Spectrophotometric Method for Simultaneous Estimation of Olmesartan Medoxomil and Amlodipine Besylate in Pharmaceutical Preparations

 

SK Shah¹*, AJ Asnani¹, DP Kawade¹, SC Dangre²

¹J. L. Chaturvedi College of Pharmacy, Electronic Zone Building, MIDC, Hingna Road, Nagpur (M.S), India-440016

²Shrarad Pawar College of Pharmacy, Hingna road, Wanadongri, Nagpur-440016, Maharashtra, India.

*Corresponding Author E-mail: shah.sapan@rediffmail.com

ABSTRACT:

Simple spectrophotometric method has been developed for simultaneous estimation of Olmesartan Medoxomil and Amlodipine Besylate in combined dosage form. The method employed simultaneous equation method for analysis using methanol as a solvent. The two wavelengths 256 nm and 364 nm were selected for estimation of Olmesartan Medoxomil and Amlodipine Besylate respectively. Linearity was observed in the concentration range of 2-20 μg/mL for both the drugs Olmesartan Medoxomil and Amlodipine Besylate. The recovery studies ascertained the accuracy of the proposed method and the results were validated as per ICH guidelines. The method can be employed for estimation of pharmaceutical formulations with no interference from any other excipients and diluents.

 

 

INTRODUCTION:

Amlodipine,R,S-2-[(2-aminoethoxy)methyl]-4-(2-chlorophenyl)-ethoxycarbonyl-5-methoxy -car-bonyl-6-methyl-1,4-dihydropyridine (Figure 1) is potent calcium channel blocker.¹ Olmesartan medoxomil (5-methyl-2-oxo-1,3-dioxolen-4-yl)methoxy-4-(1-hydroxy-1-methylethyl)-2-propyl-1-{4-[2-(tetrazol-5-yl)-phenyl]phenyl}methyl imidazol-5-carboxylate) (Figure 2), is a potent and selective angiotensin AT1 receptor blocker.² Literature survey reveals the availability of several methods for estimation of amlodipine besylate (AMLO) includes UV^3-5, HPLC^6-8, HPTLC⁹ as alone or in combination with other drugs. No method has been reported for the estimation of AM and OLM in combined dosage form. Present work emphasizes on the quantitative estimation of AM and OLM in their combined dosage form by UV visible spectrophotometric method.

 

MATERIAL AND METHODS:

Instrument:

UV-visible double beam spectrophotometer, Shimadzu UV- 1601PC with matched pair quartz cells corresponding to 1 cm path length.

 

Chemicals:

All chemicals and reagents used were of analytical grade and purchased from Merck Chemicals, India.

 

Preparation of stock solution:

AM (Amlodipine besylate equivalent to 50 mg of amlodipine) and OLM (Olmesartan medoxomil equivalent to 50 mg of olmesartan) were accurately weighed and transferred to two separate 50 mL volumetric flasks, dissolved in methanol to obtain stock solution of concentration 1 mg/mL each.

 

Selection of λmax;

From these stock solutions, working standard solutions were prepared by appropriate dilution of aliquot portions with distilled water to get final concentration of 10 μg/mL for both AM and OLM. These solutions were scanned in the wavelength range of 200-400 nm to determine the λmax. AM shows λmax at 364 nm while OLM at 256 nm, respectively (Figure 1).

 

Preparation of standard solution:

From the standard stock solution 2 mL of AM and 8 mL of OLM was taken in 100 mL volumetric flask. Volume was made upto the mark with distilled water. The standard mixture solutions of 8 mg/mL and 2 mg/mL of (OLM and AM respectively) were analyzed to get the spectra, absorbance measured at 256 nm and 364 nm. A₁ and A₂ are absorbance of diluted sample at 256 nm and 364 nm respectively.

 

Figure 1: Overlain zero order spectrum of OLM (10 mg/mL) and AM (10 mg/mL)

 

Preparation sample solution:

Twenty tablets were weighed accurately and powdered.  Weigh the powder equivalent to 5 mg of AM and transferred to 100 mL volumetric flask and dissolved in methanol by shaking the flask for 10 minutes. The volume was made up to the mark using methanol. The solution was filtered through Whatman filter paper no. 41 and 1 mL of filtrate was further diluted to 25 mL with distilled water to obtain final concentration of  2 mg/mL of AM ( or 8 mg/mL of OLM). The absorbances of standard and sample solutions were measured at 256 and 364 nm using solvent blank. The results were calculated by the formula ¹⁰.

 

 

……….Eq. (2.1a)

 

……….Eq. (2.1b)

 

Where, A1 and A2 are absorbance of diluted mixture at 256 and 364 nm respectively, Cx and Cy are the concentration of AM and OLM respectively (g/100 mL), ax₁ and ax₂ are absorptivities of OLM at 256 and 364 nm respectively, ay₁ and ay₂ are absorptivities of AM at 256 and 364 nm respectively.

 

Validation of Method:¹⁰

The method was validated in terms of linearity, accuracy, precision and specificity of the sample applications. The linearity of the method was investigated by serially diluting the stock solutions of AM, OLM and measured the absorbance at 256 and 364 nm. Calibration curves were constructed by plotting the absorbance against the concentration. Both the drugs show linearity in the concentration range from 2-20 μg/mL with correlation coefficient of 0.999. Recovery studies were carried out to study the accuracy of the proposed method and ascertained by standard addition method. A known amount of drug was added to preanalysed tablet powder, at three levels and the percentage recoveries were calculated. Precision was found to be lower than 2 %. Ruggedness of the proposed method is determined by analysis of aliquots from homogenous slot by different analysts using similar operational and environmental conditions. Specificity study was performed by keeping the sample under various stressed conditions as at 60^oC and at 50^oC by adding 1 mL of 0.1N HCl, 0.1N NaOH, 3% H₂O₂ solutions.

 

RESULTS AND DISCUSSION:

Tablets were analyzed and amount of drug determined by proposed method was in good agreement with the labelled claim. The results of the marketed formulations were found to be 100.278±0.9232 and 100.608±0.4933 for OLM and AM respectively. The proposed method was validated as per the ICH guidelines. Linearity was determined at different concentration, AM and OLM both shows linearity in the concentration range of 2-20 μg/mL with correlation coefficient of 0.999. System reproducibility was determined by five replicate applications and five times measurement of a laboratory mixture at the analytical concentration. The reproducibility of sample was expressed in terms of S.D. and % R.S.D. There was no interference from the common excipients present in tablets. The recovery of drug was determined at 80, 100 and 120 % levels. The percent recovery was from 100.28 to 100.79 for OLM and 99.44 to 100.708 for AM indicating that method has required accuracy. Specificity studies results reveal that both the drugs degraded in presence of acid. Ruggedness was performed under three different conditions different days, different analysts and intraday. The results show the % RSD values < 2 % signifies the precision of the method.

 

 

Table 1. Results of marketed formulation, recovery and intermediate precision

Drugs	Parameters	% Labeled claim	% Recovery*			Intermediate Precision*
			80	100	120	Interday	Intraday	Different analyst
OLM	Mean	100.278	100.79	100.281	100.29	100.34	100.033	100.157
	± S.D.	±0.9232	0.625	0.391	0.036	± 0.2260	± 0.2702	± 1.27
	% RSD	0.9206	0.6208	0.389	0.0359	0.225	0.27	1.19
AM	Mean	100.608	99.44	100.708	99.876	99.6467	100.963	100.52
	± S.D.	± 0.4933	0.265	0.381	0.708	± 0.8949	± 0.9943	± 0.5139
	% RSD	0.4903	0.266	0.378	0.709	0.898	0.984	0.511

 

 

The proposed method for simultaneous estimation of OLM and AM in combined dosage form was found to be simple, accurate, precise, sensitive, and economical. It can be employed for estimation of pharmaceutical formulations in quality control departments.

 

ACKNOWLEDGEMENTS:

The authors are thankful to Dr. D. R. Chaple, Principal,      J. L. Chaturvedi College of Pharmacy, Nagpur for providing laboratory facilities. The authors also wish cordial thanks to Mr. Anwar Daud, Managing Director, Zim Laboratories Ltd., Nagpur for providing facilities and environment conducive for an ideal research to flourish.

 

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Accepted on 04.07.2012      © RJPT All right reserved