Swellable elementary osmotic pump (SEOP): an effective device for delivery of poorly water-soluble drugs

A new type of elementary osmotic pump (EOP) tablet for efficient delivery of poorly water-soluble/practically insoluble drugs has been designed. Drug release from the system, called swellable elementary osmotic pump (SEOP), is through a delivery orifice in the form of a very fine dispersion ready for dissolution and absorption. SEOP tablets were prepared by compressing the mixture of micronized drug and excipients into convex tablets. Factors affecting the release of drug from the SEOP tablets containing a poorly water-soluble drug, indomethacin, have been explored. The release behaviour of indomethacin from different formulations of this dosage form was studied at pH 6.8 for a period of 24 h. The formulations were compared based on four comparative parameters, namely, D24h (total release after 24 h), tL (lag time), RSQzero (R square of zero order equation) and D%zero (percentage deviation from zero order kinetics). The drug release profile from osmotic devices showed that the type of polymer in the core formulation can markedly affect the drug release. The results showed that concentration of wetting agent in the core formulation was a very important parameter in D24h and release pattern of indomethacin from SEOP system. Increasing the amount of wetting agent to an optimum level (60 mg) significantly increased D24h and improved zero order release pattern of indomethacin. Increasing concentration of caster oil (hydrophobic) in the semipermeable membrane of the device or hydrophilic plasticizer (glycerin) in coating formulation markedly increased tL and decreased D24h. The results also demonstrated that aperture size is a critical parameter and should be optimized for each SEOP system. Optimum aperture diameter for the formulations studied here was determined to be 650 µm for zero order release pattern. tL and D%zero were dramatically decreased whereas D24h and RSQzero increased with increasing the aperture size to optimum level. This study also revealed that optimization of semipermeable membrane thickness is very important for approaching zero order kinetics. © 2007 Elsevier B.V. All rights reserved.