An Account of Modified Release of Melatonin from Compression-coated, Uncoated and Bilayer Tablets

Modified release formulations offer several advantages over conventional systems used in therapeutics. The aim of this work was to extend our previous studies on the chronobiotic hormone melatonin controlled release, by comparing its release from uncoated, compression-coated and bilayer tablets. Each tablet was comprised of melatonin and combinations of the following excipients: ethylcellulose, polyvinylpyrrolidone (PVP, MW:10.000), dextran, low viscosity sodium alginate, Avicel PH 102, lactose monohydrate, iron oxide pigment red 30 and magnesium stearate. The compression-coated tablets consist of the same drug and inner excipients core, but different outer coating shells. As for the bilayer tablets, they incorporate an immediate release layer and a sustained release layer. The dissolution experiments were carried out in a USP XXIII dissolution apparatus for ten hours (the first three hours at pH 1.2 and the rest seven at pH 7.4). The results obtained reveal that the initial release of melatonin is slower from coated tablets than from the respective uncoated. The use of lactose in the outer coating shell, instead of PVP, results in a lower release in the pH 1.2 medium. In the medium with pH 7.4, lactose leads to a faster release than PVP. The increase of dextran concentration in the outer coating shell of the coated tablets delays the drug release at both pHs. In uncoated tablets, most of the formulations show similar release profiles, although the presence of PVP seems to delay the drug release. The release of melatonin from bilayer tablets, is initially faster than from both coated and uncoated tablets. The present study demonstrates that the assembly of tablets, with and without coatings, results to different controlled release behaviour of the chronobiotic hormone melatonin.