An investigation was conducted on the therapeutic and prophylactic activity of
isometamidium chloride (SamorinR) in Boran (Bos indicus) cattle against a Trypanosoma congolense clone, IL 3270. This clone was derived, without
drug selection, from a stock originally isolated in Burkina Faso and has previously been shown to be resistant to
isometamidium in both cattle and mice using an
infection and treatment regimen. A group of 5 cattle were treated intramuscularly with 1.0 mg kg-1
isometamidium chloride and 28 days later challenged with Glossina morsitans centralis infected with T. congolense IL 3270. All 5 cattle and 17 untreated cattle challenged on the same day became parasitaemic by day 16 post challenge, indicating that prophylaxis did not extend to 28 days post treatment. The cattle were then treated with
isometamidium chloride at one of the following doses and by different routes of administration; 1.0 or 2.0 mg kg-1 intramuscularly, 0.25, 0.5, 0.75 or 1.0 mg kg-1 intravenously.
Infections relapsed in all cattle at an interval of 12-21 days following treatment, with the exception of those treated with 2.0 mg kg-1 intramuscularly in which the development of relapse
infections was delayed. Similar studies were also conducted with a highly sensitive clone of T. congolense, IL 1180.
Infections in cattle with this clone were eliminated by intravenous treatment with 0.25 mg kg-1
isometamidium chloride or intramuscular treatment with 0.5 mg kg-1
isometamidium chloride. Thus, although
intravenous administration of
isometamidium eliminated a fully sensitive
infection, treatment by this route appeared not to enhance the therapeutic efficacy of the
drug in the treatment of a T. congolense clone which expresses a high level of resistance.