INTRODUCTION:

Finasteride ^[1] (FIN) chemically is, N- (1,1-dimethylethyl) –3-oxo-4-aza-5-androst-1-ene- 17-carboxamide (Fig.1) is a type II 5 alpha reductase inhibitor, slowly reduces prostatic volume. Prostate growth and function is influenced by dihydrotestosterone, 5 alpha-reductase enzyme converts testosterone to dihydrotestosterone. Inhibition of 5 alpha reductase results in decreased level of dihydrotestosterone leading to reduction of prostate size.

Fig 1. Structure of Tamsulosin

Tamsulosin ^[2] (TAM) chemically is, 5- [(2R)-2[[2-(2-Ethoxy Phenoxy) ethyl] amino] Propyl} - 2-methoxy benzene sulfonamide (Fig. 2) is a selective alpha 1 adrenoceptor blocking agent. Smooth muscle tone is mediated by the sympathetic nervous stimulation of alpha1 adrenoceptors, which are abundant in the prostate, prostatic capsule, prostatic urethra, and bladder neck. Blockade of these adrenoceptors can cause smooth muscles in the bladder, neck and prostate to relax, resulting in an improvement in urine flow rate and reduction in symptoms of benign prostatic hyperplasia ^{[3, 4]} (BPH).

Fig 2. Structure of Finasteride

According to the literature survey it was found that few analytical methods such as Visible ^[5], UV^[6,7], polarographic analysis^[8] and HPLC methods^[9-14] were reported for finasteride and tamsulosin, but not even a single method has been reported on Second derivative spectroscopic method. The objective of this study was to develop and validate a simple and specific Second derivative spectrophotometric method for the simultaneous determination of tamsulosin and finasteride in combined dosage form. Derivative spectroscopy has been widely used as a tool for quantitative analysis. This technique offers various advantages over the conventional spectrophotometric methods, such as discrimination of the sharp spectral features over the large bands and the enhancement of the resolution of the overlapping spectra. This method exhibited a precise, accurate and cost effective assay for these drugs in mixture.

MATERIALS AND METHOD:

Chemicals: 0.1N Hydrochloric acid, 0.1N Sodium hydroxide, Water, Acetonitrile, Methanol.

Drugs: Tamsulosin, finasteride and formulation (URIMAX-F).

Instrument: Shimadzu UV–Visible spectrophotometer (model UV-1800).

Selection of solvent:

The derivative spectra’s of tamsulosin and finasteride in different solvents like water, acetonitrile, sodium hydroxide and hydrochloric acid did not show any favorable zero crossing points, but when dissolved in methanol the derivative spectra’s of both drugs showed zero crossing points. Hence methanol was selected as the solvent for the method.

Selection of derivative method:

Though both first and second derivative spectra’s showed zero crossing points in methanol solvent and their absorbance’s were considerably better, but the second derivative method was selected because the spectral characteristics and resolution were good in the second derivative spectra.

Selection of wavelengths (Zero crossing points):

The zero crossing points of tamsulosin were 222, 232 and 235 nm and for finasteride were 219, 239, 241 nm. Out of these wavelengths 232 nm for tamsulosin and 239 nm for finasteride were selected as the zero crossing points for the method based on their linearity data. At 232 nm tamsulosin showed zero absorbance but finasteride had considerable absorbance. Similarly at 239 nm finasteride showed zero absorbance but tamsulosin had considerable amount of absorbance.

Preparation of Standard stock solutions:

Standard tamsulosin stock solution was prepared by dissolving 10 mg of drug in 100 ml of methanol to get a concentration of 100 μg ml^-1. Standard finasteride stock solution was prepared by dissolving 125 mg of drug in 100ml of methanol to get a concentration of 1250 μg ml^-1. The standard solutions were prepared by dilution of the stock solution with methanol.

Validation Parameters ^{[15, 16]}

Linearity:

To construct Beer’s law plot for finasteride and tamsulosin different aliquots of finasteride (1-8 ml) with different concentrations (12.5, 25, 37.5, 50, 62.5, 75, 87.5 and 100 μg ml^-1) and tamsulosin (0.1-0.8 ml) with different concentrations (1, 2, 3, 4, 5, 6, 7 and 8 μg ml^-1) were prepared by serial dilutions with methanol from the individual stock solutions. Then absorbance of the solutions was measured at 232 nm for finasteride and 239 nm for tamsulosin. The standard overlain spectrum of tamsulosin and finasteride was shown in Fig 3. The linearity values were shown in Table 1

Fig 3. Overlain Second derivative spectra of standard drugs(Tamsulosin 2 µg ml^-1 and finasteride 25 µg ml^-1)

Table No 1. Linearity :

Parameters	Tamsulosin	Finasteride
Concentration(µg/ml)	1-8	12.5-100
Slope	0.001	0.0001
Intercept	0.000	0.0001
Correlation coefficient (r²)	0.999	0.999

Table No 2. Recovery Studies:

Drug	Amount added (µg ml^-1)	Amount recovered (µg ml^-1)	% Recovery
Finasteride	12.5	12.47	99.76
	10	9.95	99.50
	15	14.94	99.60
Tamsulosin	1	0.991	99.10
	0.8	0.793	99.12
	1.2	1.19	99.16

Recovery studies:

The recovery studies were carried out at three different levels i.e. 80%, 100% and 120%. To ensure the reliability of the above method, recovery studies were carried out by mixing a known quantity of standard drug with the pre analysed sample formulation and the contents were reanalyzed by the proposed method. The percentage recovery values were shown in Table 2.

Precision:

The precision of the method was established by carrying out the analysis of the analytes using the proposed developed method. The low value of standard deviation showed that the methods were precise. The results were shown in Table 3.

Specificity:

Comparison second derivative spectrum of tamsulosin and finasteride in standard and drug formulation solutions showed that the wavelength of maximum absorbance did not change. According to the results obtained by recovery study, the derivative spectrophotometric method is able to access the analyte in presence of excipients and hence, it can be considered as specific method.

LOD and LOQ:

The limit of Detection (LOD) and limit of Quantification (LOQ) of the developed method were determined by injecting progressively low concentrations of the standard solutions. The LOQ of tamsulosin and fnasteride was found to be 0.6 µg ml^-1and 1 µg ml^-1respectively and the LOD was found to be 0.08 µg ml^-1 and 0.3 µg ml^-1respectively.

Ruggedness:

The ruggedness test of analytical assay method is defined as degree of reproducibility of assay results obtained by the successful applications of assay over different time, day and among multiple analysts. The results showed no statistical differences suggesting that the developed method was rugged

Preparation of Test Solutions and Estimation of Finasteride and Tamsulosin in formulation:

For analysis of commercial formulations, 20 capsules (Urimax F containing 0.4mg TAM and 5mg FIN) were weighed, powdered and weight equivalent to 12.5 mg of finsateride and 1 mg of tamsulosin was taken and transferred into a volumetric flask and made up to 100ml with methanol, sonicated for 5min, filtered and further diluted with methanol to get the concentrations within the linearity range of respective drugs and measured the absorbance’s at 232 nm for finsateride and 239 nm for

tamsulosin respectively. The formulation spectrum was shown in Fig 4. Then the amount of drug present in

formulation was calculated and the results were shown in Table 4.

Table No 4. Analysis of Formulation:

Drug

name

Amount

labeled

(mg ml^-1)

Amount

estimated

(mg ml^-1)

% Label

claim

Deviation

Finasteride

5mg

4.95

99.00

(-) 1.0

Tamsulosin

0.4mg

0.397

99.25

(-) 0.75

Fig .4 Second derivative spectra of formulation (Tamsulosin 2 µg ml^-1 and finasteride 25 µg ml^-1)

RESULTS AND DISCUSSION:

From the optical characteristics obtained with the proposed method it was found that the drug obeys linearity with in concentration range of 12.5-100 μg ml^-1 for FIN and 1-10 μg ml^-1 for TAM. From the precision studies, it was found that the percent relative standard deviation (%RSD) is less than 2% which indicates that the method has good reproducibility. From the results of recovery studies, it was found that the percent recovery values of pure drug from the preanalysed solutions of formulations were in between 98.0-99.8%, which indicates that the method is accurate and reveals that commonly used excipients and additives present in the pharmaceutical formulations did not interfere in the proposed method. The proposed method was simple, sensitive and reliable with good precision and accuracy. Hence, this method can be used for the routine analysis of Finasteride and tamsulosin in bulk samples and pharmaceutical formulations.

CONCLUSION:

A convenient and rapid UV method has been developed for simultaneous estimation of finasteride and tamsulosin in available dosage form. The assay provides a linear response across a wide range of concentrations. Low intra-day and interday % RSD coupled with excellent recoveries. Hence, this method can be easily and conveniently adopted for routine analysis of Finasteride and Tamsulosin in pure form and its dosage forms

ACKNOWLEDGEMENT:

I am very much thankful to School of pharmacy, Anurag Group of Institutions, Hyderabad, for giving permission to carry out my research work.

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Received on 09.08.2012 Accepted on 30.08.2012

Asian J. Pharm. Ana. 2(3): July-Sept. 2012; Page 73-76

Drug	Concentration (µg ml^-1)	Intra-day conc. Measured		Inter-day conc. Measured
Drug	Concentration (µg ml^-1)	Mean (µg ml^-1)	*% RSD**	Mean(µg ml^-1)	*%RSD**
Finasteride	25	25.06	0.641	25.08	0.962
Tamsulosin	2	2.03	0.874	2.04	0.891