A light and electron microscopic study on the synergistic effect of pyrantel and the febantel metabolite febendazole on adult Toxocara canis in vitro.

In the present study, we investigated the in vitro effects on the motility and morphology of tissues and organs of Toxocara canis of the two drug components of Drontal Plus and Welpan, pyrantel and fenbendazole (the active metabolite of the prodrug febantel), both alone and in combination. Although there was no significant difference observable between the effects of the single drugs and the drug combination on worm motility, the synergistic effect of pyrantel and fenbendazole was manifested by morphological alterations seen by light and electron microscopy. Thus, an earlier onset of damage to worm tissues and organs could be observed compared to the application of the individual drugs. In addition, a higher degree of damage and an increased number of vital organs were involved. There was dramatic, significantly greater and irreversible damage to the hypodermis, longitudinal muscle, intestine, nerve cords and genital organs induced by the pyrantel/fenbendazole combination. We hypothesise that these synergistic effects will also take place when dogs are treated either with Drontal Plus or Welpan in which lower dosages will be sufficient to destroy the worms.