Anti-human immunodeficiency virus drugs are ineffective against Pneumocystis carinii in vitro and in vivo

Human immunodeficiency virus (HIV) protease inhibitors (PIs) recently have been reported to be active against Pneumocystis carinii in cell culture. Tw elve anti-HIV drugs were analyzed for their effects against rat P. carinii by an ATP cytotoxicity assay. Indinavir and saquinavir exhibited slight ant i-P. carinii activity at concentrations above those that can be clinically achieved in serum; other PIs and nucleoside and nonnucleoside reverse-trans criptase inhibitors were inactive against the organism. Anti-HIV drugs, alo ne or in combination, did not materially reduce the organism count in the t reatment of P. carinii pneumonia in immunosuppressed mice. Thus, anti-HIV d rugs have little or no activity against P. carinii in these in vitro and in vivo systems. Caution should be used when interpreting reports of the susc eptibility of P. carinii to anti-HIV drugs on the basis of in vitro testing only.