Helminths have complex life-cycles, special knowl edge of which is required by those who treat infections. Table 14.5 will suffice here. Drug resistance has not so far proved to be a clinical problem, though it has occurred in animals on continuous chemoprophylaxis.
Drugs for helminthic infections
Albendazole is similar to mebendazole (below).
Diethylcarbamazine kills both microfilariae and adult worms. Fever, headache, anorexia, malaise, urticaria, vomiting and asthmatic attacks following the first dose are due to products of destruction of the parasite, and reactions are minimised by slow increase in dosage over the first 3 days.
Ivermectin may cause immediate reactions due to the death of the microfilaria (see diethylcarbamazine). It can be effective in a single dose, but is best repeated at 6-12-month intervals.
Levamisole paralyses the musculature of sensitive nematodes which, unable to maintain their anchorage, are expelled by normal peristalsis. It is well tolerated, but may cause abdominal pain, nausea, vomiting, headache and dizziness.
Mebendazole blocks glucose uptake by nematodes. Mild gastrointestinal discomfort may be caused, and it should not be used in pregnancy or in children under the age of 2.
Metriphonate is an organophosphorus anticholinesterase compound that was originally used as an insecticide. Adverse effects include abdominal pain, nausea, vomiting, diarrhoea, headache and vertigo.
Niclosamide blocks glucose uptake by intestinal tapeworms. It may cause some mild gastrointestinal symptoms.
Piperazine may cause hypersensitivity reactions, neurological symptoms (including 'worm wobble') and may precipitate epilepsy.
Praziquantel paralyses both adult worms and larvae. It is extensively metabolised. Praziquantel may cause nausea, headache, dizziness and drowsiness; it cures with a single dose (or divided doses in one day).
Pyrantel depolarises neuromuscular junctions of susceptible nematodes which are expelled in the faeces. It cures with a single dose. It may induce gastrointestinal disturbance, headache, dizziness, drowsiness and insomnia.
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