RP-HPLC-Based Stability-Indicating Analytical Method for Concurrent Determination of Finasteride and Tadalafil: Development and Validation

A stability-indicating RP-HPLC method was developed for the simultaneous estimation of Finasteride and Tadalafil using a Symmetry C18 column and an Acetonitrile:0.1% TEA buffer (pH 2.5, 20:80) mobile phase. Detection at 257 nm, flow rate of 1.0 mL/min, and 6-minute runtime ensured effective separation. The method showed linearity from 12.5–75 µg/mL with R² > 0.999, precision with %RSD < 2%, and LOD/LOQ values of 0.60 µg/mL and 2.00 µg/mL. Assay results for the marketed formulation (ENTADFI) showed 100.0% and 100.2% for Finasteride and Tadalafil, respectively. Forced degradation studies confirmed that Finasteride and Tadalafil were susceptible to degradation under acid, alkali, and oxidative conditions, with maximum degradation observed under acidic (14.0%) and oxidative (14.7%) stress for Finasteride, and under alkali (10.8%) and reduction (14.6%) for Tadalafil. Minimal degradation was seen under thermal and hydrolytic conditions