In vitro drug susceptibility of 29 isolates of Giardia duodenalis from humans as assessed by an adhesion assay.

Twelve isolates of Giardia duodenalis from Caucasian hosts in the Perth metropolitan area, along with 16 isolates from Aborigines in the north of Western Australia and the reference isolate P1C10 were examined for their in vitro drug sensitivity. Dose-response curves were constructed for each isolate for metronidazole, the most common clinically used antigiardial agent, as well as for the benzimidazole compound albendazole. Less than a 9-fold variation was found in the susceptibility of the isolates to albendazole, while for metronidazole there was well over a 16,000-fold variation between the same group of isolates. In addition, it was found that isolates of Giardia obtained from Aboriginal hosts were significantly less sensitive to albendazole than those obtained from Caucasians. The results of this study have important implications for the continued use of metronidazole and the potential use of albendazole for the treatment of giardiasis.