The effect of pH and of temperature on the stability and bioactivity of nystatin and amphotericin B

Abstract In the presence of phosphate-citrate buffers, nystatin and amphotericin B are optimally stable between pH 5 and 7. Loss of biological activity followed first-order kinetics, except under acid conditions. Apparent energies, enthalpies, free energies and entropies of activation of the two antibiotics have been calculated at pH 7, and the two sets of figures are similar. Variation in pH between 5 and 8 appeared to have little effect of the activity of amphotericin B against Candida albicans, while nystatin was more active at pH values between 6 and 8. Nystatin was more active at lower incubation temperatures (30-25°), while amphotericin B appeared to be more active at 41°.