Quinupristin-dalfopristin is active against Toxoplasma gondii

Synercid and each of its components (quinupristin and dalfopristin) were ex amined for their activities against Toxoplasma gondii. In vitro, intracellu lar replication of tachyzoites was inhibited by synercid and each of its tw o components. The 50% inhibitory concentrations of synercid, quinupristin, and dalfopristin were 1.6, 2.7, and 6.3 mu g/ml, respectively. Thus, synerc id was markedly more active than its components. Treatment of acutely infec ted mice with 100 or 200 mg of synercid per kg of body weight per day admin istered intraperitoneally for 10 days resulted in survival of 50% (P = 0.00 02) and 100% (P < 0.0001) of infected mice, respectively, whereas all contr ol mice died by day 18. In contrast, treatment with 200 mg of either quinup ristin and dalfopristin per kg per day alone resulted in only 20% survival; treatment with 50 mg of either drug per kg per day resulted only in the pr olongation of time to death. These results suggest that synercid may be use ful for treatment of toxoplasmosis in humans.