Preparation and in vitro/in vivo evaluation of sustained-release venlafaxine hydrochloride pellets

The objective of this study was to prepare different venlafaxine hydrochloride sustained-release products and to elucidate the influence of composition of the coating film on the in vitro drug release profiles and in vivo pharmacokinetics. Pellets were prepared by a standardized process of extrusion/spheronization. A selected fraction size (0.8-1.0 mm diameter) of pellets of each formulation was coated with Eudragit NE30D or ethylcellulose (10 cps). Many efforts have been made to tailor drug release rate by choosing different coating materials, different percent of pore forming components and coating weight variation to achieve a desired sustained-release effect. The dissolution studies were performed and data were analyzed in terms of cumulative release as a function of time. The influence on the release of venlafaxine from sustained-release capsules was observed in dissolution media of different pH and gradient pH. Scanning electron microscope (SEM) micrographs revealed morphological changes of the pellet coating surface which were related to in vitro drug release profiles. The relative bioavailability for Formulation 1 and Formulation 2 was evaluated in six healthy beagle dogs after oral administration in a fast state using sustained-release capsules (Effexor XR) as a reference. The results suggested that Formulation 1 and Formulation 2 both had better bioavailability compared with Effexor XR. It could be found that there existed quite difference in the in vivo release and oral absorption performances, despite the similar in vitro drug release behavior for the two formulations. It might be attributable to complex in vivo environment and then variation in the release behavior. Thus differences in the film micro-structure and surface roughness caused by aqueous dispersion and organic solvent coating techniques strongly influence the in vivo release and oral absorption performances.