Antiparasitic Drugs
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Antiparasitic drugs can be used for prophylaxis and for treatment.
It is helpful to understand the parasite life cycle when determining treatment regimens.
Prophylaxis is most commonly used for malaria (Plasmodium). However, the fact that drugs are used at lower doses for prophylaxis has led to emergence of resistance.
Treatment of parasites must often be done at a population level, where infections are frequently asymptomatic and where humans act as a principal reservoir.
Parasites unfortunately represent the majority of neglected diseases in the world, and research and development into new, more effective and less toxic treatments is slow. However, progress is being made, through efforts of thr WHO and MSF.
Antiparasitic drugs include:
- pyrantel pamoate
- mebendazole
Pyrantel pamoate is a broad-spectrum antihelmintic agent.
- enterobius vermicularis
- ascaris lumbercoides
- trichostrongylus orientalis
- hookworm
Mechanism
- depolarizing neuromuscular blocking agent, causing release of acetylcholine and inhibition of cholinesterase
- results in stimulation of ganglionic receptors and worm paralysis, followed by expulsion
Dose and Half Life
- standard dose is 11 mg/kg, with a max of 1 g
- for pinworm, a single dose is repeated at 2 and four weeks, with cure rates higher than 95%
- for ascaris, pyrantel is given as a single dose, with cure rates from 85-100%
Adverse Drug Reactions
Adverse effects occur in 4-20% of patients and are usually mild and transient. They can include:
- nausea, vomiting, diarrhea, abdominal cramps
- dizziness, drowsiness, headache, insomnia
- rash, fever, weakness
There are no contraindications, but it should be used with caution in patients with liver dysfunction.
Mebendazole
- Ascaris lumbercoides
- Enterobius vermicularis
- other nematodes
Mechanism
- Inhibits microtubule synthesis
Single-dose regimens of oral albendazole (Albenza), mebendazole (Vermox), and pyrantel pamoate are effective against Ascaris lumbricoides. Only albendazole is effective against hookworm. No single-dose regimen appears effective against Trichuris trichiura.
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