Pharmacokinetics of Repeated Melatonin Drug Administrations Prior to and After Surgery.

BACKGROUND: Recent clinical studies have documented the analgesic, anti-inflammatory, antioxidative and anxiolytic effects of exogenous melatonin. The pharmacokinetic properties of melatonin have primarily been investigated in experimental studies. OBJECTIVE: The aim of this study was to estimate the pharmacokinetics of melatonin in patients undergoing surgery and general anesthesia. METHODS: The study was designed as a prospective, two-phase cohort study. Patients were candidates for subpectoral breast augmentation surgery, and surgical procedures were performed by a single surgeon. The perioperative treatment protocol was standardized between patients. During the study, each patient received two separate oral administrations of melatonin 10 mg. Melatonin was administered 60 min before surgery, and at 9:00 p.m. the evening after surgery. The pharmacokinetic variables absorption half-life (t ½ absorption), time to maximal plasma concentration (T max), maximal plasma concentration (C max), elimination half-life (t ½ elimination), and area under the melatonin plasma concentration-time curve from time zero to infinity (AUC ∞) were estimated for both study phases. RESULTS: Median (interquartile range) values of t ½ absorption and T max were significantly increased during the postoperative phase [10.8 (6.9-15.1) min; 90.0 (48.8-120.0) min] compared with perioperatively [9.5 (6.3-16.5) min; 30.0 (15.0-30.0) min] (p = 0.034; p = 0.002), respectively. C max values were significantly higher during surgery [5497.5 (2077.1-13,233.8) pg/ml] compared with postoperative values [2340.5 (1672.4-8871.4) pg/ml] (p = 0.005). Correspondingly, t ½ elimination was significantly extended during the postoperative phase [103.5 (57.8-237.8) min] compared with the perioperative phase [60.5 (47.8-83.6) min] (p = 0.015). AUC ∞ did not differ between the study phases (p > 0.05). CONCLUSIONS: These preliminary results indicate that postoperative melatonin dose should be augmented compared with preoperative administration if corresponding melatonin plasma levels are intended. Furthermore, postoperative administration times should be advanced compared with preoperative administration.

Clinical pharmacokinetics of melatonin: a systematic review.

PURPOSE: The aim of the review was to provide an overview of studies investigating the pharmacokinetics of exogenous melatonin in humans and if possible, to provide recommendations for clinical use. METHODS: The review was conducted in accordance to PRISMA guidelines. A systematic literature search was performed in PubMed and Embase databases. The pharmacokinetic variables included maximal plasma/serum concentration (Cmax), time to maximal plasma/serum concentration (Tmax), elimination half-life (T1/2), area-under-the-curve plasma/serum concentrations (AUC), clearance (Cl), volume of distribution (VD), and bioavailability. RESULTS: The literature search identified 392 records. Twenty-two studies were included in the review. Melatonin dosages varied between 0.3 and 100 mg and were administered either orally or intravenously. Cmax ranged from 72.1 (10 ml/h; 0.02 mg, IV) to 101,163 pg/ml (100 mg, oral). Tmax ranged between 15 (2 mg) and 210 min (10 mg). T1/2 ranged from 28 (0.005 mg, IV) to 126 min (4 mg, oral), whereas AUC ranged between 5400 (0.005 mg, IV) and 6.56 × 10(10) pg/ml × min (1 mg, oral). Cl ranged from 0.97 (0.005 mg, IV) to 132.50 L/min (6 mg, oral), whereas VD ranged between 35 (0.005 mg, IV) and 1602 L (4 mg, oral). Bioavailability of oral melatonin ranged from 9 to 33%. Pharmacokinetics was affected by age, caffeine, smoking, oral contraceptives, feeding status, and fluvoxamine. Critically ill patients displayed accelerated absorption and compromised elimination. CONCLUSIONS: Despite methodological differences between the included studies, Tmax was approximately 50 min following oral immediate-release formulations of melatonin. T1/2 was 45 min in both administration routes. Cmax, AUC, Cl, and VD varied extensively between studies. Bioavailability of oral melatonin was approximately 15%.