MATERIAL AND METHOD:

Pure sample of Esomeprazole was obtained from Wockhardt Ltd. Aurangabad and Levosulpiride from Wanbury Ltd. Mumbai as a gift sample. A UV/VIS Spectrophotometer (Chemito Spectrascan -2600) was used. Methanol AR (Merck Ltd. Mumbai) was procured from local market. The marketed formulation of Sompraz - L (40 mg ESO and 75 mg LSP) was procured from local market.

Selection of common solvent:

Methanol of analytical reagent grade was selected as common solvent for developing spectral characteristics of drug. The selection was made after assessing the solubility of both the drugs in different solvents.^[5]

Preparation of Standard Drug Solution:

Standard stock solutions containing Levosulpiride (LSP) and Esomeprazole (ESO) were prepared individually by dissolving 100 mg of LSP and of ESO separately in 50 ml of methanol AR. It was then sonicated for 10 minutes and the final volume of the solutions were made up to 100 ml with methanol to get stock solutions containing 1000 µg/mL each of LSP and ESO in two different volumetric flasks.^[4,5,6]

Determination of Absorption Maxima:

By appropriate dilution of two standard drug solutions with methanol AR, solutions containing 10 µg/ ml of each LSP and ESO were scanned separately in the range of 200- 500 nm to determine the wavelength of maximum absorption for both the drugs. LSP and ESO showed absorbance maxima at 234 nm (λ₁) and 300 nm (λ₂) respectively. The overlain spectra showed λ_max of both drugs and isosbestic points at 241 nm.^[4,5,6]

Method I (Simultaneous equation method):

Two wavelengths selected for the method are 234 nm and 300 nm that are absorption maximas of LSP and ESO respectively in methanol AR. The stock solutions of both the drugs were further diluted separately with methanol AR to get a series of standard solutions of 2-20 µg /mL of LSP and 1-10 µg/mL of ESO concentrations. The absorbance was measured at the selected wavelengths and absorptivities (A 1%, 1 cm) for both the drugs at respective wavelengths were determined as mean of three independent determinations. Concentrations in the sample were obtained by using following equations-^[2,6]

Where, A₁and A₂ = the absorbance’s of diluted solution at λ₁ and λ₂

a_{y1 and}a_y2 = absorptivity of Y at λ₁ and λ₂

a_{x1 and}a_x2= absorptivity of X at λ₁ and λ₂

Method II (Absorbance ratio or Q-analysis method):

From the overlain spectrum of LSP and ESO, two wavelengths were selected one at 241 nm, which is the isosbestic point for both the drugs and the other at 303 nm, which is λmax of ESO. The absorbances of the sample solutions prepared in a similar manner as in the previous method were measured and the absorptivity values for both drugs at the selected wavelengths were calculated. The method employs Q values and the concentrations of drugs in sample solution were determined by using the following formula:^[2,6]

For ESO

For LSP

A = Absorbance of sample at isosbestic point, a₁ and a₂ = Absorptivities of ESO and LSP respectively at Isosbestic point

Application of the proposed method for the determination of ESO and LSP in Capsules:

Twenty Capsules of the marketed formulation SOMPRAZ – L (SUN Pharmaceuticals, Mumbai) containing LSP 75 mg and ESO 40 mg were weighed, and finely powdered. For analysis of drug, quantity of powder equivalent to 18.75 mg of LSP and 10 mg of ESO was weighed and dissolved in 5 ml of methanol and sonicated for 10 minutes. Then the solution was filtered through Whatman filter paper no. 41 and the final volume of the solutions was made up to 10 ml with methanol to get a stock solution containing 1000µg/ ml of ESO and 2000 µg/ ml LSP. Appropriate aliquots of LSP and ESO within the Beer’s law limit were taken.

For Method I; the concentration of both LSP and ESO were determined by measuring the absorbance of the sample at 234 nm and 300 nm, values were substituted in the respective formula to obtain concentrations.

For Method II; the concentration of both LSP and ESO were determined by measuring absorbance of the sample at 241 nm and 300 nm and values were substituted in the respective formula to obtain concentrations. Results of capsule analysis are shown in Table 3.

Table 1: Linear regression analysis of calibration curves.

Parameter	Method I		Method II
Parameter	LSP	ESO	LSP	ESO
Beer’s law limit (µg/ml.)	2 – 20	1 – 10	2 – 20	1 – 10
Correlation coefficient (r)	0.9938	0.9974	0.9938	0.9974
Sandell's sensitivity (mcg/Sq.cm/0.001A)	0.2	0.001	0.2	0.001
Slope	0.038	0.042	0.038	0.042
Intercept	-0.008	0.017	-0.008	0.017

Table 2: Results of analysis of plain drug.

Analyte	Method I		Method II
Analyte	LSP	ESO	LSP	ESO
% Conc. Estimated (Mean ± S.D.)	99.2 ± 0.24	99.4 ± 0.20	99.3 ± 0.38	99.36 ± 0.34
Coefficient of variance	0.24	0.20	0.38	0.34

Table 3: Results of analysis of capsule samples.

Method	Drug	Label Claim (mg)	% Label Claim ± SD	Coefficient of variance
Method I	LSP	75	99.4 ± 0.173	0.17
Method I	ESO	40	98.7 ± 0.37	0.37
Method II	LSP	75	99.4 ± 0.24	0.24
Method II	ESO	40	100.2 ± 0.54	0.54

RESULT AND DISCUSSION:

Under described experimental conditions, the calibration curve and assay of capsule was performed. Using appropriate dilutions of standard stock solution, the two solutions were scanned separately. A critical evaluation of proposed methods were performed by statistical analysis of data where slope, intercept, correlation coefficient were studied. Beer’s law is obeyed in the concentration range of 1 – 10 µg/ml for ESO and 2 – 20 µg/ml of LSP and a correlation coefficient of 0.9974 and 0.9938 for both the drug ESO and LSP respectively. The proposed methods were also evaluated for commercially available capsule containing ESO and LSP in combination. The % assay from method I; was found to be 98.7 % for ESO and 99.4 % for LSP while from method II; 100.2 % for ESO and 99.4 % for LSP were found. The accuracy and reproducibility is evident from the generated data as result obtained are close to 100% and the standard deviation is low.

CONCLUSION:

The proposed method I and II provides simple, accurate, fast and reproducible quantitative analysis for simultaneous estimation if ESO and LSP in capsule. These methods can be successfully applied for the simultaneous estimation of ESO and LSP in capsule dosage form without prior separation and any interference in quality control.

ACKNOWLEDGEMENT:

The authors are grateful to Mr. Suresh M. Dhariwal, Hon, Secretary, JTES, Jamner for providing facilities to carry out this work in the research laboratory of SSJIPER. The authors are thankful to the Wockhardt Pharma. Aurangabad and Wanbury Pharma. Mumbai for providing gift samples of the drugs.

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Received on 14.07.2012 Accepted on 09.09.2012

Asian J. Pharm. Ana. 2(4): Oct. - Dec. 2012; Page 106-109