EFFECT OF pH ON THE ANTIFUNGAL ACTIVITY OF UNDECYLENIC ACID AND ITS CALCIUM SALT

Fatty acids exert a fungistatic and fungicidal action on dermatophytes. Optimal activity is associated with low pH, whether for inhibition of growth (Hoffman et al., 1939) or for inhibition of respiration (Chattaway and Thompson, 1956). Various authors (Olson and Macy, 1940; Grunberg, 1947) have suggested that at any pH the antifungal activity is due to the undissociated molecule alone. This theory was critically analyzed by Rahn (1945) and found to be substantially correct for benzoic acid from pH 3.5 to 6.5. A search of the literature revealed that a similar analysis has not been made for a long chain fatty acid. Accordingly, the effect of pH on the antifungal activities of undecylenic acid and its calcium salt was studied, with particular attention paid to the concentration (calculated) of undissociated acid at each pH.