Selective Inhibition of Sulfonamide Drugs by Various Media

Sulfathiazole and sulfadiazine are inhibited to varying degrees in different media. In blood broth sulfadiazine is selectively inhibited to a greater degree than sulfathiazole. In human serum sulfathiazole is inhibited to a greater degree than it is in blood broth, in human plasma, in defibrinated blood or in horse serum, while sulfadiazine is inhibited to about the same extent in these media. In liver infusion medium sulfadiazine and sulfathiazole are equally effective in a concentration of 5 mg % but sulfathiazole is more effective in lower concentrations. The possible error of attempting to compare therapeutic efficacy of different sulfonamides on the basis of the results of in vitro tests is discussed and the importance of the proper selection of media for the performance of in vitro tests of sulfonamide drugs is emphasized.