Intranasal absorption of melatonin in vivo bioavailability study

Abstract

The bioavailability of melatonin in rabbits after nasal administration of two formulations has been studied. In each case, a total amount of 1.5 mg melatonin in 50 μl was administered and compared with 1.5 mg i.v. The test solutions were formulated with 40% polyethylene glycol 300 (PEG 300), one with 1% sodium glycocholate (+GC) and one without (−GC). The bioavailability for +GC was 94% (S.D.±29%, n=4), whereas the bioavailability for −GC was 55% (S.D.±17%, n=6). These results indicate that GC has an enhancer effect ( P<0.05). However, the relatively high bioavailability without GC shows that it might not be necessary to use an enhancer for a clinical relevant formulation. The pharmacokinetics of melatonin could be described by a one-compartment model, and the serum half-life was about 13 min. The absorption rate for both formulations was very fast ( t max=5 min) and C max mean was 493±290 ng/ml ( n=4) and 249±125 ng/ml ( n=6) for +GC and −GC, respectively.