In this essay we will discuss about the drugs that are used for the treatment of worm infestations.
1. Drugs Used to Treat Threadworm/(Pinworm, Enterobius Vermicularis) Infestations:
These worms live in the caecal region and the females migrate to anus, where they lay eggs and cause intense itching. The scratching of the area leads to infection of the hand with eggs, which may be transferred to food and thus further infestation occurs.
i. Mebendazole:
Mebendazole is a broad spectrum anthelmintic effective against threadworm, roundworm, whipworm and hookworm infections. Absorption is minimal and 90% of the dose is passed in the feces. Mebendazole is the drug of choice for threadworm for patients of all ages over 2 years in a single dose of 100 mg. It is also the drug of choice for whipworm (Trichuris trichuira) in doses of 100 mg twice daily for 3 days.
In roundworm and hookworm infections, it is also used in doses of 100 mg twice for 3 days. Mebendazole, rarely, causes nausea and diarrhea. Hypersensitivity reaction has been reported. It is contraindicated in children under 2 years and pregnancy.
ii. Albendazole:
Albendazole is a congener of mebendazole. It has also broad- spectrum anthelmintic activity against threadworm, roundworm, hookworm, strongyloides stercoralis, whipworm, tapeworm (worms that live in the GIT) and hydatid cyst that lives in the tissues. It is used in single or mixed intestinal worm infections. Roundworm and hookworm infections respond to a single dose treatment as effectively as 3 day treatment with mebendazole.
In hydatid cyst caused by Echinococcus granulosus, albendazole is used in conjunction with surgery to reduce the risk of recurrence or as primary treatment in inoperable cases. 400 mg twice daily is given for 28 days and the treatment is repeated after a gap of 14 days. The side effects are not of great significance, when used for intestinal worms, but prolonged treatment may cause liver damage, blood disorders, convulsions and meningism in cerebral disease.
iii. Piperazine:
Piperazine is highly effective against threadworm and roundworm infections, but is not the drug of choice. It blocks the response of roundworm cell to acetylcholine and the flaccid worm is then expelled by peristalsis. Piperazine may cause GIT disturbances and allergic reactions. Rarely, it may cause Stevens-Johnson syndrome, drowsiness and clonic contractions. It is contraindicated in severe renal impairment, neurological disorders, epilepsy, pregnancy and peptic ulcer.
2. Drugs Used to Treat Roundworm (Ascaris Lumbricoides) Infestations:
Roundworms live in the small intestines. Reinfection occurs due to passage of larval forms from intestines into the lungs via blood stream from where they migrate to pharynx via trachea and are swallowed.
Levamisole:
Levamisole is the drug of choice for roundworm infection. It has nicotine like action, stimulating and subsequently blocking the neuromuscular junctions. The paralyzed worms are then passed into feces. Ova are not killed. The drug is given orally as a single dose of 120-150 mg in adults. It is rapidly absorbed and is widely distributed including the CSF. It is metabolized in the liver and excreted by the kidney. When single dose therapy is used, mild nausea or vomiting has been reported in about 1% of patients. Mebendazole and piperazine are the other drugs active against roundworms.
3. Drugs Used to Treat Hookworm/(Ancylostoma Duodenale) Infestations:
Hookworm lives in small intestine and sucks blood from the point of their attachment. Severe infection causes iron deficiency anemia. Reinfection occurs due to penetration of larvae into the skin, which passes to the intestine via the lungs. Mebendazole is the drug of choice. Pyrantel and Bephenium are anthelmintic effective in hookworm infection, but provide lower cure rates and seldom used.
4. Drugs Used to Treat Strongyloides Stercoralis Infestations:
This worm lives in the gut and produces larvae, which penetrate the gut wall and invade the tissues, setting up a cycle of autoinfection. They usually cause mild intestinal symptoms but if the patient is immunosuppressed, i.e. given large doses of steroids or has AIDS, widespread penetration of the gut occurs which may be fatal.
Thiabendazole:
Thiabendazole is the drug of choice for strongyloidiasis in adults. It is also effective against other helminths, which infest the gut namely roundworm, hookworm, threadworm and whipworm. Symptomatic relief occurs in guineaworm infection.
Thiabendazole is rapidly absorbed, metabolized by liver and excreted in urine. It is mainly used in strongyloidiasis, cutaneous and visceral larva migrants and for symptomatic relief of trichinosis. It can be used as an adjunct in hookworm, whipworm or roundworm infections. It is not suitable for mixed infection involving roundworm, because of risk of migration.
Apart from GIT disorders, thiabendazole can cause severe hypersensitivity reactions. Rarely tinnitus, collapse, severe liver damage and visual disorders are observed. It should be used with caution in hepatic or renal impairment and elderly patients. The drug should be discontinued, if hypersensitivity reactions occur. It is contraindicated in pregnancy and breast-feeding.
5. Drugs Used to Treat Tapeworm/(Taenia Saginata, Taenia Solium and Hymenolepis Nana) Infestations:
Niclosamide:
Niclosamide is the most widely used drug for the tapeworm infections. It kills the worms, which are then expelled through saline purgation. It is given in the morning on empty stomach in a dose of 1 g, which is repeated after 1 hour. This is followed 3 hours later by a saline purgative. Side effects are minimal and include nausea, retching, abdominal pain and pruritus.
6. Drugs Used to Treat Schistosomiasis Infestations:
Praziquantel:
Praziquantel the drug of choice in all forms of schistosomiasis and is free from serious side effects of drugs used earlier. It is highly effective with a cure rate of about 80%.
7. Drugs Used to Treat Filariasis/(Loa Loa, WuchereriaBancrofti and Brugia Malayi):
Diethylcarbamazine (hetrazan):
Hetrazan is effective against microfilariae and adult worms. It is orally absorbed, distributed all over the body, metabolized in liver and excreted in urine. Filariasis is treated with a dose of 1 mg/kg of hetrazan on first day to minimize reactions and increased gradually to 6 mg/kg daily for 21 days to achieve a radical cure. Hetrazan is also used for tropical eosinophilia (4 mg/kg for 4 days). Side effects include GIT disorders, arthralgia, headache and malaise. Allergic side effects due to mass destructions of microfilariae may require antihistamines and/or corticosteroids.