Bioavailability of Melatonin after Administration of an Oral Prolonged-Release Tablet and an Immediate-Release Sublingual Spray in Healthy Male Volunteers

Abstract Background The benefit of exogenous melatonin is based on its bioavailability, which depends on the galenic form, the route of administration, the dosage, and the individual absorption and rate of hepatic metabolism. Objective The objective of this study is to investigate the bioavailability of melatonin after administration of an oral prolonged-release tablet (PR form) and an immediate-release sublingual spray (IR form). The main metabolite of melatonin, 6-sulfatoxymelatonin (6-SMT), was also measured, which has not been done in previous studies. Its determination is important as an index of the hepatic transformation of melatonin. Methods In this single-center, open-label, randomized, crossover study, 14 healthy male volunteers received one tablet of the PR form (1.9 mg melatonin) or two sprays of the IR form (1 mg melatonin) during two visits separated by a washout period. Blood samples were collected over 7 and 9 h for the IR and PR form, respectively, to determine the main pharmacokinetic parameters. Results The observed kinetics were consistent with those expected for immediate and prolonged-release forms. Pulverization of the spray resulted in an early, high plasma melatonin peak (C max: 2332 ± 950 pg/mL; T max: 23.3 ± 6.5 min), whereas tablet intake produced a lower peak (C max: 1151 ± 565 pg/mL; T max: 64.2 ± 44.2 min; p