Histological alterations and drug concentrations in endocysts and cyst fluid of hydatid cyst harboring in mice treated with praziquantel

Whcn mice infected with secondary Echinococcus gronul,osus were treated ig with praziquantel 400-800 mg/kg daily for 10-14 d, only a slight efficacy of the drug was observed. After ig praziquantel500 mg/(kg-d) to the infected mice for 7 d, a few cysts were damaged in local parts of germinal layer. If the cysts were kept in 20% calf serum-RPMI 1640 and exposed in vitro to praziquantel 20 and 100 ug/ml for 7 d, more cysts were damaged in local or extensive parts of the germinal layer. Praziquantel entered the endocyst and cyst fluid rapidly with the concentration of about 6 Vg/g or ml in praziquantel 20 Vg/ml group and about 30 Vg/g or ml in 100 yg/ml group. When praziquantel 400 mg/kg was given ig twice at a 4-h interval to infected mice, no accumulation of the drug in plasma or cysts was detected. After each medication. the drug peak concentrations in endocyst and cyst fluid were 2.8 yg/g and 2.1 yg/ml, respectively, namely, about 14-20% of those found in plasma. These results indicate that the cyst germinal layer is less susceptible to praziquantel and the drug concentration level is not sufficient to damage the germinal layer in cysts even when praziquantel 500 mg/kg was given to the mice.