Dapsone in low doses prevents Pneumocystis carinii pneumonia in the rat model

Less toxic drugs are needed for the prophylaxis and treatment of Pneumocystis carinii pneumonia (PCP) in patients with AIDS. Rats immunosuppressed with cortisone were given dapsone, chlorproguanil (CPG) and chlorcycloguanil (CCG), alone or in combination, in the diet and the P. carinii attack rate was compared with that of untreated controls. Dapsone alone at doses of 25 and 5 mg/kg/day was 100% effective in preventing PCP. The efficacy of CPG and CCG, however, could not be properly assessed because of the lack of acceptance of the diet by the animals. Even so, as a result of the findings with dapsone in this study, and because of its pharmacokinetics and minimum inhibitory concentration for P. carinii in vitro, a clinical trial of reduced dosage of dapsone given prophylactically to human beings is suggested. Such a trial may show a decrease in the toxicity of the drug that usually accompanies its long-term administration but retention of its efficacy.