Stability behaviour of antiretroviral drugs and their combinations. 2: Characterization of interaction products of lamivudine and tenofovir disoproxil fumarate by mass and NMR spectrometry.

This study focused on drug-drug interaction behaviour among lamivudine (3TC) and tenofovir disoproxil fumarate (TDF), the two anti-retroviral drugs. Apart from pre-known degradation products of individual drugs, a total of twelve interaction products were detected by high performance liquid chromatography (HPLC) using a C18 column as the stationary phase, and methanol and ammonium formate in gradient mode as the mobile phase. The same HPLC method was employed for liquid chromatography-high resolution mass spectrometry (LC-HRMS) and liquid chromatography-multi stage mass spectrometry (LC-MS(n)). For the characterization of interaction products, stability samples were subjected to LC-HRMS, LC-MS(n) and online hydrogen/deuterium exchange studies. Two isomeric interaction products were isolated and subjected to 1D and 2D nuclear magnetic resonance (NMR) studies. The collated information was utilized for the characterization of all twelve interaction products of the two drugs. Pathway of their formation was also outlined.