Mechanism of action of praziquantel on the eggs of Schistosoma japonicum.

The mode of action of praziquantel on Schistosoma japonicum eggs was examined in mice and in vitro. In a long term oogram observation of mouse intestine, lasting from 1 to 56 days after oral administration of 100 mg/kg 4 times in one day, many empty egg shells were observed from the next day. Immature eggs, however, were not killed, but developed into miracidia that later degenerated into granulated and calcified eggs. In the oograms of mouse, from 5 to 240 minutes after a single oral dose of 100 mg/kg of praziquantel, miracidium hatching occurred 5 minutes in the tissues after treatment. In the in vitro experiment, miracidia in eggs from cut pieces of intestine began to hatch starting 5 minutes after exposure to praziquantel at least at a concentration of 1 ng/ml and reached maximum hatching at 30 minutes and died in several minutes after hatching.