A new spectrophotometric method for the determination of finasteride in tablets

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Abstract

A simple, rapid, accurate, precise and sensitive colorimetric method for the determination of finasteride in tablets is described. The proposed methods are based on the formation of ion-pair complexes between the examined drug with bromophenol blue (BPB), bromocresol green (BCG) and bromothymol blue (BTB), which can be measured at the optimum λmax. Beer's law is obeyed in the concentration ranges 3.0–15.0, 3.0–15.0 and 5.0–20 μg/mL with BPB, BCG and BTB, respectively. The detection limits of FIN was found to be 1.16 μg/mL for BPB, 1.17 for BCG, 1.76 μg/mL for BTB. All the methods gave similar results and were validated for selectivity, linearity, precision and sensitivity. The proposed methods were directly and easily applied to the pharmaceutical preparation with accuracy, resulting from recovery experiments between 100.11 and 100.33% for BPB, 100.17 and 100.67% for BCG and 100.33 and 100.60% for BTB methods. The low relative standard deviation values indicate good precision and high recovery values indicate accuracy of the proposed methods. The proposed methods have been applied to the determination of drug in commercial tablets. Results obtained from the analysis of commercial preparations with the proposed methods are in good agreement with those obtained with the official HPLC method.

Introduction

Finasteride (FIN); (5α,17β)-N-(1,1-dimethylethyl)-3-oxo-4-azaandrost-1-ene-17-carboxamid (Fig. 1) [1] is a potent 5α reductase inhibitor, that has been used to treat of men with benign prostatic hyperplasia [2], [3].

Several methods for the determination of FIN in pharmaceuticals have been reported in the literature including UV-spectrophotometric [4], gas chromatographic [5], high performance liquid chromatographic (HPLC) [6], [7] and polarographic [8].

For determination of FIN in different sample matrices (blood and semen) several methods are reported in the literature. Few reports describe HPLC [9], [10], [11] and high performance liquid chromatography–mass spectrometry (LC/MS/MS) [12], [13] methods for the determination in biological fluids of FIN. Guarna et al. [14] have studied synthesis and determined of FIN in human plasma at picogram level by an isotope-dilution mass spectrometric method.

Extractive spectrophotometric procedures are popular for their sensitivity in the assay of drugs and, therefore, ion-pair extractive spectrophotometry has received considerable attention for the quantitative determination of many pharmaceutical compounds [15], [16], [17], [18], [19], [20], [21], [22].

Simple, rapid and highly sensitive and robust spectrophotometric method is described, for the first time, for the determination FIN with BPB, BCG and BTB, respectively.

The present work describes colorimetric method which is superior to the reported ones, for rapidity, reproducibility, time consuming and high sensitivity.

Section snippets

Materials

FIN and its tablets (Propecia® 1 mg) were kindly supplied from Merck Sharp Dohme (Istanbul, Turkey). Bromophenol blue (BPB), bromothymol blue (BTB) and bromocresol green (BCG) were purchased from Merck (Darmstadt, Germany).

Analytical grade chloroform was used for extraction. Solvents and other chemicals were of analytical grade (Merck, Darmstadt, Germany).

Apparatus

A Shimadzu UV-160A UV–vis spectrophotometer with 1 cm glass cells was used. UV–vis spectra were automatically obtained by Shimadzu UV-160A

Results and discussion

In the present study, the reduced FIN possessing secondary aromatic amino group is protonated in acidic medium, which forms ion-pair complexes with each of the acid dyes such as BPB, BCG and BTB (Fig. 2).

The reaction between FIN and reagents (BTB, BCG and BPB) in phthalate buffer of pH 3.5 produces a yellow colored product. The absorption band of complexes showed λmax at 409.5, 410, and 411 nm for BTB, BCG and BPB, respectively (Fig. 3).

The reagent blanks prepared under similar conditions showed

Conclusion

The presented study proposes a simple, inexpensive, precise and accurate method for the determination of FIN in pharmaceutical preparation. The proposed methods were advantageous over other reported visible spectrophotometric and colorimetric methods.

The most striking advantage of the extractive spectrophotometric methods is the sensitivity, which surpasses the sensitivity of some of the previously reported methods [4], [5], [6].

A important advantage of the extractive spectrophotometric method

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