DEVELOPMENT OF UV SPECTROPHOTOMETRIC FIRST ORDER DERIVATIVE METHOD FOR THE SIMULTANEOUS ESTIMATION OF RITONAVIR AND LOPINAVIR IN COMBINED TABLET DOSAGE FORM

A simple, accurate, precise analytical method has been developed for the simultaneous estimation of ritonavir and lopinavir in pure bulk drug and in combined tablet dosage form by UV spectrophotometry by first order derivative method. The standard solutions of ritonavir and lopinavir were prepared in acetonitrile followed by further required with the same solvent.  The solution containing ritonavir and lopinavir (20µg/mL and 80µg/mL) were scanned between 400 nm to 200 nm and from the overlain first order derivative graph it appeared that ritonavir showed zero crossing at 278.10 nm while lopinavir showed zero crossing at 246.70 nm. At zero crossing point of ritonavir (278.10 nm), lopinavir showed a measurable derivative absorbance where as at the zero crossing point of lopinavir (246.70 nm), ritonavir showed appreciable derivative absorbance value. Thus both the drugs do not interfere in the quantitation of one another. Calibration graphs showed linearity at the concentration ranges from 5-30 mg/ ml by ritonavir and from 20-120 mg/ ml by lopinavir. Corresponding regression equations of both the drugs were used for the determining their concentration. In the bulk drugs, ritonavir and lopinavir were estimated as 99.54% and 100.07% respectively whereas in the marketed tablets ritonavir was found as 98.17 % and lopinavir as 101.6 %. The results of analysis have been validated as per ICH guidelines and were found to be satisfactory. Hence, present study gives excellent method for the determination of both the drugs in combined tablet formulation.