COMPARATIVE-EVALUATION OF THE PROPHYLACTIC EFFECT OF SLOW-RELEASE DEVICES CONTAINING HOMIDIUM BROMIDE AND ISOMETAMIDIUM ON TRYPANOSOMA-CONGOLENSE IN RABBITS

Two consecutive experiments were carried out to evaluate the prophylac tic effect of biodegradable slow release devices (SRD), containing eit her isometamidium or homidium bromide. Rabbits subcutaneously implante d with SRD, were challenged with different Trypanosoma congolense stoc ks at regular intervals between 1 and 6.5 months after treatment. In a first experiment the efficacy of two types of isometamidium-SRD (poly (D,L-lactide) and poly(D,L-lactide-co-glycolide)) was compared with th e classical intramuscular (i.m.) injection of the drug. Since the form er polymer gave an average protection period, which was much longer th an the other isometamidium formulation, a second experiment was carrie d out to evaluate the prophylactic effect of poly(D,L-lactide) SRD, co ntaining either isometamidium or homidium bromide, with that of the i. m. injections of the same drugs at a dose of 1 mg kg(-1). The average protection period of the homidium bromide SRD was significantly longer than that of the i.m. injected drug(112 vs. 49 days). No significant difference was obtained, however, when isometamidium was administered either as a SRD or as an i.m. injection. The average protection period s were, respectively, 106 +/- 37 days and 84 +/- 18 days, When breakth rough isolates derived from SRD-treated animals were compared with the original stocks of T. congolense, the former showed some loss of sens itivity to homidium bromide. No difference in sensitivity was observed , however, for isometamidium.