INTRODUCTION:

Atorvastatin calcium is Antilipidemic agent. It is selective, competitive inhibitor of HMGCoA reductase, the rate-limiting enzyme that converts 3-hydroxy-3-methylglutaryl-coenzyme A to mevalonate, a precursor of the sterols, including cholesterol. It is officially included in the Indian pharmacopoeia¹. Atorvastatin calcium Chemically [R-(R*, R*)]-2-(4fluorophenyl)-β, δ-dihydroxy-5-(1-methylethyl)-3 Phenyl-4-[(phenyl amino) carbonyl]-1H- Pyrrole-1-heptanoic acid^2-5. Literature survey reveals that RP-HPLC^6-8. Spectroscopy method⁹, and HPTL¹⁰, UPLC¹¹, methods have been reported for the determination of Atorvastatin calcium in pharmaceutical dosage form and in plasma^12,13. The objective of present work was to device a simple, precise, rapid and economical UV spectrophotometric methods estimation of atorvastatin calcium from marketed combined pharmaceutical dosage form^14-16.

EXPERIMENTAL:

Instrument, Chemicals, Reagents:

Shimadzu 1700 U.V visible spectrophotometer with 1cm matched quartz cells, and methanol was used for the experiment.

Atorvastatin Calcium Stock Solution:-

25 mg portions of standard atorvastatin calcium were weighed, transferred to 25 mL volumetric flasks, and dissolved in methanol (15 mL). The flasks were shaken, and the volume was made up to the mark with same solvent. A 1.0 mL aliquot was pipette into a 10 mL volumetric flasks separately, and methanol was added to adjust the volume to give a concentration of 100 μg/ml of Atorvastatin calcium.

Sample solution of pharmaceutical formulation (Tablet):

Sample solution: Twenty tablets of Atorvastatin calcium were weighed and powered in glass mortar. Amount equivalent to 10 mg was transferred to 100 ml volumetric flasks, dissolved in sufficient quantity of methanol, sonicated and made up the volume with methanol to obtain concentration of 100µg/ml. This solution was then filtered through Whitman filter paper # 41. Further dilutions were made from this stock solution to get required concentration.

Zero order spectroscopic method:

Determination of λmax:

The standard solution of Atorvastatin calcium (20µg/ml) was scanned at different concentrations in the range of 200-400nm and the λmax was found to be 247.5 nm against reagent blank. [Fig: 1].The absorbences were recorded for 03-30 μg/ml at 247.5nm (λ max).The calibration curve was plotted. (Fig no.2, Table No. 1)

Second Order Derivative Method:

Standard solution of Atorvastatin calcium were diluted appropriately with methanol to obtain solutions containing 12 [micro]g/mL. Spectra of these diluted solutions were scanned in the spectrum mode between 200 and 350 nm, These zero-order spectra of Atorvastatin calcium were treated to obtain corresponding second-order derivative spectra.(fig No.3)

Calibration Curve for Atorvastatin calcium:

The absorbances were recorded for 03-30 μg/ml at 217 nm in derivative mode. From this calibration curve was plotted. (Fig. 4)

Fig: 1 λmax Atorvastatin calcium

Fig :2 Calibration Curve of Atorvastatin calcium :

Fig 3: second order derivative of Atorvastatin calcium:

Fig :4 Calibration Curve for Atorvastatin calcium

Table No:1 Conc. of Atorvastatin

Sr. No.	Conc. of Atorvastatin	Absorbance at 247.5
1	3	0.101
2	6	0.212
3	9	0.333
4	12	0.461
5	15	0.582
6	18	0.693
7	21	0.820
8	24	0.938
9	27	1.052
10	30	1.171

Table:2 Optical Characteristics and Precision

Following are the parameters obtained during the procedure

Parameters	values	Values
Absorption maxima (nm)	247.5	217
Beer’s law limit (mcg/ml)	03-30	03-30
Correlation coefficient	0.9999	0.9999
Molar absorptivity (lit/mole/cm)	2.2307×10⁴	4.584×10³
Sandell’s sensitivity(mcg/sqcm/0.001)	0.025043	0.083269
Slope (m)	0.03984	0.011958
Intercept	0.02113	0.00524
% COV	0.0999	0.011958
Confidence limit with 0.05 level	0.001315	0.004533
LOD (ng/ml)	27.0	30
LOQ ((ng/ml)	192	200

Table:3 Results of analysis of Zero Order

Sr.No	Tablet	Label claim	% Estimated	% Recovery*
1	Marketed Tablet A	10	99.68	99.186
2	Marketed Tablet B	10	100.19	100.88

Table:4 Statistical analysis of results

Sr.No	Tablet	SD*	COV (%)*	SE*
1	Marketed Tablet A	0.759	0.7519	1.1882
2	Marketed Tablet B	0.7480	0.7437	0.5781

* Mean of three readings, SD-Standard deviation, COV-Coefficient of Variation, SE- Standard Error

Table :5 Results of analysis of Second Order.

Sr. No	Tablet	Label claim	% Estimated	% Recovery*
1	Marketed Tablet A	10	100.2969	101.6092
2	Marketed Tablet B	10	99.1664	100.3546

Table :6 Statistical analysis of results

Sr.

Tablet

SD*

COV (%)*

SE*

Marketed Tablet A

0.365305

0.365385

0.110908

Marketed Tablet B

0.36234

0.364243

0.109197

* Mean of three readings, SD-Standard deviation, COV-Coefficient of Variation, SE- Standard Error

Method Validation:^17-20

a. Specificity:-

Pure Atorvastatin calcium is spiked with common excipients and was assayed by proposed method and it was found that the assay results were unaffected by the presence of excipients.

b. Linearity:-

Linearity was observed in the range of 03-30 mcg/ml, for zero order and second order derivative respectively. The calibration curve proves coefficient of correlation (r) 0.9999, 0.99997, for zero order, second order derivative method respectively.

c. Sensitivity:-

High Molar absorptivity and low Sandell’s sensitivity for the respective method reveals that all these methods are highly sensitive.

d. System precision:–

% COV calculated from three replicate readings (absorbance values) at concentration (12 µg/ml) confirm the precision of the method.

e. Assay results:-

Two different brands of Atorvastatin calcium tablets were analysed by proposed methods, the percentage in tablet were determined and presented in the tabular form.. Assay results obtained are within limit.

f. Accuracy and precision:–

The low values of S.D, %COV, and 95% confidence interval indicate that method is precise. % recovery was found to be within limit indicate the noninterference from the formulation excipients and confirm the accuracy and precision of the method.

RESULTS AND CONCLUSIONS:

The methods Zero order (Table:3,4) and second order derivative(Table No.5,6,) method for the estimation of Atorvastatin calcium in tablet dosage were found to be simple, accurate and reproducible . Beer- lambert’s law was obeyed in the concentration range of 3-30 µg/ml in all these methods. The accuracy of the method was assessed by recovery studies at three different levels i.e. 80%, 100%, 120%. The values of standard deviation were satisfactory and the recovery studies were close to 100%. The %RSD value is less than 2 indicative of accuracy of the method. Results found are satisfactory and accepted as per norms.

ACKNOWLEDGEMENTS:

Authors are grateful to Emcure Pharmaceuticals Bhosari, Pune for providing the gift sample of atorvastatin calcium. We are also thankful to the Principal and Head of Pharmaceutical Chemistry Department of Government College of Pharmacy, Karad for providing the necessary facilities to carry out this work.

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Received on 25.11.2009 Modified on 20.01.2010

Asian J. Research Chem. 3(2): April- June 2010; Page 339-341