Abstract
Intending to explore useful ointment bases containing hydroxypropyl cellulose (HPC), an investigation was made on the spreadability, washing-out time and drug release of combined mixtures of HPC with aqueous glycerine (Aq. G1), propylene glycol (PG) and polyethylene glycol (PEG). The decrease of the spreadability due to the increase of concentration of HPC was remarkable in the low concentration, declining above 10% (w/v) in HPC/PG and above 14% (w/v) in HPC/PEG. HPC/PEG containing above 12% (w/v) lost the fluidity to take a gel-like state and this gel-like mixture indicated a typical thixotropic phenomenon. The washing-out time increased with the concentration of HPC, and it seemed to be related to the increase of viscosity. With the addition of 30% of zinc oxide as an insoluble drug, the decrease of spreadability was 23% at the largest, which was observed for HPC/Aq. G1. The spread radius at 2 min on the measurement for the sample of HPC/PEG (10 : 100, w/v) after heating at 150° for 1 hr was 54% larger than that of the intact one, indicating the structure relating to the thixotropy of the mixture might be crushed by heating. The drug release from each mixture decreased with the increase of concentration of HPC. HPC/PEG showed the fastest drug release at the given spreadability below 4.1 cm. As a result, it was shown that HPC would provide a promising material as bases for ointments and other semisolid preparations combining properly with Aq. G1, PG and PEG.
