Simultaneous Spectrophotometric Determination of Lansoprazole and Domperidone in Capsule Dosage Form

.: Simultaneous Estimation of Lansoprazole and Domperidone in Capsules Two simple, accurate and precise spectrophotometric methods have been developed for simultaneous determination of lansoprazole and domperidone in pharmaceutical dosage form. Method A involves formation of Q-absorbance equation at 256.0 nm (isoabsorptive point) and at 294.2 nm while method B is two wavelength method where 277.6 nm, 302.1 nm were selected as λ 1 and λ 2 for determination of lansoprazole and 231.3 nm, 292.0 nm were selected as λ 1 and λ 2 for determination of domperidone. Both the methods were validated statistically and recovery studies were carried out. The Beer’s law limits for each drug individually and in mixture was within the concentration range of 5-50 µg/ml. Linearity of lansoprazole and domperidone were in the range of 24-36 µg/ml and 8-12 µg/ml, respectively. The proposed methods have been applied successfully to the analysis of the cited drugs either in pure form or in pharmaceutical formulations with good accuracy and precision. The method herein described can be employed for quality control and routine analysis of drugs in pharmaceutical formulations.

Reference standard of LAN was obtained from Dr. Reddy's Laboratories Ltd., Medak, India and DOM was obtained from Aurobindo Pharma Ltd., Hyderabad, India. All the reagents and chemicals were either of AR grade or spectroscopy grade. All the solutions were freshly prepared with double distilled water. Spectral absorbance measurements were made with Shimadzu UV-2401 double beam spectrophotometer with 1 cm matched quartz cell.
About 60 mg of LAN and 20 mg DOM were separately taken in a 100 ml volumetric flask, dissolved in a mixture of methanol and 0.1 M NaOH (70:30 v/v) and volume was made up to the mark. The standard stock solutions were further diluted separately to obtain a concentration of 30 μg/ml of LAN and 10 μg/ml of DOM. The resulting solutions were scanned in the range of 200-400 nm. The UV absorption overlain zero order spectrum for LAN and DOM is depicted in fig. 1. From the overlain spectra, the wavelengths 256.0 nm (isoabsorptive point) and 294.2 nm (λmax of LAN) were selected for formation of Q-absorbance equation. The standard stock solutions of these drugs were diluted to obtain a concentration range of 10-100 μg/ml and absorbances were measured at selected wavelengths. The concentrations of drugs against absorbance was plotted to obtain a calibration curve. Both the drugs obey Beer's law individually and in mixture within the concentration range of 5-50 μg/ml. The absorptivity values (A 1%, 1 cm) of each drug at selected wavelengths were determined. The concentration of each drug in laboratory mixture was determined by substituting the absorbance and absorptivity values in the following equations, Cx = (Qm-Qy/Qx-Qy) × A/Ax 1 and Cy = (Qm-Qx/Qy-Qx) × A/Ay 1 17 , where, Cx is the concentration of LAN, Cy is the concentration of DOM, Qm is the ratio of absorbance of sample at selected wavelengths, Qx is the ratio of absorptivity of LAN, Qy is the ratio of absorptivity of DOM, Ax 1 is A (1%, 1 cm) of LAN at 256.0 nm, Ay 1 is A (1%, 1 cm) of DOM at 256.0 nm.
The prior criteria for two wavelength method (method B) are existence of two such wavelengths where interfering component shows same absorbance whereas component of interest shows significant difference in absorbance. Based on this criterion, two wavelengths 277.6 nm and 302.1 nm were selected as λ 1 and λ 2 for estimation of LAN at which DOM shows same absorbance but LAN shows significant difference in absorbance. Similarly, wavelengths 231.3 nm and 292.0 nm were selected as λ 1 and λ 2 for estimation of DOM. For calibration curve, the standard stock solutions of these drugs were diluted in the concentration range of 10-100 μg/ml and absorbances were recorded at selected wavelengths. Both the drugs obey Beer's law individually and in mixture within the concentration range of 5-50 μg/ml. From standard stock solutions fi ve laboratory mixtures (samples) and one as standard were prepared containing 30 μg/ml of LAN and 10 μg/ml of DOM. The absorbance of the resulting solutions were measured at the selected wavelengths and concentration of each drug was determined using the following equation, Cu = Au/As×Cs/Cu, where, Cu is the concentration of unknown, Cs is the concentration of standard, Au is the absorbance of unknown, As is the absorbance of standard and d is the dilution factor.
For analysis of capsule formulation, twenty capsules (Leedom manufactured by Bestochem Formulation (I) Ltd. and Lans-DX manufactured by Zydus Recon Healthcare Ltd. India) were weighed, contents removed and fi nely powdered. For method A, quantity of powder equivalent to 30 mg of LAN and 10 mg of DOM was weighed accurately and to it 20 mg of pure DOM was added (standard addition method). The mixture was dissolved in solvent and fi ltered with 0.45 μ membrane fi lter paper. An aliquot of fi ltrate was pipetted and diluted to obtain concentrations 30 μg/ml of LAN and 10 μg/ml of DOM. The absorbance of resulting solutions was measured at selected wavelengths. For method B, a calibration curve of seven mixed standards was prepared by plotting the concentrations of drugs against absorbance difference at selected wavelengths. A quantity of powder equivalent to 30 mg of LAN and 10 mg of DOM was weighed accurately, dissolved in solvent and fi ltered. The fi ltrate was diluted further to obtain a concentration of 30 μg/ml of LAN and 10 μg/ml of DOM. The absorbances of the resulting solutions were recorded at the selected wavelengths and concentration of each drug was obtained by extrapolating the absorbance value on standard calibration curve of mixed standards.
The recovery studies were carried out at different concentrations by spiking a known concentration of standard drug to the pre-analyzed sample and contents were reanalyzed by proposed methods. The results of marketed formulation analysis and recovery studies are depicted in Table 1. The methods were validated statistically as per ICH/USP 16 guidelines for parameters like accuracy, precision, ruggedness, specificity, linearity and range (Table 2). Accuracy was ascertained on the basis of recovery studies. Precision was studied by analyzing fi ve replicates of sample solutions and concentrations were calculated. Ruggedness was established by carrying out experiment at different conditions like intra day, inter day and by different analyst. Specificity of methods was ascertained by analyzing the solutions under different stress conditions like basic (0.1 N NaOH, 1.0 ml, 40°), oxidation (3% v/v H 2 O 2 , 1.0 ml, 40°), heat (60°) for 24 h. Linearity and range were determined by analyzing 80-120% of test concentrations of each drug.
In the proposed method for analysis of LAN and DOM in commercial formulation a mixture of methanol and 0.1 M NaOH is used as the solvent. The overlain spectrum of LAN and DOM does not give any suitable isoabsorptive point in a concentration proportion of 3:1 respectively whereas the overlain spectra of both drugs in 1:1 ratio (30 μg/ml of each drug) shows a reproducible isoabsorptive point at 256.0 nm. Hence standard addition technique was employed in order to bring a concentration ratio of 1:1 (30 μg/ml).