A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the simultaneous quantification of apomorphine and its metabolites apomorphine sulfate and norapomorphine in human plasma for supporting clinical development of a novel apomorphine sublingual thin film (APL) for the treatment of Parkinson's disease. Analytes and internal standards (IS) were extracted from human plasma by Oasis HLB SPE cartridge, followed by a reversed phase LC-MS/MS analysis using multiple reaction monitoring (MRM) in positive mode (m/z 268 → 237 for apomorphine, 348 → 237 for apomorphine sulfate, and 348 → 237 for norapomorphine). Stable isotope-labeled compounds were used as IS for respective analytes. The validated curve ranges were 0.02-20 ng/mL, 10-1000 ng/mL, and 0.5-20 ng/mL for apomorphine, apomorphine sulfate and norapomorphine, respectively. Extraction recoveries were found to be 73.4 % (apomorphine), 81.1 % (apomorphine sulfate), and 58.6 % (norapomorphine). Established long-term plasma frozen storage stabilities were 504 days at -20 °C and276 days at -60 °C, respectively. The method has been successfully used for analyzing pharmacokinetics (PK) samples collected from a comparative bioavailability study of APL and the marketed apomorphine subcutaneous (s.c.) product Apo-go®. The results demonstrated that the 15-mg APL film administrated via sublingual produced comparable PK characteristics of apomorphine when compared to the commercial product Apo-go (2-mg) via s.c. administration, hence establishing the dose regimen for this sublingual formulation. It was also noticed that the sublingual 15-mg APL film produced a significantly higher apomorphine sulfate metabolite level than the 2-mg s.c. Apo-go, and both treatments yielded a negligible level of norapomorphine metabolite in humans.
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