Simultaneous Determination of Ritonavir and Lopinavir in Human Plasma after Protein Precipitation and LC-MS-MS

A simple, rapid, specific and sensitive method has been developed and validated for simultaneous determination of lopinavir and ritonavir in human plasma. The analytical procedure involves a protein precipitation method using fluoxetine as internal standard Separation was carried out on an Inertsil ODS column using a mobile phase consisting of acetonitrile and 5 mM ammonium acetate buffer. The total run time of analysis was 2.0 min. A linear response function was established for the range of concentrations 50.67-10,008.82 ng mL⁻¹ for lopinavir and 5.066-1,000.693 ng mL⁻¹ for ritonavir. The method was successfully applied to an oral bioequivalence study in humans.