Study on the related substance of lamivudine by a validated HPTLC method in oral dosage forms

Lamivudine is an anti-retroviral drug available in the formulation of tablets and oral solution. The selected compound Salicylic acid is categorized as Lamivudine impurity C. An HPTLC method was developed and validated for the estimation of Lamivudine in bulk and oral dosage forms. The chromatograms were developed using a mobile phase of methanol: water: ethyl acetate in the ratio 4:2:4, v/v/v on pre-coated plate of silica gel 60 F₂₅₄ and quantified by densitometric absorbance mode at 233nm. The R_f values were 0.76±0.03 and 0.65±0.02 for Lamivudine and Salicylic acid respectively. The linearity was found to be within the range of 500-3000 ng/band for Lamivudine and 50-300ng/band for Salicylic acid. The lower limits of detection and quantification were 21.24ng/band and 64.37ng/band for Lamivudine and 8.47ng/band and 25.68ng/band for Salicylic acid. The statistical evaluation by the %RSD calculation for accuracy and precision were below 2. The validated method was applied to detect and quantify Salicylic acid in the tablets of two dosage forms and the oral solution prepared as admixture. The quantified amount of the impurity C was found to be within the limits in the tablets and not detectable in the oral solution. This method can be adopted to determine Lamivudine and its impurity C in the API and different dosage forms.