DEVELOPMENT OF UV SPECTROPHOTOMETRIC METHODS AND VALIDATION FOR ESTIMATION OF SIMVASTATIN IN BULK AND TABLET DOSAGE FORM BY ABSORBANCE MAXIMA AND AREA UNDER THE CURVE METHOD

Introduction: To develop two simple UV spectrophotometric methods for simultaneous estimation of Simvastatin (SMV) in bulk and tablet dosage form and validate as per ICH guidelines. Methods: Method A involved Absorbance maxima method which based on the measurement of absorbance of Simvastatin in methanol at λmax of Simvastatin 238 nm and Method B involved Area under the curve (AUC) method which based on the measurement of AUC in the range of 234-240 nm. Results: The developed methods were validated for linearity, precision, accuracy, LOD and LOQ as per ICH guidelines. Both the methods were found to be linear within the conc. range of 4-32 μg/ml for Simvastatin. Conclusion: The present methods were found to be simple, linear, precise, accurate and sensitive and can be used for routine quality control analysis for the estimation of Simvastatin in bulk and tablet dosage form.

Because of cost-effective and minimal maintenance, UV spectrophotometry is always preferred at small scale industries. Literature survey reveals that so far many UV spectrophotometric methods have been reported for the estimation of Simvastatin in alone or in combination with other drugs. But out of them only few methods included single estimation of Simvastatin. Therefore the main objective of the proposed methods were to develop simple, new and economic UV spectrophotometric methods for the estimation of Simvastatin in bulk and tablet dosage form and validate as per ICH guidelines.

Chemicals and Reagents
The pure API sample of Simvastatin was obtained as free gift samplefrom Gen Pharma Ltd; Pune respectively while solvent such as methanol used were of spectroscopy grade (E. Merck India) and double distilled water used for whole experiment. The marketed combined pharmaceutical dosage form ofSimvastatin (10 mg) i.e. Simvas (Micro Labs, India)was purchased from local market.

Instrumentation
A Jasco double beam UV-visible spectrophotometer, Model: V-630, with a fixed bandwidth (2nm) and 1-cm quartz cell was used for Spectral and absorbance measurements.
Preliminary solubility studies of drug 1 gm of Simvastatin was weighed and solubility was checked in 10 ml water, methanol, 0.1N NaOH and 0.1 N HCl. The drug was found to be freely soluble in methanol and practically poorly soluble in water, 0.1N NaOH and 0.1 HCl. Therefore methanol was selected as diluent and Simvastatin was also found to be stable in methanol for 48 hours in stability studies.

Preparation of calibration curve
From above std. stock solution of Simvastatin (100 µg/ml), pippete out aliquots 0.4 to 3.2 ml of Simvastatin and transferred to series of 10 ml volumetric flasks and final volume made upto mark with methanol as diluent to form solutions of 4 to 32µg/ml of Simvastatin. These solutions were then scanned in the range of 200-400 nm against diluent as blank. The absorbance maxima (λmax) were found to be 238 nm for Simvastatin and then calibration curve was plotted as absorbance vs concentration.

Sample preparation for analysis of Tablet formulation
Twenty tablets (Simvas) containing 10 mg of Simvastatin weighed, average weight calculated and triturated to fine powder and then weight equivalent 10 mg of Simvastatin transferred to 100 ml of volumetric flask containing proposed diluent, then sonicated for 15 minutes and filtered through Whatman filter paper no. 42 to form 100µg/ml of Simvastatin stock solution of and final volume made upto mark with diluent. From this, 1 ml of aliquot transferred in 10 ml of volumetric flask containing diluent to form 10µg/ml of Simvastatin stock solution and scanned in the range of 200-400 nm against methanol as blank at 238 nm and then drug content of solution was calculated by using standard calibration curve.

Absorbance maxima method
For the selection of analytical wavelength, standard solution of Simvastatin was scanned in the spectrum mode from 200 nm to 400 nm separately. From the spectra of drug, λmax of SMV, 238 nm was selected for the analysis (Fig. 2). Aliquots of standard stock solution were made and calibration curve was plotted.  The present UV spectrophotometric methods were validated for linearity, precision, accuracy, LOD and LOQ as per ICH guidelines [38] for estimation of Simvastatin in bulk and tablet dosage form.

Precision
Precision study expressed by carrying out Repeatability (intraday precision) and interday precision. The intraday (Repeatability) and interday precision study were carried out by estimating corresponding responses three times on the same day and on the three different days for the three different concentration for (8, 12 and 16µg/ml) for Simvastatin. The results of precision study were reported in terms of % relative standard deviation

Accuracy
The accuracy of developed method was carried out by calculating the % recovery of Simvastatin by standard addition method at three different levels i.e. 80 %, 100 % and 120 %. Known amount of standard solutions of SMV (9.6, 12 and 14.4µg/ml) were added to prequantitated sample solutions of 12µg/ml of SMV).

LOD and LOQ
Limit of detection (LOD) is defined as lowest concentration of analyte that can be detected while limit of quantitation is defined as lowest concentration of analyte that can be quantitated. With suitable precision and linearity, LOD and LOQ can be calculated from the following formulas LOD = 3.3* r / S and LOQ = 10 * r/ S Where r is the Standard deviation of y-intercept of the regression line and S is slope of the calibration curve.

Method development and optimization
The present study describes development and validation of two simple UV spectrophotometric methods for the estimation of Simvastatin in bulk and tablet dosage form using absorbance maxima method and area under the curve method. Solubility studies indicated that a Simvastatin shows better solubility in methanol solution as compared to solubility in distilled water and the λmax of Simvastatin was found to be 238 nm. Because of cost-effective and minimal maintenance, the present UV spectrophotometric methods can be preferred at small scale industries as compared to other reported methods.

Linearity
Linearity was evaluated by analysis of Std. SMV at Six different concentrations. SMV found to be linear within conc. range of 4-32µg/ml with regression coefficient of 0.9995 by the method A and 0.9992 by method B. The results of regression analysis are summarized in (Table 1). A result shows that within the concentration range mentioned above, there was an excellent correlation between peak area and concentration.  (Table 4).

LOD and LOQ
The limit of detection was found to be 2.09µg/ml and 2.82µg/ml for method A and for method B respectively. The limit of quantification was found to be 6.33µg/ml for method A and 8.56 µg/ml for method B respectively. Low values of LOD and LOQ indicates that the developed method was sensitive for the estimation SMV in bulk and tablet dosage form.

CONCLUSION
Simple UV spectrophotometric methods have been developed and validated for the determination of Simvastatin in bulk and tablet dosage form. The results of the validation parameters show that the UV spectrophotometric methods were found to be accurate, precise and sensitive. Because of cost-effective and minimal maintenance, the present UV spectrophotometric methods can be preferred at small scale industries and successfully applied and suggested for the quantitative analysis of Simvastatin in pharmaceutical formulations for QC, where economy and time are essential and to assure therapeutic efficacy.