[Contributions to the liberation of drugs from suspension ointments. Part 12: On the suitability of some synthetic hydrophobic membranes for liberation studies (author's transl)].

The release rates determined for various salicylic acid and prednisolone ointments on using different membranes in the in vitro model according to Horsch and Kögel [20] were compared with one another in regard to possible membrane-specific differences in liberation kinetics and in validity. The results obtained with salicylic acid ointments by the lipophil collodion-lipid membranes and silicone membranes developed by Fürst and coworkers [14] were comparable with those yielded by the hydrophilic cellulose membrane: release rates of comparable order of magnitude; same order of ranking of the bases used; plots of the cumulated percentages of release against the root of time providing no evidence of differences in kinetics. In contrast, the permeability of a further hydrophobic membranes (silicone, polyester) was markedly lower. As to the prednisolone ointments, the collodion-lipid membranes yielded comparable release rates and orders of ranking when the drug was incorporated into hydrophilic bases, whereas the silicone membrane was considerably inferior in permeability.