Which antiparasitic agent is most effective against immature stages of Fasciola hepatica?

The most effective antiparasitic agent against the immature stages of Fasciola hepatica is clorsulon. This compound specifically targets the immature flukes, which are the larval forms of the liver fluke, leading to their effective eradication. Clorsulon inhibits key metabolic pathways in these parasites, particularly affecting their ability to generate energy, which is crucial for their development and survival.

Praziquantel is primarily effective against adult trematodes and is not specifically indicated for immature stages of Fasciola hepatica. Fenbendazole, while a broad-spectrum anthelmintic, is more effective against nematodes and may have limited efficacy against flukes. Ivermectin targets a different spectrum of parasites, mainly arthropods and nematodes, and is not effective against Fasciola hepatica at any stage of its life cycle. Thus, clorsulon stands out as the appropriate choice for targeting immature forms of this particular parasite.