Poly(dimethylsiloxane) coatings for controlled drug release. III. Drug release profiles and swelling properties of the free-standing films

Previous reports in this series have described the preparation of stable poly(dimethylsiloxane) (PDMS) latices suitable for spray-coating of drug tablets, as well as the mechanism of associated crosslinking reactions in PDMS emulsions. In the present investigation, in vitro evaluations were performed to study the effects of the amount of channeling agents, the addition of colloidal silica, and the pH of the dissolution media used. The study involved hydrochlorothiazide (as a marker drug) released from compressed tablets, which had been spray coated using PDMS latices with various polyethylene glycol (PEG) loadings as channeling agents. The dissolution results showed that coated tablets containing up to 25% (w/w dps) PEG could have constant release rates. Higher amounts of PEG resulted in nonlinear release patterns. The addition of colloidal silica decreased the rates of drug release. The pH of dissolution media affected the structures of the exposed PDMS films. Swelling tests were carried out to determine water uptake. Scanning electron microscopy and density measurements showed that the films obtained after soaking in higher-pH media were more condensed, with corresponding changes in drug-release rates. (C) 2005 Wiley Periodicals, Inc.