STABILITY-INDICATING SPECTROPHOTOMETRIC METHODS FOR THE DETERMINATION OF PRAMIPEXOLE DIHYDROCHLORIDE

Six simple, reproducible and efficient stability-indicating methods are presented for the quantitative estimation of pramipexole dihydrochloride in presence of its degradation products. The first method is based on direct spectrophotometric determination of the intact drug at 263.4 nm as the degradation product shows nearly zero crossing at this wavelength. The second one is dual wavelength method in which two wavelengths 270 nm and 290 nm were selected for the estimation of intact pramipexole in presence of its degradation product as the oxidative degradate shows the same absorbance at these wavelengths. Whilst the third one is bivariate method depend on a simple mathematical algorithm . The fourth method depends on the use of first derivative of the ratio spectra where the amplitude of the first derivative trough of (pramipexole / degradate) is measured at 282.2nm. The fifth one is ratio difference method, based on measurement of peak amplitudes between two selected wavelengths in the ratio spectra at 270 and 285 nm. Finally, the last one depends on mean centering of the obtained ratio spectra and the concentration of the drug was determined by measuring the amplitude at 300 nm. Regression analysis of Beer’s plots shows good correlations (r = 0.9997 - 0.9999) over concentration ranges of 5-50 μg mL -l of the intact drug. The proposed methods can be used as stability indicating ones to determine the intact drug in presence of its oxidative induced degradation products up to 60 - 80%. They are also successfully applied to analyze pramipexole in its formulation; Ramexole ® tablets with mean recoveries ranging from W