Compare the mechanism and tissue distribution of albendazole and mebendazole against gastrointestinal nematodes.

• A. Both inhibit microtubule polymerization by binding beta-tubulin; albendazole has higher systemic absorption and broader tissue distribution; mebendazole is more limited in systemic distribution
• B. Albendazole inhibits DNA replication; mebendazole inhibits protein synthesis
• C. Albendazole acts on eggs only; mebendazole acts on larvae only
• D. Both inhibit immune signaling

Answer: (A)

Both drugs are benzimidazoles that work by binding to parasite beta-tubulin and blocking microtubule polymerization. When microtubules can’t form properly, the parasite can’t maintain its cytoskeleton or take up glucose effectively, leading to energy depletion, immobilization, and death.

The difference lies in how much of the drug gets into the body’s tissues. Albendazole is absorbed reasonably well after oral dosing, especially with a fatty meal, and is converted to an active metabolite that distributes widely in the body. This systemic distribution lets it reach not only worms in the gut but also migrating larvae and other tissue stages, broadening its reach beyond the lumen.

Mebendazole, on the other hand, has poor systemic absorption and stays largely in the gut lumen. It achieves high local concentrations where the worms are but little drug reaches distant tissues, so its activity is mainly against luminal gastrointestinal nematodes.

So, they share the same mechanism, but albendazole’s broader tissue distribution accounts for its wider potential activity, whereas mebendazole is primarily effective where it remains concentrated—in the gut.