Characterization and in vitro release of praziquantel from poly(epsilon-caprolactone) implants

Poly(epsilon-caprolactone) (PCL) implants containing praziquantel (PZQ), a broad-spectrum antiparasite drug, are fabricated by injection molding and characterized in terms of content uniformity, morphology, drug physical state and stability. In vitro drug release from the implants is also studied. It is found that drug is dispersed uniformly in all implants and keeps stable over 365 days at 4 degrees C/60% RH. X-ray diffraction analysis reveals that PZQ exists primarily in its crystalline state in implants with high drug contents (50% and 25%). All implants exhibit similar release behaviors and about 70% of the drug is released after 365 days. The cross-sections of all implants present two distinct zones (i.e. peripheral white zone and inner pink zone) and the boundary between the two zones changes as time progresses. Drug content in the white zone is very low (less than 1%), but drug content in the pink zone is almost the same as the predefined value. Porous structures in the white zone but dense structures in the pink zone are observed by SEM. Obvious PCL degradation occurs till up to 365 days. These results show that the release process of PZQ is a gradual diffusion from the exterior to the interior of the implants.