INTRODUCTION:

Atorvastatin calcium (ATR) is [R-(R*, R*)]-2-(4-fluorophenyl)-β, δ-dihydroxy-5-(1-methylethyl)-3-phenyl-4-[(phenylamino) carbonyl]-1Hpyrrole-1-heptanoic acid, calcium salt (2:1) trihydrate is an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. This enzyme catalyzes the conversion of HMG-CoA to mevalonate, an early and rate-limiting step in cholesterol biosynthesis^1,2.

Felodipine (FE) is a dihydropyridine derivative that is chemically described as ± ethyl methyl 4-(2,3-dichlorophenyl)-1,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylate. It is a calcium-channel blocker used in the treatment of hypertension and angina pectoris^3,4. Being a dihydropyridine derivative Felodipine has the advantage of being more selective as vasodilator and having less cardiac effects than non-dihydropyridine calcium antagonists^5-7.

Calcium channel blockers and statins combination decreases smooth muscle cells proliferation, oxidative stress, inflammation, apoptosis, matrix metalloproteinase production and increase nitric oxide production. Having synergistic effect of calcium channel blockers with lipid-lowering therapy in retarding progression of coronary atherosclerosis^8,9. Literature survey revealed that there is no UV method has been reported yet for the simulataneous analysis of these two drugs.

MATERIALS AND METHODS:

Pure drugs Atorvastatin calcium and Felodipine were received as gift samples from MMC Healthcare, Solan, Himachal Pradesh and all other chemicals were used of analytical grade.

Instrumentation

The present work was carried out on Shimadzu UV- 1700 series spectrophotometer having double beam detector configuration. The absorption spectra of reference and test solution were carried out in a 1 cm quartz cell over the range of 200-400 nm.

Experimental condition

According to the solubility characteristics of drug a combination of methanol and 0.1N HCl in 1:9 ratio was selected as solvent for analysis.

Figure:1. Structure of Atorvastatin calcium

Figure:2. Structure of felodipine

Standard solution:

UV analysis was done by using the standard stock solution of 1000µg/ml of each ATR and FE by dissolving 100mg of each standard drug separately in mixture of methanol and 0.1N HCl in 1:9 ratio in 1:9 ratio. Aliquots of 2, 4, 6, 8, 10µg/ml were prepared by using this stock solution, for the preparation of calibration curve.

Preparation of sample solution:

Twenty tablets, each containing 10mg of ATR and 5 mg of FE were weighed and average weight was calculated. Quantity equivalent to 10mg of Atorvastatin calcium and 5mg of Felodipine were weighed, transferred to a 100 ml volumetric flask, extracted and made upto volume with methanol and 0.1N HCl in 1:9 ratio in 1:9 ratio and filtered. From this solution, suitable aliquots were prepared, scanned in UV region and absorbances were noted at selected wavelengths. The amounts of ATR and FE were calculated using the formula given below.

A₁ = Absorbance of formulation at 241nm

A₂ = Absorbance of formulation at 366.5nm

ax₁= Absorptivity of Atorvastatin calcium at 241nm

ax₂= Absorptivity of Felodipine at 366.5nm

ay₁= Absorptivity of Atorvastatin calcium at 241nm

ay₂ = Absorptivity of Felodipine at 366.5nm

C_ATR = Concentration of Atorvastatin calcium

C_FE = Concentration of Felodipine

Selection of wavelength:

For Estimation of ATR wavelength 241nm was selected and calibration curve (n = 6) was plotted in the range of 2-10µg/ml between absorbance and concentration. FE was estimated at 366.5nm, where ATR shows no interference. Calibration curve was plotted between absorbance and concentration.

Linearity:

The linearity for spectrophotometric method was established in the concentration of 2, 4, 6, 8, 10µg/ml for both the drugs.

Method validation:

Accuracy was determined by recovery study. The recovery experiment was carried out by spiking the already analyzed sample of the tablets with their different known concentration of standard ATR and FE. Precision for assay were determined by repeatability, inter day, intra day precision for both drugs, each in three replicate¹⁰.

RESULTS AND DISCUSSION:

Linearity:

The linearity for spectrophotometric method was established in the concentration of 2, 4, 6, 8, 10µg/ml for both the drugs, absorbances at 241 for ATR and 366.5 for FE.

Figure:3 Absorption spectrum of Atorvastatin calcium

Figure: 4 Calibration graph of Atorvastatin calcium at 241nm

The absorbances of different concentrations of ATR were noted at the selected wavelength 241nm. Calibration curves were plotted using concentration Vs absorbance. Slope, intercept and correlation coefficient values were found to be 0.097, 0.022 and 0.998 respectively.

Figure:5 Absorption spectrum of Felodipine

Figure: 6 Calibration graph of Felodipine at 366.5nm

Felodipine was found to be linear between the range 2-10µg/ml. The absorbances of these solutions were noted at the selected wavelength 366.5nm. Calibration curves were plotted using concentration Vs absorbance.. Slope, intercept and correlation coefficient values were found to be 0.023, 0.002 and 0.999, respectively.

Precision:

Precision studies were performed by preparing the standards six times and measuring the absorbances of drugs at 241 nm and 366.5 nm. Low %RSD shows that the method has good precision. The results are given in table 1 and 2.

Table: 1 Intra day precision studies

Concentration (μg/ml)	Time	Absorbance		% RSD
		ATR	FE	ATR	FE
ATR 6µg/ml and Felodipine 10μg/ml	9.30	0.623	0.342	0.322	0.8849
	12.30	0.621	0.339
	3.30	0.619	0.336

Table: 2 Inter day precision studies

Concentration (μg/ml)	Time	Absorbance		% RSD
		ATR	FE	ATR	FE
ATR 6µg/ml and Felodipine 10μg/ml	1	0.625	0.349	0.806	1.494
	2	0.620	0.342
	3	0.615	0.339

Stability studies

Stability studies of the drug solutions were carried out and they were found to be stable at room temperature for about 7 hours, table 3.

Table: 3 Stability studies

Concentration (μg/ml)	Time (min)	Absorbances of the drug
Concentration (μg/ml)	Time (min)	ATR (241nm)	FE (366.5nm)
ATR 6µg/ml and Felodipine 10μg/ml	0	0.629	0.346
	60	0.628	0.342
	180	0.625	0.339
	300	0.621	0.336
	420	0.618	0.332

Recovery studies:

In order to ensure the suitability and reliability of proposed method, recovery studies were carried out. To an equivalent quantity of formulation powder, a known quantity of standard Atorvastatin calcium and Felodipine were added at 50% and 100% level and the contents were re-analysed by the proposed method. The % recovery and %RSD were calculated.

Recovery was calculated by using following formula

%Recovery=

Table: 4 Recovery studies

Level	% Recovery		% RSD*
Level	ATR	FE	ATR	FE
50%	101.57	100.23	0.636	0.542
100%	99.63	98.48	0.543	0.652

* %RSD (relative standard deviation) of six observations

The recovery for ATR ranges from 99% - 101% and for Felodipine ranges from 98% - 100%.

CONCLUSION:

The proposed spectrophotometric method is accurate, precise and reliable for the simultaneous measurement of ATR and FE in combined dosage form. The developed spectrophotometric method was validated for simultaneous estimation of ATR and FE using linearity, range, accuracy and precision. The RSD for all parameters was found to be less than two, which indicates the validity of method and assay results obtained by this method are in fair agreement. The developed method can be used for routine quantitative simultaneous estimation of ATR and FE in multi-component pharmaceutical preparation.

ACKNOWLEDGMENT:

We wish to thank to MMC Healthcare, Solan, Himachal Pradesh for providing gift sample and to the management of Sree Vidyanikethan College of pharmacy for providing the necessary facilities to carry out my research work.

REFERENCES:

1. Corsini. A, et al., New insights into the pharmacodynamic and pharmacokinetic properties of statins, Pharmcol. Ther. 84 (1999) 413–428.

2. Lennernas. H, Clinical pharmacokinetics of atorvastatin, Clin. Pharmacokinet. 42 (2003) 1141–1160.

3. Yedinak. K. C, et al.,. Felodipine: a new dihydropyridine calcium channel antagonist. DICP, 1991, 25: 1193-1206.

4. Walton. T, et al., Felodipine and isradipine: new calcium-channel-blocking agents for the treatment of hypertension. Clin. Pharm., 1993, 12: 261-275.

5. Little. W. C, et al., Vascular selective calcium entry blockers in the treatment of cardiovascuolar disorders: focus on felodipine. Cardiovasc. Drugs Ther., 1995, 9: 657-663.

6. Song. H, Bao. W, et al., Effects of extended release felodipine on endothelial vasoactive substances in patients with essential hypertension. Clin. Chem. Lab. Med., 2008, 46: 393-395.

7. Yao. R, Cheng. X, Liao. Y. H, Molecular mechanisms of felodipine suppressing atheroscelerosis in high-cholesteroldiet apolipoprotein E-knockout mice. J. Cardiovasc. Pharmacol., 2008, 51: 188-195.

8. Jose Luis Martin Ventura, et al., Vascular Protection of Dual Therapy (Atorvastatin- Amlodipine) in Hypertensive Patients. J Am Soc Nephrol 17, S189–S193.2006.

9. Wouter Jukema. J, et al., Proposed Synergistic Effect of Calcium Channel Blockers with Lipid-Lowering Therapy in Retarding Progression of Coronary Atherosclerosis. Cardiovascular Drugs and Therapy, 12:111–118.1998.

10. ICH Giudelines, Q2B, Analytical Method Validation, www.ich.org

Received on 24.05.2011 Modified on 05.06.2011

Asian J. Research Chem. 4(8): August, 2011; Page 1202-1205