Pharmacodynamics<unk> acts as an agonist of the<unk> MT1 and MT2 receptors, the biological targets of endogenous<unk>  Endogenous<unk> is normally secreted from the pineal gland of the brain.<unk> is thought to activated<unk> receptors in the suprachiasmatic nucleus of the hypothalamus to regulate the circadian clock and sleep–wake cycles. When used several hours before sleep according to the phase response curve for<unk> in humans, small amounts (0.3 mg) of<unk> shift the circadian clock earlier, thus promoting earlier sleep onset and morning awakening. Pharmacokinetics Absorption The bioavailability of<unk> is between 2.5 and 50%.<unk> is rapidly absorbed and distributed, reaching peak plasma concentrations after 60minutes of administration, and is then eliminated. Usual doses of exogenous<unk> of 1 to 12mg produce<unk> concentrations 10 to 100times higher than endogenous peak levels. Distribution The plasma protein binding of<unk> is approximately 60%. It is mainly bound to albumin, α1-acid glycoprotein, and high-density lipoprotein. The membrane transport proteins that move<unk> across a membrane include, but are not limited to, glucose transporters, including GLUT1, and the proton-driven oligopeptide transporters PEPT1 and PEPT2. Metabolism<unk> is metabolized in the liver by cytochrome P450 enzyme CYP1A2 to 6-hydroxymelatonin. Metabolites are conjugated with sulfuric acid or glucuronic acid for excretion in the urine. Some of the metabolites formed via the reaction of<unk> with a free radical include cyclic 3-hydroxymelatonin, N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), and N1-acetyl-5-methoxykynuramine (AMK). Elimination In humans, 90% of orally administered exogenous<unk> is cleared in a single passage through the liver, a small amount is excreted in urine, and a small amount is found in saliva.<unk> is excreted in the urine 2 to 5% as the unchanged drug.<unk> has an elimination half-life of about 20 to 60 minutes. The half-life of prolonged-release<unk> (Circadin) is 3.5 to 4hours.
Melatonin 
Etoperidone
Sertindole
Tropisetron
Zolpidem
Cilansetron
Chloracyzine
Alosetron