Article

The absolute bioavailability of oral melatonin

Department of Medicine, Bassett Healthcare, Cooperstown, New York 13326, USA.
The Journal of Clinical Pharmacology (Impact Factor: 2.47). 08/2000; 40(7):781-4. DOI: 10.1177/00912700022009422
Source: PubMed

ABSTRACT 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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    • "In humans, orally administered melatonin exhibits extensive first-pass metabolism and its absolute bioavailability is reported to be around 15% with a wide range of variability (Di et al 1997; DeMuro et al 2000). The wide variations in melatonin´s bioavailability is attributed to inter-individual variations in the expression of and activity of CYPA2 and CYP1A (Hartter et al 2001). "
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