TIME-DOSE-RESPONSE OF TRYPANOSOMA-BRUCEI-BRUCEI TO DIMINAZENE ACETURATE (BERENIL(R)) AND IN-VITRO SIMULATION OF DRUG-CONCENTRATION-TIME PROFILES IN CATTLE PLASMA

Bloodstream form Trypanosoma brucei brucei of axenically growing popul ations were incubated in the presence of 10.0, 1.0 or 0.1 mug/ml dimin azene aceturate (Berenil) at 37-degrees-C for various periods and, sub sequently, either inoculated into mice or further propagated in vitro in drug-free medium. Growth was monitored for 10 days. The ability of trypanosomes of drug-sensitive CP 2137 (clone 1) to grow in vitro was irreversibly damaged after short incubation (< 1 min) with 10.0 mug/ni l or after 15 min with 1.0 mug/ml diminazene aceturate. In contrast, d rug-resistant CP 2469 (clone 1) trypanosomes tolerated incubation with 10 mug/ml of drug for up to 6 h and 1.0 mug/ml of drug for up to 24 h . Differences in drug susceptibility were also detected regarding infe ctivity to mice and changes in trypanosome cell volume. The results de monstrated that less than 1 min exposure to diminazene aceturate at co ncentrations as seen in bovine plasma at the initial peak after dimina zene aceturate treatment is enough to irreversibly damage drug-sensiti ve trypanosomes. However, these concentrations were not sufficient to completely eliminate drug-resistant trypanosomes after exposure for 1- 6 h; trypanosomes continued to grow for 48 h before the majority of th em died and only a few organisms survived to revive the cultures. When drug-sensitive trypanosomes were exposed in vitro for 24 h to diminaz ene aceturate at the level of concentrations found in cattle after tre atment with 3.5 mg/kg, most of the trypanosomes died and none of the s urviving parasites could be propagated in vitro in the absence of drug for more than 2 days. However, a small population of drug-resistant t rypanosomes was not irreversibly damaged and a few surviving trypanoso mes were able to establish growing cultures. The addition of feeder la yer cells did not change the outcome of these experiments.