Ineffectiveness of Certain Pentavalent Arsenicals Used Orally in T. hippicum Infected Guinea Pigs

Abstract

Kolmer 1 has reported that “stovarsol and treparsol in doses of approximately 0.030 to 0.040 gm. per kilo of weight by oral administration for 3 to 10 days were effective in preventing trypanosomiasis of rats infected with T. equiperdium. Atoxyl was slightly more effective, as doses of 0.020 to 0.030 gm. per kilo per day (orally)…. for 5 to 10 days prevented infection.” Tryparsa-mide and “Bayer 205” or “Germanin” were ineffective when given orally to infected animals. He further states that when treatment was started 24 hours after infection the arsenicals were more active than when given before or at the time the infection was induced. Cooper 2 originally demonstrated this phenomenon using tryparsa-mide, etharsanol and “arsenoxide”.

The treatment of equine trypanosomiasis (T. hippicum) has been unsatisfactory with the common trypanocides because horses require large amounts of expensive drugs given intravenously. Dr. Herbert Clark 3 of Panama has been partially successful with approximately 5 times the human dose of tryparsamide or “Bayer 205” combined with tartar emetic, given at weekly intervals over relatively long periods. Certain disadvantages are: first, that the cost of medication may exceed the value of the treated animal, secondly, that embolic phenomena occur with intravenous administration, thirdly, that neither prophylactic therapy nor treatment of infected animals is always successful. A more satisfactory form of therapy is needed, that is, a cheap drug that can be given by mouth without toxicity in prophylactic or therapeutic doses. Kolmer's report suggested the possibility of a successful approach to the problem from the standpoint of oral effectiveness with certain arsenical trypanocides.

Guinea pigs infected with the Panamanian strain of T. hippicum were treated with atoxyl, acetarsone (“stovarsol'), and carbarsone given orally. Standard intraperitoneal injections were made into normal healthy guinea pigs using 0.3 cc. of infected guinea pig blood with an equivalent amount of sterile physiological saline.