Hot-melt extruded ethylcellulose cylinders containing a HPMC–Gelucire® core for sustained drug delivery

The objective of the study was to develop a sustained release system consisting of a hot-melt extruded ethylcellulose pipe surrounding a drug-containing hydroxypropyl methylcellulose (HPMC)–Gelucire® 44/14 core, yielding a monolithic matrix system applicable in the domain of sustained drug release. The influence of HPMC substitution type and viscosity grade was investigated through dissolution testing and erosion studies. All sustained release systems showed a nearly constant drug release profile with only 40% of the drug released after 24 h. To achieve complete drug release after 24 h, the core formulation and the dimensions of the hollow pipe were modified. Changing the composition of the core did not result in the intended zero-order drug release. Shortening the length of the ethylcellulose cylinder accelerated drug release, while modifying the diameter did not affect the drug release rate. The drug dissolution profile and the release mechanism were independent of drug solubility. Increasing the drug loading caused a small increase of the drug release rate, but did not alter the release mechanism.