Q5 LONG ANSWER 10M ★ High-yield

Classify anthelmintic drugs. Describe the antiamoebic drugs and the treatment of visceral leishmaniasis.

Pharmacology · 2nd Professional — Para-Clinical

Anthelmintics — Classification and Mechanisms

Drug	Mechanism	Chief uses
Albendazole, mebendazole	Bind parasite beta-tubulin and prevent microtubule assembly, blocking glucose uptake; the worm is immobilised and dies	Ascaris, hookworm, Trichuris, Enterobius; albendazole also for neurocysticercosis and hydatid disease; broad and well tolerated
Ivermectin	Opens glutamate-gated chloride channels in invertebrate nerve and muscle, causing paralysis; these channels are absent in man, and the drug does not cross the intact blood–brain barrier	Strongyloides, onchocerciasis, filariasis, scabies, head lice
Diethylcarbamazine (DEC)	Alters microfilarial surface, promoting phagocytosis	Lymphatic filariasis — the mainstay of India’s elimination programme; causes a mazzotti-like reaction from dying microfilariae
Praziquantel	Increases membrane permeability to calcium, causing sustained contraction and tegument damage	All schistosomes, tapeworms (Taenia, Diphyllobothrium), neurocysticercosis, liver flukes
Pyrantel pamoate	Depolarising neuromuscular blocker in the worm — spastic paralysis	Ascaris, hookworm, Enterobius; must not be combined with piperazine, which acts oppositely
Niclosamide	Uncouples oxidative phosphorylation	Tapeworms; not absorbed

CLINICAL PEARL

Killing the worm can be more dangerous than the worm itself. Dying parasites release antigen, producing the mazzotti reaction in onchocerciasis, and in neurocysticercosis the inflammatory response around dying cysts causes cerebral oedema and seizures. That is why corticosteroids and anticonvulsants are given alongside albendazole in neurocysticercosis, and why treatment is avoided in ocular cysticercosis.

Mass Drug Administration and Programmes

Soil-transmitted helminths — India’s National Deworming Day gives albendazole to all children twice yearly, improving growth, haemoglobin and school attendance at negligible cost
Lymphatic filariasis — annual mass administration of DEC with albendazole, increasingly the triple regimen with ivermectin, has brought India close to elimination
Treat the whole household in enterobiasis, and repeat after 2 weeks, since reinfection is the rule
Sanitation and footwear matter more than any drug in the long term for soil-transmitted helminths

Antiamoebic and Antiprotozoal Drugs

Drug	Site of action	Notes
Metronidazole, tinidazole	Tissue amoebicide — acts on trophozoites in the gut wall, liver and other tissues	A prodrug reduced to a cytotoxic intermediate only in anaerobic organisms — the basis of selectivity. Amoebic liver abscess, invasive dysentery, giardiasis, trichomoniasis, and anaerobic bacterial infection. Metallic taste, nausea, peripheral neuropathy with prolonged use, and a disulfiram-like reaction with alcohol
Diloxanide furoate, paromomycin	Luminal amoebicide — acts on cysts in the gut lumen	Must follow metronidazole in invasive amoebiasis to clear intestinal carriage and prevent relapse; also used alone for asymptomatic cyst passers
Nitazoxanide	Broad antiprotozoal	Cryptosporidium, Giardia
Pentamidine, suramin, melarsoprol	Trypanosomiasis	—

Invasive amoebiasis always requires both — a tissue amoebicide to treat the disease and a luminal amoebicide to eradicate the source. Giving metronidazole alone leaves cysts in the gut and relapse follows

Drugs for Visceral Leishmaniasis

Kala-azar remains endemic in Bihar, Jharkhand, West Bengal and Uttar Pradesh, and India has committed to its elimination
Liposomal amphotericin B — now first-line; a single-dose regimen is effective and is the basis of the elimination programme
Miltefosine — the first effective oral agent; causes vomiting and diarrhoea, and is teratogenic with a long half-life, so contraception is required for months afterwards
Paromomycin — intramuscular, cheap; used in combination regimens
Pentavalent antimonials (sodium stibogluconate) — formerly standard, now abandoned in Bihar because of widespread resistance; cardiotoxic and pancreatotoxic
Combination and single-dose regimens reduce cost, duration, resistance and the need for hospital admission — all decisive for a programme in rural India

Common Helminth Infections and Their Treatment

Infection	Drug of choice
Ascariasis, hookworm, trichuriasis	Single-dose albendazole 400 mg
Enterobiasis (pinworm)	Albendazole or mebendazole, repeated after 2 weeks, treating the whole household
Strongyloidiasis	Ivermectin — essential before immunosuppression, since hyperinfection syndrome is often fatal
Lymphatic filariasis	DEC with albendazole, increasingly with ivermectin as triple therapy
Neurocysticercosis	Albendazole with corticosteroids and anticonvulsants; imaging first, and ocular lesions excluded
Hydatid disease	Albendazole with surgery or pair (puncture, aspiration, injection, reaspiration)
Taeniasis	Praziquantel or niclosamide
Schistosomiasis	Praziquantel
Scabies and pediculosis	Topical permethrin; oral ivermectin for crusted scabies and outbreaks

Applied Aspects

Give albendazole with a fatty meal for systemic disease such as neurocysticercosis and hydatid, since absorption is otherwise poor; for intestinal worms absorption does not matter
Add corticosteroids before albendazole in neurocysticercosis, and treat seizures; imaging must precede treatment, and ocular lesions must be excluded
Warn about alcohol with metronidazole during and for 48 hours after
Follow every course of metronidazole for amoebiasis with a luminal amoebicide
Ivermectin is contraindicated in heavy Loa loa infection because of fatal encephalopathy, and is avoided in young children and pregnancy
Deworming is cheap, safe and one of the highest-value public health measures available in India, with measurable effects on nutrition, anaemia and school performance
Screen and treat for Strongyloides before corticosteroids or other immunosuppression in anyone from an endemic area; hyperinfection syndrome carries a very high mortality
Praziquantel is given with food and causes transient abdominal pain and dizziness; it must not be used in ocular cysticercosis
Treat the household and wash bedding in enterobiasis; treating the index child alone guarantees reinfection
Sanitation, safe water and footwear prevent soil-transmitted helminth infection permanently, while deworming only clears the current burden — both are needed, and only one is a drug
Amoebic liver abscess rarely needs drainage; metronidazole alone usually suffices, and aspiration is reserved for large left-lobe or impending-rupture lesions
Distinguish amoebic from pyogenic liver abscess before treating — serology, the clinical picture and the response to metronidazole all help, and the management differs
Mass drug administration works only with high coverage, sustained over several rounds; partial coverage neither interrupts transmission nor justifies the effort
Ivermectin has a remarkable safety record and has been given to hundreds of millions in onchocerciasis programmes, which is why its role in filariasis elimination has expanded
Anthelmintics are among the safest drugs in the pharmacopoeia, which is what makes mass administration to whole populations of children defensible — the benefit is modest per child but the risk is close to zero
Albendazole is avoided in the first trimester but is given in later pregnancy in endemic areas, where hookworm anaemia does more harm than the drug

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