrogen orthophosphate (22:22:56, v/v, pH 4.9). The wavelengths of fluorescence detection were set at 350 nm for excitation and 450 nm for emission. The linearity was confirmed in the concentration range of 5–1000 ng/ml in human plasma. Intra- and inter-day accuracy determined from quality control samples were 101.50 and 107.24%, and 97.15 and 100.37%, respectively. Intra- and inter-day precision measured as coefficient of variation were ≤4.72 and ≤9.00%, respectively. Extraction recoveries of drug from plasma were >48.14%. The protocol herein described was employed in a pharmacokinetic study of tablet formulation of montelukast in healthy Thai male volunteers. © 2008 Elsevier B.V. All rights reserved.

1. Introduction Montelukast sodium (2-[1-[1(R)-[3-[2(E)-(7-chloroquinolin2-yl)vinyl]phenyl]-3-[2-(1-hydroxy-1-methylethyl)phenyl] propylsulfanylmethyl]cyclopropyl] acetic acid mono-sodium salt; Fig. 1), is a potent and specific cysteinyl leukotriene D4 (LTD4 ) receptor antagonist [1,2]. It is currently being used for the prophylaxis and treatment of chronic asthma [3–7]. Various analytical methods have been developed to determine montelukast in dosage formulations [8–10] and human plasma samples, such as voltammetry [10] and chromatographic assays [11–16]. The use of columnswitching [12,13], dual-column [16], and microtiter plate [15] has also been incorporated with the process of high-performance liquid chromatographic (HPLC) analysis. Some methods do not use internal standards [13,16] whereas others use synthetic derivatives [11,12,15] or quinine bisulfate [14] as internal standards. The analysis of montelukast published by Al-Rawithi et al. [14] seems to be the method of choice for the preliminary study, but sometimes the internal standard, quinine bisulfate was co-eluted with

∗ Corresponding author at: Department of Pharmaceutical Chemistry and Pharmacognosy, Faculty of Pharmaceutical Sciences, Naresuan University, Phitsanulok 65000, Thailand. Tel.: +66 55 261000x1861; fax: +66 55 261057. E-mail address: [email protected] (P. Sripalakit). 1570-0232/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jchromb.2008.05.017

the interference peaks. Montelukast is a light-sensitive compound and the photo-isomerization can occur when it is exposed with UV irradiation [13,14]. Therefore, sample handling is necessary prior to analysis. The lower limit of quantification between 1 and 30 ng/ml using 100–300 ␮l human plasma volumes [11–16] has been described and the preparations of sample were performed by plasma protein precipitation in all of these studies [11,12,14–16]. In the present study, a sensitive and accurate alternative HPLC method for the determination of montelukast in human plasma based on the commercially available internal standard (mefenamic acid; Fig. 1) and a simple HPLC column system has been validated. The analytical method established was to be applied to samples obtained from a pharmacokinetic study in healthy volunteers who received oral dose of montelukast. 2. Experimental 2.1. Chemicals and reagents Montelukast sodium (98.6%) and mefenamic acid (99.55%), an internal standard were purchased from SynFine Research, Inc. (Ontario, Canada) and Zhejiang Tianxin Pharmaceutical, Co., Ltd. (Zhejiang, China), respectively. Sodium acetate trihydrate used was of analytical reagent grade purchased from Merck (Darmstadt, Germany). Methanol and acetonitrile were of HPLC grade

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2.4. Sample preparation All plasma samples were thawed at room temperature. To 500 ␮l thawed plasma were added 500 ␮l internal standard solution and 500 ␮l acetonitrile in a screw-cap glass tube. The mixture was vortex-mixed for 60 s and centrifuged at 4000 rpm for 10 min at 4 ◦ C. The supernatant was transferred to an autosampler vial and 50 ␮l was injected into the HPLC system. 2.5. Validation of analytical method 2.5.1. Selectivity Six lower limit QC samples were prepared from 6 different matrix sources. Selectivity was determined by comparing the interfering peaks between these QC samples and their blank plasma. 2.5.2. Linearity and choice of the weighting factor The eight-point calibration curve was constructed by plotting the peak response (area or height) ratio of montelukast to Fig. 1. Chemical structures of montelukast and mefenamic acid.

and glacial acetic acid was of analytical grade obtained from Carlo Erba (Barcelona, Spain). High purity water was supplied by Milli-Q Water Purification System (Millipore, Billerica, MA). Human plasma was supplied by Thai Red Cross Society (TRCS, Bangkok, Thailand). 2.2. Chromatographic conditions The HPLC system (Agilent Technologies, Inc., Santa Clara, CA) consisted of a vacuum degasser (G1322A), a quaternary pump (G1311A), a spectrofluorometric detector (G1321A) equipped with an autosample injector (G1313A) fitted with a 50-␮l sample loop. The analytical column employed was Zorbax Eclipse® XDB C8 (150 mm × 4.6 mm i.d., 5 ␮m particle size) purchased from Agilent Technologies, Inc. The mobile phase was comprised of acetonitrle–25 mM acetate buffer pH 4.0 containing sodium acetate trihydrate (3.4 g/l) adjusted to pH 4.0 ± 0.1 with glacial acetic acid (70:30, v/v). The mobile phase was prepared weekly and was filtered before use. All separations were performed isocratically at a flow rate of 1.0 ml/min and column condition was maintained at ambient temperature. The detector was operated at an excitation wavelength of 350 nm and an emission wavelength of 450 nm. 2.3. Calibration standards and quality controls Due to the light sensitivity of montelukast, stock solutions, calibration standards, quality control samples and unknown samples were kept in amber glass containers or protected from light by wrapping the tube in aluminum foil. The stock solution of montelukast and mefenamic acid (1 mg/ml) were separately prepared in acetonitrile–methanol (70:30, v/v) and methanol, respectively. All eight-point calibration curves of with concentrations of 5, 10, 20, 50, 100, 200, 500 and 1000 ng/ml were prepared by dilution of aliquots of the stock solution with human plasma. Three quality control (QC) solutions containing low (15 ng/ml; LQC), medium (75 ng/ml; MQC) and high (750 ng/ml; HQC) including lower limit (5 ng/ml; LLQC) and upper limit (1000 ng/ml; ULQC) were prepared in a similar way. A working internal standard solution was prepared in acetonitrile to yield the concentration of 100 ng/ml. All stock solutions were stored at 4 ◦ C and all prepared plasma samples were stored at −40 ◦ C until analysis.

Fig. 2. Representative chromatograms of: (A) blank (drug-free) plasma, (B) plasma spiked with 5 ng/ml montelukast and 100 ng/ml mefenamic acid (LLQC) and (C) plasma spiked with 1000 ng/ml montelukast and 100 ng/ml mefenamic acid (ULQC).

[16] None C18 (Dual-column)

No

No

No

Yes

HPLC-Fl (350/400 nm)

HPLC-Fl (350/400 nm)

HPLC-Fl (350/400 nm)

HPLC-Fl (350/440 nm)

Protein precipitation (100 ␮l)

C18

C18 (Columnswitching) C8 Direct injection (300 ␮l)

Yes HPLC-Fl (350/400 nm)

Protein precipitation (150 ␮l) Protein precipitation (300 ␮l)

Chiral (Columnswitching) Protein precipitation (300 ␮l)

C18 Protein precipitation (200 ␮l)

HPLC-Fl, HPLC coupled with fluorescence detection; LOQ, limit of quantification; L-705,254, synthetic derivative of montelukast.

1 (5–2000)

[15] L-705,254 3 (–1000)

[14] Quinine bisulfate 20 (20–2000)

[13] None 1 (1–500)

[12] L-705,254 28.9 (28.9–386)

[11] L-705,254 30 (30–3000)

Mefenamic acid 15 (15–1000)

No

Extraction method (plasma volume)

HPLC-Fl (350/400 nm)

The method demonstrated excellent chromatographic specificity with no endogenous plasma interference at the retention times of montelukast and the internal standard. Representative chromatograms for blank plasma and plasma spiked with motelukast and the internal standard are shown in Fig. 2. Mefenamic acid and montelukast were well resolved with good symmetry with respective retention times of 3.4 and 7.7 min and an analytical run time of less than 10 min. The published HPLC methods for determination of montelukast in human plasma were

No

3.1. Development of HPLC method

HPLC-Fl (350/400 nm)

3. Results and discussion

Analysis with isomer

The method was applied to evaluate the pharmacokinetic of montelukast in 48 healthy Thai male volunteers. Each volunteer was orally administered 10 mg montelukast (Singulair® ; Merck Sharp & Dohme Ltd., Northumberland, England) under fasting conditions. Blood samples were collected in heparinized tubes before 0.5 h dosing and at 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 6, 8, 12, 16 and 24 h post-dosing and centrifuged to obtain the plasma fraction. The plasma samples were kept in cryogenic vial stored at −40 ◦ C until analysis. The pharmacokinetic parameters for each volunteer were evaluated from the plasma concentration–time profile calculated by WinNonlin Professional version 5.0.1 (Pharsight Corporation, Mountain View, CA, USA) with non-compartment analysis. This study was approved by the Naresuan University Ethical Committee before obtaining informed written consent from all volunteers.

Table 1 Comparison of published HPLC methods for the determination of montelukast in human plasma

2.6. Pharmacokinetic study

Stationary phase

Mobile phase (v/v)

2.5.5. Stability To test the freeze-thaw stabilities of extracted montelukast, low and high QC samples were analyzed after three freeze-thaw cycles by freezing for 24 h and then thawing at room temperature. The short- and long-term stabilities were also determined during storage for 12 h at room temperature and 9 weeks at −20 ◦ C, respectively. Post-preparative stabilities were studied over a 20-h storage period at room temperature in the autosampler tray. Stabilities of stock solutions of montelukast and mefenamic acid were studied at the applied concentrations over a period of 6 h at room temperature and 7 days at 4 ◦ C month. Subsequently, these results were compared with those obtained form freshly prepared samples.

Acetonitrile: 25 mM acetate buffer pH 4.0 (70:30) Acetonitrile: 0.05 M ammonium phosphate pH 3.5 (62:38) (A) Acetonitrile and methanol: ammonium acetate (pH 3.6, 10 mM) (10:100) (B) Acetonitrile: ammonium acetate (pH 5.8, 10 mM) (32.5:100) Acetonitrile: 25 mM acetate buffer (80:20) 0.025 M Sodium acetate pH 4.0: acetonitrile (20:80) Acetonitrile: 0.02 M ammonium phosphate pH 3.5 (65:35) Acetonitrile: water: glacial acetic acid (75:25:0.25)

2.5.4. Recovery The efficiency of montelukast extraction from human plasma was measured analyzing three levels of QC samples. The drug recovery was determined by comparing peak heights obtained from the spiked QC plasma samples after extraction and reconstitution to the standard solution at the same concentration of the spiked QC plasma samples.

C8

LOQ (range) (ng/ml)

2.5.3. Accuracy and precision Five different concentrations including lower and upper limits of QC samples (5, 15, 75, 750 and 1000 ng/ml) in six replicates were analyzed in 5 different days in order to determine the intra- and inter-day accuracy and precision.

Protein precipitation (500 ␮l)

Internal standard

Reference

mefenamic acid (y) versus concentration of montelukast in plasma (x) on six separate batches. The linearity was analyzed using weighted least-square linear regression since heteroscedasticity of the data was observed. Different weighting factors (wi ) were evaluated and the selection of the best one was based on the  calculation of the respective sum of the absolute relative errors ( |% RE|) over the whole concentration range for each weighting factor [17].

Presented report

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Method

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Fig. 3. Percentage relative error versus concentration obtained form various weighting factors calculated from peak area ratio: wi = 1 (A), wi = 1/x (B), wi = 1/x2 (C) and peak height ratio: wi = 1 (D), wi = 1/x (E), and wi = 1/x2 (F).

summarized and compared to the presented report in Table 1. On the basis of our results, the total run time was less than that reported by Liu et al. [12] and Ochiai et al. [13] using columnswitching technique. Furthermore, this simple method did not require the synthetic internal standards [11,12,15], which is not available commercially. 3.2. Linearity, calibration curves and sensitivity The suitability of least-square linear regression was proved by applying the F-test that performs in order to check the homoand heteroscedasticity, and plotting residuals versus concentration obtained for data of six separate batches. The result indicated that the experimental F-value was higher than the tabled F-value and the residual plot clearly showed that error was not randomly distributed around the concentration axis (data not shown). Thus, heteroscedasticity of the data was evident and the weighted leastsquare linear regression was used to fit the data. The percentage relative error (% RE) plots unweighted and weighted regressions of the montelukast assay data across the whole concentration range are shown in Fig. 3. The regression parameters of the calibration  curve generated for each weighting factor and the respective |%

RE| are summarized in Table 2. The weighting factor 1/x2 calculated from peak height ratio presented not only the best % RE distribution scatter  at the lower end of 2the calibration curve, but also the smallest |% RE|. Thus, the 1/x weighting factor calculated from peak height was chosen. The calibration curve for montelukast was linear from 5 to 1000 ng/ml with a regression coefficient of >0.99. Based on

Table 2 Regression parameters of the calibration curve generated for each weighting factor and the respective sum of the absolute percentage relative errors r2

a



|% RE|

y

wi

b

Peak area ratio

1 1/x 1/x2

0.00496 0.00500 0.00492

0.01671 0.00759 0.00938

0.99935 0.99936 0.99824

486.52 315.30 316.40

Peak height ratio

1 1/x 1/x2

0.00422 0.00421 0.00407

−0.00336 −0.00033 0.00257

0.99951 0.99920 0.99749

385.85 302.21 281.30

y = peak ratio (dependent variable); x = concentration of montelukast (independent variable); wi = weighting factor; b = slope of the regression equation; a = y-intercept of the regression equation; r2 = regression coefficient; % RE = [(Cfound − Cnom )/Cnom ] × 100, when % RE = percentage relative error; Cfound = the regressed concentration; Cnom = the nominal standard concentration.

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Table 3 Intra-day and inter-day assay accuracy and precision for montelukast in human plasma Nominal concentration (ng/ml)

Observed concentration (mean ± S.D.; ng/ml)

Intra-day (n = 6) 5.11 (LLQC) 15.33 (LQC) 76.65 (MQC) 766.48 (HQC) 1021.97 (ULQC)

5.48 15.56 79.76 814.29 1095.29

± ± ± ± ±

Inter-day (n = 5) 5.11 (LLQC) 15.33 (LQC) 76.65 (MQC) 766.48 (HQC) 1021.97 (ULQC)

4.96 15.10 76.93 768.53 1024.97

± ± ± ± ±

Accuracy (% accuracy)

Precision (% CV)

0.26 0.71 2.49 37.86 27.50

107.24 101.50 104.06 106.23 107.17

4.72 4.56 4.56 4.65 2.51

0.45 0.68 3.55 56.34 86.55

97.15 98.48 100.37 100.27 100.29

9.00 4.48 4.61 7.33 8.44

LLQC, lower limit quality control; LQC, low quality control; MQC, medium quality control; HQC, high quality control; ULQC, upper limit quality control.

Table 4 Absolute recovery of the method for determining the concentration of montelukast in human plasma Nominal concentration (ng/ml)

Absolute recovery (mean ± S.D.; %)

% CV

Montelukast (n = 6) 15.33 (LQC) 76.65 (MQC) 766.48 (HQC)

53.21 ± 1.32 57.18 ± 4.25 48.14 ± 1.85

2.48 7.44 3.84

Mefenamic acid (n = 6) 100.00

98.97 ± 1.60

1.62

500-␮l plasma sample the LOQ, defined as the lowest quantifiable concentration on the calibration curve which both accuracy and precision should be within the maximum tolerable CV of 20%, was deemed to be 5 ng/ml. This sensitivity was better than the report of Al-Rawithi et al. [14] based on the methods using of commercially available internal standard. 3.3. Accuracy, precision and recovery The intra- and inter-day accuracy and precision results of montelukast in human plasma were summarized in Table 3. The intra-day precision, expressed as CV for five QC samples including LOQ was 2.51–4.72% and the inter-day CV for the same QC samples was 4.48–9.00%. The mean extraction recoveries determined at LQC, MQC and HQC are shown in Table 4. The overall average recovery was 52.84% with a CV between 2.48 to 7.44% determined from three different concentrations. The overall average recovery of montelukast in presented study was difference from that of Al-Rawithi et al. [14] (>95%) using the same method of protein precipitation, since montelukast is more than 99% bound to plasma proteins [7]. The difference ratio and type of mixtures (e.g. ace-

tonitrile, solvent of internal standard and others) that added to the plasma sample to extract the analyte, may mainly effect on the recovery. A recovery of 98.97% was obtained for the internal standard. These results indicate that the method was reliable and reproducible within the acceptance ranges [18]. 3.4. Stability The stability tests of two QC samples were designed to cover anticipated conditions that clinical samples may experience. Stability data were summarized in Table 5. Briefly, three freeze-thaw cycles and ambient temperature storage of the freezed quality control samples up to 12 h prior to sample preparation appeared to have no effect on the quantification of analyte. Quality control samples stored in a freezer at −20 ◦ C remained stable for at least 9 weeks. For bench-top stability, there was no observed effect on quantification for the extracted samples kept in room temperature for 20 h. The stock solutions of both drug and the internal standard were stable in room temperature at least 6 h and in 4 ◦ C for 7 days. Indeed, some acyl-glucuronide or sulfoxide conjugated metabolites of montelukast have been found in human [19]. The stability of montelukast in plasma from the volunteers kept at −20 ◦ C after a few months was re-analyzed. The results show that no significant difference between the original and repeated analyses. 3.5. Pharmacokinetic study This method has been successfully used to pharmacokinetic study of montelukast after a single oral dosing of 10-mg tablet formulation for 48 healthy Thai male volunteers. The representative chromatograms from the pre- and post-dose samples are provided in Fig. 4. The mean plasma concentration profiles are shown in Fig. 5.

Table 5 Stability of montelukast in human plasma QC concentration (ng/ml)

Initial concentration (mean ± S.D.; ng/ml)

Measured concentration (mean ± S.D.; ng/ml)

Deviation (%)

Freeze-thaw stability (three freeze-thaw cycles) (n = 3) 15 (LQC) 15.41 ± 0.27 750 (HQC) 749.65 ± 26.97

15.51 ± 0.59 810.31 ± 13.85

+0.65 +8.09

Long-term stability (9 weeks at −20 ◦ C) (n = 3) 15 (LQC) 15.09 ± 0.42 750 (HQC) 748.94 ± 5.48

16.64 ± 1.18 776.11 ± 12.78

+10.27 +3.63

Short-term stability (12 h at room temperature) (n = 3) 15 (LQC) 14.82 ± 0.89 750 (HQC) 754.75 ± 25.78

14.72 ± 0.57 711.48 ± 26.51

−0.67 −5.73

Post-preparative stability (20 h at room temperature) (n = 3) 15 (LQC) 15.68 ± 1.03 750 (HQC) 820.76 ± 8.62

15.64 ± 0.83 824.95 ± 16.91

−0.26 +0.51

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Table 6 Calculated pharmacokinetic parameters of montelukast for healthy Thai male volunteers (n = 48) Pharmacokinetic parameters

Mean ± S.D.

Cmax (ng/ml) Tmax (h) AUC0−t (ng h/ml) AUC0−∞ (ng h/ml) T1/2 (h)

535.73 3.61 3712.41 3805.00 3.86

± ± ± ± ±

156.81 1.25 1020.29 1054.92 0.58

Cmax is the maximal concentration; Tmax is the time when the maximal concentration is reached; AUC0−t is the area under the curve from pre-dose to the last sampling time; AUC0−∞ is the are under the curve from pre-dose extrapolated to infinity; T1/2 is the elimination half-life.

The results of pharmacokinetic study of montelukast are presented in Table 6. The means of these parameters (Cmax , AUC0−t , AUC0−∞ , Tmax and T1/2 ) were within the ranges of values obtained from the previously report for the same dosing regimen in healthy young adults [7], whereas both Cmax and AUC0−t were 1.2–1.4 and 1.4–1.5 times, respectively, higher than those of the results of Cheng et al. [20] and Graff et al. [21] analyzed by HPLC method with fluorescence detector. 4. Conclusion A simple, accurate and reliable HPLC method for the quantitation of montelukast in human plasma has been developed and validated. The described method uses a fast and easy sample preparation, a commercially available internal standard and a simple HPLC system coupled with fluorescence detection. The use of the most appropriate weighting factor significantly improved the accuracy of the analytical method. The sensitivity of the assay is adequate for application in the study of clinical pharmacokinetic or bioequivalence test of montelukast formulation in human. Acknowledgements The authors wish to thank to Bioequivalence Test Center, Faculty of Pharmaceutical Sciences, Naresuan University (Phitsanulok, Thailand) by financial support and to all staff of the Bioequivalence Test Center. Fig. 4. Representative HPLC chromatograms of plasma taken from a healthy Thai male volunteer at: (A) 0 h (
Fig. 5. Mean plasma concentration–time curve after administration of 10-mg montelukast (Singulair® ) in healthy Thai male volunteers (n = 48).

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