Drug resistance in Sudanese Trypanosoma evansi

The drug sensitivities of 16 Trypanosoma evansi isolates from Sudan were examined using two different in vitro assays and rodent models. IC50 values (concentration which inhibited incorporation of 3H-hypoxanthine by 50%) obtained in a 40 h assay indicate that most of the isolates were resistant to suramin, a drug which has not been used in Sudan since 1975. Sensitivities for suramin in a 10-day-in vitro assay varied within a 124-fold range. The in vitro results were confirmed by infection/treatment experiments in mice. Sensitivities in vitro for quinapyramine varied within a 166-fold range. In mice, the least sensitive isolates were not cured with dosages up to 10 mg/kg quinapyramine. Based on in vitro results, all isolates appeared to be susceptible to isometamidium.