Anthelmintic-induced destrobilation and its influence on calculated drug efficacy in Hymenolepis diminuta infections in rats.

Anthelmintic efficacy studies typically involve direct counts of worms remaining in the host shortly after drug treatment. Few such studies, however, have considered the phenomenon of tapeworm destrobilation when determining effective dosages. The present study reports on the frequency of drug-induced destrobilation and the subsequent regeneration of Hymenolepis diminuta in rats following treatment with niclosamide or praziquantel and its implications with respect to the apparent efficacy of these anthelmintics. Drug efficacies very similar to those reported in the literature were determined upon examination of infected animals 24 hr posttreatment. Small regenerating worms were, however, observed in the small intestine of rats 8 days after treatment, indicating that destrobilated worms were present, but overlooked, during the initial examination. Within several days posttreatment, destrobilated worms can regenerate to a size that is readily apparent in the gut contents, allowing the effective dosage to be determined with much greater confidence. Due to the demonstrated ability of these destrobilated worms to regenerate to the gravid state, it is imperative that a fully effective anthelmintic dosage be determined and administered.