Key result
Oral melatonin yields poor absolute bioavailability of ~15% compared to IV administration.
Why the study?
The absolute bioavailability of oral melatonin tablets in healthy volunteers was not well characterized.
RCT (n=12)
crossover
Oral melatonin tablets in dosages of 2 and 4 mg show poor absolute bioavailability of approximately 15%, likely due to poor oral absorption or large first-pass metabolism.
Melatonin oral dosing may require adjustment or alternative routes; extends pharmacokinetic data to inform formulation and trial design.
The absolute bioavailability of oral melatonin tablets was studied in 12 normal healthy volunteers. Subjects were administered, in a randomized crossover fashion, melatonin 2 mg intravenously and 2 and 4 mg orally. Blood was sampled over approximately eight (estimated) half-lives. Both the 2 and the 4 mg oral dosages showed an absolute bioavailability of approximately 15%. No difference in serum half-life was seen in any of the study phases. Oral melatonin tablets in dosages of 2 and 4 mg show poor absolute bioavailability, either due to poor oral absorption, large first-pass metabolism, or a combination of both. Further studies examining larger doses, in an attempt to saturate first-pass metabolism if it occurs, may be warranted.
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DeMuro et al. (2000) conducted an RCT in healthy volunteers (n=12). Oral melatonin vs. Intravenous melatonin 2 mg was evaluated on absolute bioavailability. Oral melatonin tablets in dosages of 2 and 4 mg demonstrated poor absolute bioavailability of approximately 15% compared to intravenous administration.
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