Albendazole and mebendazole work by which mechanism?
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Clinical Pharmacology · Antifungal and Antiparasitic Medications
Anthelmintic Medications
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Anthelmintics kill or paralyze parasitic worms; drug choice depends on the worm family: nematodes (roundworms), cestodes (tapeworms), or trematodes (flukes). Benzimidazoles disrupt worm microtubules and glucose uptake; ivermectin exploits a chloride channel unique to invertebrates; praziquantel disrupts calcium handling in tapeworms and flukes; pyrantel pamoate paralyzes worms for expulsion; diethylcarbamazine targets filarial worms. Matching drug to worm family, and managing inflammation from dying parasites, are the core concerns.
The college version
Three Worm Families
Nematodes (roundworms) include pinworm, ascaris, hookworm, whipworm, and strongyloides. Cestodes (tapeworms) are flat, segmented worms from undercooked meat or contaminated water, as in hydatid disease. Trematodes (flukes) include blood flukes causing schistosomiasis. Some drugs span multiple families; others are family-specific.
Benzimidazoles: Albendazole and Mebendazole
These bind parasite beta-tubulin, blocking microtubule assembly and glucose uptake, which starves the worm. Both cover pinworm, roundworm, hookworm, and whipworm; albendazole also treats tissue disease like neurocysticercosis and hydatid cysts. A key paradox: fatty food boosts albendazole's absorption, helpful for tissue infection, but for intestinal-only infection, poor absorption is an advantage, keeping drug concentrated in the gut. Prolonged courses need liver function and blood count monitoring for hepatotoxicity and myelosuppression.
Ivermectin
Ivermectin opens glutamate-gated chloride channels present in invertebrate nerve and muscle but absent in mammals, selectively paralyzing the parasite. It treats strongyloidiasis, onchocerciasis, and scabies. Mass death of microfilariae in onchocerciasis causes the Mazzotti reaction: itching, rash, and fever. A serious caution is Loa loa co-infection, where heavy microfilarial burden can trigger encephalopathy during rapid die-off.
Praziquantel
Praziquantel increases the parasite membrane's calcium permeability, causing sustained contraction, paralysis, and surface damage exposing the worm to immune attack. It is preferred for schistosomiasis and most tapeworms.
Pyrantel Pamoate and Diethylcarbamazine
Pyrantel pamoate is a depolarizing neuromuscular blocker causing spastic paralysis, so the worm loses its grip on the gut wall and is expelled; it's common for pinworm and roundworm. Diethylcarbamazine treats filarial worms causing lymphatic filariasis.
Shared Practical Themes
For pinworm, treating household contacts plus hygiene and laundry measures interrupts reinfection. Regimens often repeat the dose after an interval to catch newly hatched worms missed the first time. Treating tissue-dwelling parasites often pairs a corticosteroid with the anthelmintic, since killing the organism provokes dangerous inflammation. Most anthelmintics are well tolerated, with GI upset, headache, and dizziness the common effects.
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The same idea, in plain words
Explain it like I’m 10
Imagine uninvited bugs living in a house, eating food and refusing to leave. Anthelmintic medicines are tools for evicting them. Some wreck the bug's "skeleton" so it can't move or eat (benzimidazoles). Some flip a switch only bug nerves have, so the bug goes limp (ivermectin). Some make the bug's skin leaky so its own body attacks it (praziquantel). Some freeze the bug's muscles stiff so it loses grip and gets swept out (pyrantel pamoate). There are three big "bug families," so doctors pick the tool fitting that family. Everyone in the house may need treatment, and cleaning up keeps bugs from coming back.
Check yourself
2 review questions from the chapter. Try each one, then open the answer.
A patient treated for neurocysticercosis with albendazole also starts a corticosteroid. Why?
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To blunt inflammation from dying parasites
Killing the cyst-forming parasite in the brain triggers inflammation and swelling, dangerous in an enclosed space like the skull; corticosteroids reduce that response.
A patient with heavy Loa loa co-infection is considered for ivermectin for onchocerciasis. What is the safety concern?
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Risk of encephalopathy from rapid microfilarial death
A high Loa loa microfilarial load means ivermectin can kill many organisms quickly, and rapid die-off has been linked to severe neurological complications including encephalopathy, so screening and caution are needed first.
Quick check
3 questions here. Answers stay hidden until you check.
Why is a fatty meal helpful for tissue infections but not intestinal-only infections with albendazole?
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Which reaction follows ivermectin killing large numbers of microfilariae in onchocerciasis?
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