The absolute bioavailability of oral melatonin.
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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ABSTRACT: From a physiological perspective the sleep-wake cycle can be envisioned as a sequence of three physiological states (wakefulness, non-rapid eye movement, NREM, sleep and REM sleep) which are defined by a particular neuroendocrine-immune profile regulating the metabolic balance, body weight and inflammatory responses. Sleep deprivation and circadian disruption in contemporary "24/7 Society" lead to the predominance of pro-orexic and proinflammatory mechanisms that contribute to a pandemic metabolic syndrome (MS) including obesity, diabetes and atherosclerotic disease. Thus, a successful management of MS may require a drug that besides antagonizing the trigger factors of MS could also correct a disturbed sleep-wake rhythm. This review deals with the analysis of the therapeutic validity of melatonin in MS. Melatonin is an effective chronobiotic agent changing the phase and amplitude of the sleep/wake rhythm and having cytoprotective and immunomodulatory properties useful to prevent a number of MS sequels. Several studies support that melatonin can prevent hyperadiposity in animal models of obesity. Melatonin at a low dose (2-5 mg/day) has been used for improving sleep in patients with insomnia and circadian rhythm sleep disorders. More recently, attention has been focused on the development of potent melatonin analogs with prolonged effects (ramelteon, agomelatine, tasimelteon, TK 301). In clinical trials these analogs were employed in doses considerably higher than those usually employed for melatonin. In view that the relative potencies of the analogs are higher than that of the natural compound, clinical trials employing melatonin doses in the range of 50-100 mg/day are needed to assess its therapeutic value in MS.Neuro endocrinology letters 09/2011; 32(5):588-606. · 0.94 Impact Factor
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ABSTRACT: This study tested the efficacy of timed oral administration of melatonin as an alternative both to invasive methods (daily injections, timed infusions) and to untimed oral administration in Siberian hamsters (Phodopus sungorus), an important model for the study of photoperiodism. Hamsters readily consumed a small piece of melatonin-treated apple immediately when presented and circulating melatonin was rapidly elevated with a half-life of approximately 3.5 h. Melatonin-treated apple was fed to hamsters for 3 weeks at 2 h before lights off to extend the duration of the nighttime rise in endogenous melatonin. Melatonin treatment induced testicular regression and elevated serum cortisol, effects comparable to those in hamsters exposed to short days. These findings support the hypothesis that timed oral administration of melatonin can mimic the effects of short days and provide a method by which melatonin can be delivered without the potentially confounding effects of handling and injection stress.General and Comparative Endocrinology 06/2006; 146(3):211-6. DOI:10.1016/j.ygcen.2005.11.004 · 2.67 Impact Factor
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ABSTRACT: For a more effective transdermal delivery of melatonin (MT), the effects of vehicles and enhancers on its skin permeation and lag time were evaluated. Skin permeation study was conducted in Franz diffusion cells using excised hairless mouse skins. MT was analyzed by HPLC. As vehicles, ethanol (EtOH), polyethylene glycol 400 (PEG), or propylene glycol (PG) was used alone or mixed with a phosphate buffer. Binary vehicles (EtOH/buffer, PEG/buffer, PG/buffer) showed different effects on the skin permeation of MT and its lag time. Compared with the buffer alone, the PEG/buffer shortened the lag time of MT but reduced its skin permeation. EtOH/buffer significantly increased the flux of MT but prolonged the lag time with the content of EtOH. PG/buffer did not affect the lag time but slightly increased the skin permeation of MT at the higher content of PG (> or =80%). These results indicate that the composition of vehicles exerts significant influence but it per se might have limitation in modulating the transdermal delivery of MT. Next, one tested whether fatty acids could more effectively enhance the skin permeation of MT and shorten its lag time. Given the influence of vehicles on both permeation and lag time, PG was used as a vehicle for fatty acids. The permeation-enhancing effects of saturated fatty acids increased in the following order: C10>C12>C14>C16>C18. The saturated fatty acid, however, did not significantly shorten the lag time regardless of the carbon chain length. Meanwhile, similar to saturated lauric acid (C12), unsaturated oleic acid (C18) dramatically enhanced the skin permeability coefficient of MT more than 950-fold over the effect of PG alone. Moreover, oleic acid showed the shortest lag time (2.1 h). The results suggest that oleic acid in a suitable vehicle could more effectively enhance the skin permeation of MT and shorten its lag time than did the vehicles of various compositions.International Journal of Pharmaceutics 01/2001; 212(1):63-71. DOI:10.1016/S0378-5173(00)00598-6 · 3.79 Impact Factor