Analysis of methylphenidate and its metabolite ritalinic acid in monkey plasma by liquid chromatography/electrospray ionization mass spectrometry

Methylphenidate (MP, Ritalin(R)) is a psychotropic drug widely prescribed t o children for treating the symptoms of attention deficit disorder with and without hyperactivity, Because little information exists about the effects of chronic MP administration on cognitive function in children, measures o f behavior changes in non-human primates are important surrogates. An essen tial component of such studies is the determination of MP plasma levels und er chronic and acute dosing conditions, An analytical method was developed that provided sufficient sensitivity to measure low levels of the active pa rent drug (lower limit of quantitation = 0.25 ng/mL) and the inactive metab olite, ritalinic acid (RA), in monkey plasma as well as the ability to conv eniently analyze large numbers of samples. The method uses a polymeric reve rsed-phase sorbent for solid phase extraction, an efficient reverse-phase h igh performance liquid chromatography (HPLC) separation, deuterated interna l standards for isotope dilution quantification of MP and RA, and detection by sensitive electrospray ionization mass spectrometry (ES-MS) with a sing le quadrupole instrument. The method responses are linear over the range of plasma concentrations of MP and RA observed in monkeys, gives respective a nalyte recoveries of 75 and 60% with reasonable precision and accuracy, and demonstrates robust MS performance for rapid determination of MP/RA plasma levels, The average peak MP concentration (ca. 16 ng/mL) and half-lives fo r MP and RA elimination in monkeys (1.79 and 2.31 h, respectively) were not significantly different under acute vs. chronic dosing conditions and were comparable to values previously reported from human studies. Copyright (C) 2000 John Wiley & Sons, Ltd.