Systematic development of a bioanalytical UPLC-MS/MS method for estimation of risperidone and its active metabolite in long-acting microsphere formulation in rat plasma

A systematic approach to develop a UPLC-MS/MS method was applied for quantifying of risperidone (RISP), its active metabolite, 9-hydroxy risperidone (9-OH-RISP) and internal standard (propranolol) in rat plasma. Liquid-liquid extraction was performed using methyl tert-butyl ether for quantification of drug and its active metabolite by MS detection in the positive ion mode. Acquity UPLC system with BEH C18 (2.1 mm × 100 mm, particle size 1.7 μm) column was used along with acetonitrile (0.1% formic acid)–2 mM (milli mole) ammonium acetate in isocratic condition was used as the mobile phase. Detection was performed by multiple reactions monitoring with precursor-to-product ion transitions with m/z 411.2 → 191.0 for RISP, m/z 427.2 → 207.0 for 9-OH-RISP and m/z 260.1 → 116.0 for IS. The method was validated as per the FDA guidance on bioanalytical method validation. Linearity (r² = 0.999) was observed in the drug concentration ranging between 0.1 and 50 ng mL⁻¹, while all other parameters were found to be within the acceptable ranges. Method robustness was optimized by Box-Behnken design to monitor the influential variables to achieve maximal recovery of the analytes in the rat plasma. Pharmacokinetic evaluation of the analytes from long-acting microparticles in rat plasma showed two peaks indicating an initial burst effect within 24 h of administration followed by controlled drug release pattern upto 45 days, while marketed formulation (Risperdal Consta®) showed no plasma concentration during the lag-time of 21 days followed by maximal drug absorption between 28 and 40 days.