Effect Of Ultra Violet Radiation On The Stability Of Proguanil And Pyrimethamine

The influence of UV radiation (366nm) on thestability of proguanil hydrochloride and pyrimethaminesulphate in tablet formulations and in phosphatebuffer solutions of different pH values has beenevaluated in the present study, UV spectroscopicmethod for estimating drug content in the variousdosage forms was employed. The effect of pH on theUV spectrum of the drugs was investigated» Theinfluence of reaction vessel and pH on the irradiatedphosphate buffer solutions was also studied,In-vitro dissolution rate studies of the drugswere carried out including those tablets that hadbeen subjected to UV irradiation.The UV spectrum of proguanil hydrochloride wasfound to be stable at pH values above 2.0 in phosphatebuffer solutions. Below pH 2,0 the spectral peak at232nm disappeared while the peak at 253nm flattenedout giving a plateau.Proguanil hydrochloride was found to enter intophotochemical reaction in phosphate buffer solutionwhen subjected to continuous UV irradiation at 366nm.Evidence of photochemical reaction was shown by lossof spectral peaks in phosphate buffer, appearance ofa precipitate, colour change of solution, spectralshift and increase in absorbance of the irradiatedsolution. The photochemical reaction was found to beinfluenced by the pH of the solution and the type of glassware in which the reaction was performed.Assay of irradiated proguanil hydrochloride tabletsindicated loss of drug content with time.Dissolution rate studies of the irradiated tabletsshowed decrease in dissolution rate: with timeThe UV spectrum of pyrimethamine sulphate remainedstable at different Values. Pyrimethamine sulphateappeared not to readily enter into photochemicalreaction. The formulations used showed signs ofdegradation by colour change of tablets but there wasno loss of drug content on assay.The dissolution rate of the irradiated pyrimethaminetablets produced by Wellcome Nig. Ltd. increased withtime in phosphate buffer solution pH 4.5 while thedissolution rate of irradiated pyrimethamine tabletsproduced by Quality Control Unit A.B.U. Zaria decreasedwith time in phosphate buffer solution pH 4.5. Thisdifference observed in the dissolution rates of theformulations has been attributed to the influence ofthe different excipients used by the differentmanufacturers.

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