Effects of silicium dioxide oil drug release from suppositories

Silica gel is frequently introduced into lipophilic excipients for suppositories as a viscosity agent, to, prevent drug sedimentation in the melted mass, and to decrease release rate. The effect of silica gel (Aerosil 200) concentration on the availability of some drugs frequently used in suppositories in different unitary doses was studied. When silica gel concentration in the excipient was increased, a decrease in aminophylline and aminophenazone release rate was observed. Paracetamol in small unitary doses has shown a tendency to increase release rate at higher silica gel concentrations. This behavior was even more evident in suppositories containing promethazine hydrochloride, while for those containing benzydamine hydrochloride the increase in release rate with increasing silica gel concentration was evident for all drug doses. However, the behavior was a consequence of the trend of suppository viscosity during drug release. As a consequence of both the drug and silica gel being discharged, the viscosity progressively decreased with an increased silica gel concentration. The effect on drug availability was conditioned by silica gel concentration, as well as the type and dose of the drug, which could act on the shape of the suppository inner structure that is responsible for viscosity and mobility of drug particles.