Antigiardial activity of the bile salt-like antibiotic sodium fusidate

Possible antigiardial activity of the bile salt-like antibiotic, sodium fusidate has been investigated during 24 h liquid culture of Giardia lamblia trophozoites and in 4 h microassays for parasite motility inhibition and viability. Sodium fusidate inhibited Giardia growth (ED50 0.2 mM; MIC 0.3 mM) but was considerably less potent than metronidazole (ED50 0.002 mM; MIC 0.05 mM). Sodium fusidate and metronidazole were active inhibitors of parasite motility (ED50 0.9 and 0.3 mM respectively) but were largely without effect in the 4 h viability assay. Sodium fusidate was active at concentrations well below its critical micellar concentration (2.7 mM) suggesting that its effect was not merely related to its membranolytic detergent properties. Its taurine and glycine conjugates were markedly less potent and paradoxically stimulated growth at low concentration. The studies suggest that sodium fusidate does have antigiardial activity and in view of its relative freedom from teratogenic and other toxic effects may be useful in pregnancy when other antigiardial agents are contra-indicated or as an adjunct in combination therapy when other single agents have failed to eradicate infection.