Comparison of the effect of drugs on Babesia in vitro and in vivo.

It was previously shown that Babesia-infected blood maintained in vitro incorporated high levels of 3H hypoxanthine and that the uptake could be suppressed by babesicidal drugs. In the current paper the hypoxanthine pathway was shown to be the most sensitive in testing such drugs for activity in vitro. Other pathways involving orotic acid, glutamine or thymidine were less sensitive. The highest counts were achieved when 3H hypoxanthine was added 1 h after cultures were set up. Drugs which had previously shown activity against Babesia in vitro were added to cultures of B rodhaini and after 24 h incubation parasitised cells were inoculated into groups of mice. Known babesicidal drugs suppressed or delayed infection in mice and 3H hypoxanthine analogues also showed some activity. These analogues, however, showed no therapeutic properties when injected into B rodhaini infected mice.