Praziquantel, the active ingredient of Droncit Spot-on is a pyrazinoisoquinoline derivative used widely as an anthelmintic for both human and veterinary medicine. The chemical name for this substance is 2-cyclohexyl-carbonyl[1,2,3,6,7,11b] hexahydro-4H-pyrazino-[2,1-a]isoquinolin-4-one¹. ATCVet Code: QP52AA01.
Praziquantel is effective against all stages of development of intestinal tapeworms. The substance is very rapidly absorbed and distributed throughout the parasite. Both in vivo and in vitro studies have shown that praziquantel causes severe damage to the parasite integument, resulting in contraction and paralysis. There is an almost instantaneous tetanic contraction of the parasite musculature and a rapid vacuolisation of the syncytial tegument. This rapid contraction has been explained by changes in divalent cation fluxes, particularly calcium.
Praziquantel is absorbed very rapidly and almost completely in the stomach and small intestine. Studies of the behaviour following oral administration have been conducted in rats, dogs, monkeys, sheep and humans. Depending on species, maximum serum levels are reached within 0.3 to 2 hours. The chemical is evenly distributed to all organs. The elimination half-lives of 14C-praziquantel and its metabolites are between 2 and 3 hours in rats, dogs, monkeys and sheep.
Praziquantel is rapidly metabolised in the liver in both humans and animals with the 4-hydroxycyclohexyl derivative as the main metabolite. Praziquantel is completely eliminated from the body within 48 hours; irreversible binding to body constituents has not been observed. Elimination is in the form of metabolites with virtually no parent compound excreted. Between 40% and 71% of the substance is eliminated in the urine and 13%-30% in the faeces.