Titrimetric and spectrophotometric determination of lamivudine in pharmaceuticals

Three new methods are described for the assay of lamivudine in bulk drug and in tablet dosage forms using chloramine-T and two dyes, methyl orange and indigo carmine, as reagents. In titrimetry, aqueous solution of lamivudine is treated with a measured excess of chloramine-T in sulphuric acid medium and after the oxidation of lamivudine is judged to be complete, the unreacted oxidant is determined iodometrically. Spectrophotometric methods entail the addition of a known excess of chloramine-T to lamivudine in hydrochloric acid medium followed by determination of residual oxidant by reacting it with a fixed amount of either methyl orange and measuring the absorbance at 520 nm (Method A) or indigo carmine and measuring the absorbance at 610 nm (Method B). In all the methods, the amount of chloramine-T reacted corresponds to the amount of lamivudine. Titrimetric method is applicable over 3.5-10 mg range. In spectrophotometric methods, the systems obey Beer’s law for 0.1-1.0 and 0.25-3.5 μg mL for method A and method B, respectively. Intra-day and inter-day precision and accuracy of the developed methods were evaluated. The methods were successfully applied to the assay of lamivudine in tablet formulations and the results were compared with those of a reference method by applying Student’s tand F-tests. No interference was observed from common tablet adjuvants.