Heterogeneity in the responses of clones of Giardia intestinalis to anti-giardial drugs.

Clones of two stocks of Giardia intestinalis have been tested by the [3H]thymidine uptake assay to determine their sensitivity to metronidazole, tinidazole, furazolidone and quinacrine. Each stock was not homogeneous with respect to drug sensitivity but was composed of different populations of organisms. Doubling times of lines derived from clones of a stock did not vary significantly. These findings may, in part, account for treatment failures in human giardiasis patients.