Comparison of supercritical fluid chromatography and reverse phase liquid chromatography for the impurity profiling of the antiretroviral drugs lamivudine/BMS-986001/efavirenz in a combination tablet.

Dual and triple combinations of antiretroviral drugs are a cornerstone of human immunodeficiency virus type 1 (HIV-1) treatment. Supercritical fluid chromatography (SFC) and reverse phase liquid chromatography (RPLC) methods have been developed for the impurity profiling of a prototype combination tablet containing three such drugs: lamivudine, BMS-986001 and efavirenz. Separation by SFC was achieved using a Princeton 2-ethyl pyridine stationary phase and a mobile phase B consisting of methanol with 10 mM ammonium acetate and 0.1% isopropyl amine. This combination of mobile phase additives was required for both the separation of minor components and to minimize peak tailing of the active pharmaceutical ingredients (APIs). Separation by RPLC was achieved using a Discovery HSF5 stationary phase and a mobile phase consisting of 10 mM ammonium acetate, pH 5.5 and methanol. Mobile phase gradient elution was employed in each case to elute components with a wide range of polarities. Both these methods were found to have advantages and disadvantages. Out of the three APIs and 13 possible impurity/degradation products selected, all were resolved by RPLC. By SFC, 15 peaks were resolved with one co-eluting pair and a high degree of orthogonality was achieved relative to RPLC. A more even distribution of peaks across the separation space, a non-sloping baseline and fewer system peaks were significant advantages associated with the SFC method. Particular attention had to be paid to optimizing the reverse phase diluent strength/initial mobile phase composition to avoid distortion of the peak shapes for early eluting components. This was not an issue with SFC, as the diluent of choice (methanol) was also the solvent of choice (in combination with ≤20% water) for the dissolution of the triple combination tablet. As with RPLC, SFC was found to exhibit the required sensitivity for successful quantitation of potential impurities/degradation products at the 0.05-0.1 area% level.