Evaluation of astemizole purity by HPLC

Talanro, Vol. 40, No. 9, pp. 135i’-1360, 1993 Printed in Great Britain. All rights reserved

EVALUATION

Copyright0

0039-9140/93 $6.00 + 0.00 1993 Pergamon press Ltd

OF ASTEMIZOLE PURITY BY HPLC

M. V. SURYANARAYANA,*S.VENKATARAMAN,M.SAT~ANARAYANAREDDYand B. PARTHASARADHIREDDY Dr. Reddy’s Laboratories Ltd., Research and Development Division, 7-l-27, Amecrpet, Hyderabad 500 016, India

c. s. P. SASTRY School of Chemistry, Andhra University, Visakhapatnam

530 003, India

G. L. DAVIDKRUPADANAM Department of Chemistry, Osmania University, Hyderabad 500 007, India (Received 24 December 1992. Revised 16 March 1993. Accepted 22 March 1993)

Sunmuy-A liquid chromatographic method is described for the evaluation of Astemizole purity. The method is also applicable for the analysis of pharmaceutical dosage forms of Astemizole using indole as internal standard. Saparation was achieved with a p bondapak C,, column and phosphate buffer @H 6.0):acetonitrile (50:50 v/v) as eluent, at a flow rate of 1.5 ml/min with UV detection at 280 nm. The method is suitable for estimating the possible impurities if any present in Astemizoleup to 0.05%for la and 0.25% for lb. The method is simple, rapid and accurate for the analysis of Astemizole.

Astemizole [ 1-[(4-fluoro phenyl)methyl]-N[I-[Z(Cmethoxy phenyl)ethyl]-4-piperidinylllH-benzimidazol-2-amine; 1, Fig. l] is a new antihistamine of current interest that differs structurally from other antihistamines. Astemizole was found to be a long-acting non-sedating antihistamine with major clinical implications for the treatment of allergic diseases. Currently Astemizole and its pharmaceutical dosage forms are not found in any pharmacopoeia. However an analytical profile’ was found in a survey of the literature which include elemental analysis, radioimmunoassays and HPLC. The synthetic route to Astemizole was described in two patent&’ where in both 2-chloro1-[(4-fluoro-phenyl)methyl]- 1H benzimidazole (la, Fig. 1) and I-(2-(4-methoxy phenyl)ethyl)4-aminopiperidine (1b, Fig. 1) were allowed to react to give the expected product (1). Our investigation examined the product for the presence of both reactants as potential impurities. As the quantitative analysis’ of Astemizole was already published, our aim was to develop an HPLC procedure suitable for detecting these impurities in Astemizole and to apply the

*Author for correspondence.

same procedure for the analysis of this drug at various stages in the production of Astemizole. Also we want to apply these parameters for the assay of pharmaceutical dosage forms of Astemizole. A study of several combinations of different solvents and buffer systems, different types of stationary phases and suitable internal standards for proper quantification, led to the described analytical conditions giving sharp and well resolved peaks. EXPERIMENTAL Apparatus The HPLC (Waters Associates) instrument was equipped with a model 501 pump, U6K injector, model 481 variable wavelength UV detector. Separations were performed on a p bondapak Cls, 10 microns stainless steel column (Waters USA) 300 x 3.9 mm at ambient temperature. The flow rate of the system was maintained at 1.5 ml/min with UV detection at 280 nm. The attenuation was set at 2.0 AUFS (Absorbance units full scale) with a chart speed of 0.25 cm/min. Chromatographic peaks were electronically integrated and recorded with a model 745 (Waters Associates) computing integrator.

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M.V.

SURYANARAYANA

et al.

Reagents

Mixed indole and astemizole standard solution

Chromatographic grade acetonitrile, analytical reagent grade Potassium dihydrogen orthophosphate, dipotassium hydrogen orthophosphate, perchloric acid, and indole and Milli Q water were used throughout these experiments.

Four millilitres of Astemizole solution and 1.0 ml of Indole solution were transferred to a lo-ml standard flask and diluted to the mark with mobile phase. Sample preparation

A mass of powdered tablets equivalent to 25 mg of Astemizole was suspended in 25 ml of mobile phase and vortexed for 10 min. The insoluble portion, if any, was removed by filtration and the filtrate analysed after 4.0 ml of this solution was added to 1.0 ml of Indole standard.

Mobile phase

The mobile phase was composed of 50 : 50 v/v phosphate buffer pH 6.0 and acetonitrile. Buffer solution was prepared by mixing the solutions of 0.022M potassium dihydrogen orthophosphate and 0.003M dipotassium hydrogen orthophosphate, and the pH of the solution adjusted to 6.0 with O.OlM perchloric acid.

Procedure

Five microlitres of the mixed standard or sample were injected into a universal injector using a lo-p1 Hamilton Syringe. Each injection was done at an interval of 15 min to ensure complete elution of the previously injected material. Sample and mixed standard solutions were injected in triplicate. Quantitative determinations were made by comparison of the peak area ratio of Astemizole and Indole (Internal standard) for a sample injection to the

Indole standard solution

A OS-mg/ml mobile phase solution of Indole was used as the internal standard. Astemizole standard solution

A 1.O-mg/ml mobile phase solution of Astemizole was used as the drug standard.

[ASTEMIZ~LE

0 au “; 1

H2C

Cl

F

*

[2-CHLORO-l-[(4-FLlJ0f?0PHENY~METHYL]-lH

[l-(2-(G-METHOXY

, 1-J

PHENYL)

BENZIMIDAZOLE,

ETHYL)-4-AMINOPIPERIDINE,lbl

Fig. 1.

la]

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Evaluation of Astemiaole purity by HPLC

k.““”

0 2 4 6 8 10 12 14 TIME(min)

Fig. 3. Separation of indole and astemizole (1) by HPLC on p bondapak C,, column.

0 2 4 6 8 10 12 14 TIME(min)

Fig. 2. HPLC separation of astemizole (I), l(a) and l(b).

corresponding area ratio for a mixed standard injection. Blank samples showed no interfering peaks. Impurity

analysis of Astemizole

To demonstrate HPLC resolution of Astemizole, l(a), and l(b), mobile phase solutions were prepared by adding known amounts of l(a) and l(b), 0.05 to l.O%, to Astemizole. The impurity levels were also determined by comparison of peak area ratios for solutions of l(a) and l(b) at the levels up to 0.05 and 0.25%, respectively. RESULTS AND DISCUSSION

The systematic study of the operating parameters that would optimize the HPLC resolution of chemical compounds involved in the synthesis of Astemizole led to the procedure. As shown in Fig. 3, Astemizole and Indole (Internal standard) are distinctly eluted having retention times of 10.76 and 4.88 min, respectively. The ratios of peak area of Astemizole to that of Indole (Internal standard) were plotted against concentrations of Astemizole. The plot

was linear over the range 0.125-3.0 pg with a standard deviation of 0.137. As shown in Fig. 2, Astemizole, l(a) and l(b) were distinctly eluted having retention times of 10.76, 7.80 or 2.78 min, respectively, with detection limits of 0.05% for l(a) and 0.25% for l(b). Tablets of Astemizole were analysed by the proposed and reference HPLC methods and the results are tabulated in Table 1. The accuracy of the method was further ascertained through recovery studies by adding known amounts of Astemizole to placebo tablet powder and analysed by HPLC. Recovery was found to be 99.499.8%. These values indicate a lack of interference by the tablet diluents and lubricants. The precision of the method was found to

Table 1. Assay of Astemizole in pharmaceutical dosage forms by the proposed method % Label claim Sample No.

I 2 3 4 5

Sample Tablet Tablet Tablet Tablet Tablet

Content (w) 10 10 10 10 10

Proposed HPLC method

Reference method*

99.4 99.8 99.6 99.8 99.6

:; 99:5 99.8 99.6

lHPLC method reported for pharmaceutical dosage forms in the analytical profile of Astemiaole.

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M. V. SURYANARAYANA et al.

be 99.4-99.7% with a standard deviation of 0.04, giving evidence of excellent precision. In conclusion, the proposed HPLC method allows rapid separation and determination of starting materials l(a) and l(b), which may be present in crude Astemizole. The method is also useful for the determination of Asteniizole and its pharmaceutical dosage forms and results are comparable with the reported HPLC method.’ Acknowledgemenr-The

authors are grateful to Dr. B. Saida

Reddy of Dr Reddy’s group for providing samples of Astemizole and its intermediates. REFERENCES 1. Abdulrahman M. Al-Obaid and Mohammad Saleem Main, in Analytical Profires of Drug Substances, Klaus Florey (ed.), Vol. 20, p. 173. Academic Press, New York, 1991. 2. Laboratorio Fides S.A. Span. ES 533, 613 (Cl. C07D235/30), 16 Jun 1985, Appl 22 Jun 1984, 7pp. 3. Montserrat Faba, Eusebio (Inke S.A.) Span. ES 542, 807 (Cl. CO7D401/12), 16 Dec. 1985, Appl. 03 May 1985.