Medication Summary
Several drugs are efficacious for the treatment of ascariasis, including the asymptomatic intestinal phase; this involves the periodic deworming of children (symptomatic and asymptomatic), a reduction of the public health burden in selected communities, treatment during the pulmonary phase (rarely), and treatment of complications of the infection (some but not all).
The drugs of choice in the United States include pyrantel pamoate and the benzimidazoles, albendazole and mebendazole. The efficacy for albendazole, mebendazole, and pyrantel is 88%, 95%, and 88%, respectively. For hookworm, a common infecting STH, the efficacies for the same medications are 72%, 15%, and 31%, respectively; therefore, using albendazole is more efficacious, when a coinfection of ascaris and hookworm is suspected.
In general, antihelminthic drugs are not recommended in patients from endemic areas (areas with large worm burdens) who have acute abdominal pain, with or without partial bowel obstruction, because of the risk of precipitating complete obstruction. This complication has particularly been associated with pyrantel pamoate, which causes a spastic (depolarizing) paralysis of the worms, increasing the potential for worm bolus formation; however, this complication has also been reported in association with piperazine, mebendazole, and albendazole. In cases with acute abdominal symptoms, conservative treatment is best and the antihelminthic should be administered after symptoms subside (see Medical Care).
In pregnancy, the drug of choice is pyrantel pamoate. It is recommended in symptomatic cases only and should be administered after the symptoms subside in response to conservative therapy (see Medical Care).
Two other alternative medications with demonstrated efficacy in the treatment of ascariasis include nitazoxanide, which was approved by the US Food and Drug Administration (FDA) in December 2002 for treatment of Giardia lamblia and Cryptosporidium parvum in patients aged 1-11 years, and levamisole, which was FDA approved in June 1990 for use in treatment of colon cancer and although has demonstrated efficacy in the treatment of ascariasis since at least the early 1980s.
Albendazole has the advantages of pediatric dosing for individuals younger than 2 years, good tolerability, and efficacy in the treatment of ascariasis, hookworm infection, pinworm infection, strongyloidiasis, and trichuriasis. Nitazoxanide has similar efficacy, but dosing has not been established in patients younger than 1 year.
The World Health Organization (WHO) recommends 4 drugs in STH control programs (ie, ascariasis, hookworm infection, pinworm infection, strongyloidiasis, and trichuriasis): albendazole, levamisole, mebendazole, and pyrantel embonate. [22, 23] All four have a cure rate of more than 90% in patients with ascariasis. Albendazole has a 60-90% cure rate for hookworm infection, 20-90% for strongyloidiasis and trichuriasis, and more than 90% for pinworm infection. Mebendazole is somewhat less efficacious. Levamisole is somewhat less efficacious for hookworm infection (20-90% cure rate) but significantly less so (20-60% cure rate) for pinworm infection, strongyloidiasis, and trichuriasis. Pyrantel embonate has poor efficacy (0-20% cure rate) for strongyloidiasis and trichuriasis.
In developing countries, many patients (50-92%) with acute abdominal symptoms compatible with partial and/or subacute bowel obstruction and a high degree of suspicion for ascariasis as the etiology (5-35% of all obstructions) respond to conservative measures without requiring surgery or progressing to sepsis (see Medical Care).
Anthelmintic agents
Class Summary
Parasite biochemical pathways are different from the human host; thus, toxicity is directed to the parasite, egg, or larvae. Mechanism of action varies within the drug class.
Mebendazole (Emverm)
Causes worm death by selectively and irreversibly blocking uptake of glucose and other nutrients in susceptible adult intestine where helminths dwell. Causes slow immobilization and death of organisms. Administration over 3 d reduces risk of worm bolus formation. Available as a 100-mg chewable tablet that can be swallowed whole, chewed, or crushed and mixed with food.
Albendazole (Albenza)
Broad-spectrum anthelmintic agent effective against Ascaris species, hookworm, tapeworm, liver fluke, and pinworms. Decreases ATP production in worm, causing energy depletion, immobilization, and finally death.
Pyrantel pamoate (Antiminth, Pin-Rid, Pin-X)
Depolarizing neuromuscular blocking agent. Inhibits cholinesterases, resulting in spastic paralysis of worm. Poorly absorbed from GI tract and partially metabolized in liver.
Piperazine citrate (Vermizine)
No longer available in the United States. Causes flaccid paralysis of the helminth by blocking response of Ascaris species worm to acetylcholine; thus, expels the worm by normal intestinal peristalsis. Readily absorbed from GI tract, partially degraded in vivo, and excreted in urine. Exhibits wide therapeutic index.
The dose of piperazine citrate is expressed in terms of piperazine hexahydrate. For example, piperazine hexahydrate 250 mg = the anhydrous form of piperazine citrate 275.75 mg. The PO solution is equivalent to 500 mg/5 mL of piperazine hexahydrate. The dosage for piperazine (granules) solution, susp, and tabs are not interchangeable.
Ivermectin (Stromectol)
Binds selectively with glutamate-gated chloride ion channels in invertebrate nerve and muscle cells, causing cell death. Half-life is 16 h; metabolized in liver.
Levamisole (Ergamisol)
Not available in the United States. L-isomer of tetramisole, a potent anthelmintic. Has demonstrated a broad range of pharmacologic activities, some of which include the modulation of the immune system. Restores immune function and stimulates T-cell activation and proliferation, monocyte function and neutrophil chemotaxis, adhesion, and mobility.
Nitazoxanide (Alinia)
Elicits antiprotozoal activity by interference with pyruvate:ferredoxin oxidoreductase (PFOR) enzyme–dependent electron transfer reaction, which is essential to anaerobic energy metabolism. Available as a PO suspension (20 mg/mL).
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The roundworm Ascaris lumbricoides causes ascariasis. Worms can reach 10-30 cm in length. Clinical disease results from effects of pulmonary larval migration, intestinal obstruction, or migration through the biliary tree.
Tables
Parasite* |
Disease |
Prevalence |
A lumbricoides |
Common roundworm infection, ascariasis |
800 million to 1.4 billion |
T trichiura |
Whipworm infection, trichuriasis |
600 million to 1 billion |
Necator americanus and Ancylostoma duodenale |
580 million to 1.2 billion |
|
Strongyloides stercoralis |
Threadworm infection, strongyloidiasis |
30-300 million |
Enterobius vermicularis |
Pinworm infection |
4-28% of children |
Toxocara canis and Toxocara cati |
Visceral larva migrans and ocular larva migrans |
2-80% of children |
*All major parasites are found in tropical, subtropical, and temperate climates. |
||
Minor Parasite |
Disease |
Distribution |
Ancylostoma braziliense |
Costal regions worldwide |
|
Uncinaria stenocephala |
Cutaneous larva migrans |
Costal regions worldwide |
Ancyclostoma canium |
Eosinophilic enteritis |
Australia |
Ancylostoma ceylanicum |
Hookworm infection |
Asia |
Oesophagostomum bifurcum |
Nodular worm infection |
North America |
Strongyloides fuelleborni |
Swollen belly syndrome |
West Africa |
Ternidens diminutus |
False hookworm infection |
Southern Africa |
