Anthelmintics: Uses, common brands, and safety info

Anthelmintic is the term used to describe any drug used to treat parasitic worm (helminths) infections in humans and animals. Helminth infections are some of the most common infections in the world in animals (both companion animals such as dogs and cats and production animals such as cattle), as well as in humans in countries primarily in tropical regions. In many of these countries helminth infections pose a large threat to public health and, although rarely fatal, lead to serious conditions such as anemia, malnutrition, and reduced immunity status. Parasitic worms that cause infection in humans mainly include roundworms, tapeworms, and flukes.

The following table lists the anthelmintic medications approved for human use by the U.S. Food and Drug Administration (FDA), followed by information on how antiparasitic drugs work, what conditions they treat, safety, and cost.

Other anthelmintics

• Hetrazan (diethylcarbamazine)

• Moxidectin

• Piperazine

• Egaten (triclabendazole)

What are anthelmintics?

Over the past 50 years, safe and effective anthelmintic drugs have been developed for parasitic worm infections in humans and for animal health. The early anthelmintic drugs had more serious side effects, such as liver toxicity. Levamisole, for example, was an anthelmintic drug that was commonly used for the treatment of parasitic infections when introduced in 1969 but then withdrawn from the US market in 2000 because of adverse effects. Other older agents required stringent requirements such as 12-hour fasting for the patient prior to treatment. New anthelmintic therapies include broad-spectrum anthelmintics and those with anthelmintic activity more targeted to the specific infecting parasite. The newer drugs are effective and much better tolerated by patients.

How do anthelmintics work?

Anthelmintics have different types of pharmacological activity against different types of parasitic worms. Antiparasitic drugs work by either killing the worms that infest the body or by expelling them from the body. Although the exact mode of action may be unknown, the theories for each specific drug class are as follows:

• The benzimidazoles—Albenza (albendazole), Mintezol (thiabendazole), and Vermox (mebendazole)—interrupt parasite food intake by binding to tubulin, a protein necessary for cells to function, which prevents the worms from absorbing the sugars they need and results in the death of the parasite.

• Pyrantel pamoate activates nicotinic cholinergic receptors in the parasite’s muscle cells, paralyzing the worm so that the body can remove them naturally in the stool.

• Stromectol (ivermectin) causes paralysis and death of the parasite by stimulating excessive release of neurotransmitters in the worm’s nervous system.

• Biltricide (praziquantel) works by causing severe spasms and paralysis of the worm’s muscles, thought to be caused by a rapid calcium ion influx inside the parasite; the worms are then either completely destroyed in the intestine or passed in the stool.

• Impavido (miltefosine) stops the growth of certain parasites likely by interfering with membrane lipids and mitochondrial function causing cell death.

What are anthelmintics used for?

Anthelmintics are used to treat people who are infected by helminths, or parasitic worms. These drugs are also commonly used to treat infected animals. In humans, the classes of parasitic worms include:

• Cestodes: flatworms and tapeworms 

• Trematodes: flukes

• Nematodes: roundworms, also called whipworms, pinworms, hookworms, and threadworms

Common names for helminth infections include:

• Enterobiasis: caused by Enterobius vermicularis, a pinworm

• Acariasis: caused by ascaris worms, a type of roundworm

• Beef tapeworm: caused by Taenia saginata

• Pork tapeworm: caused by Taenia solium

• Schistosomiasis (also called bilharziasis): caused by Schistosoma, a type of fluke

• Filariasis: (also called elephantiasis) caused by filarial roundworms

• Trichuriasis: caused by Trichuris trichiura, a whipworm

Ivermectin and COVID-19

There is growing interest in the use of the anthelmintic ivermectin for the treatment or prevention of COVID-19. Ivermectin is an oral drug approved by the FDA to treat conditions caused by parasitic worms in humans. There are also topical forms of ivermectin approved to treat head lice and for certain skin conditions such as rosacea. The FDA has not authorized or approved ivermectin for use in preventing or treating COVID-19 in humans. 

There have been reports of patients who have tried to self-medicate using ivermectin intended for livestock. Veterinary formulations of ivermectin, which are approved to treat or prevent parasite infections in animals, are different from those approved for humans. The veterinary preparations are often highly concentrated because they are used for large animals like horses and cows. The use of animal ivermectin in humans is dangerous because high doses can be toxic in humans resulting in nausea, vomiting, diarrhea, hypotension (low blood pressure), allergic reactions (itching and hives), dizziness, ataxia (problems with balance), seizures, coma, and even death. 

Types of anthelmintics

Anthelmintics are separated into either chemical classes or as individual drugs based on their activity against parasitic worms. There are many anthelmintics dedicated to veterinary medicine, however, the following are the classes or individual anthelmintics by activity specifically for human use: 

• Piperazine: first used as an anthelmintic in the 1950s and used to treat common roundworms and pinworms.

• Benzimidazoles: a class of anthelmintics first discovered in 1961 that includes thiabendazole, mebendazole, and albendazole used to treat roundworms.

• Pyrantel: a treatment for several types of intestinal worms, including pinworms, used since the mid-1970s.

• Ivermectin: introduced as an anthelmintic in the 1980s used to treat roundworms.

• Miltefosine: approved for use in 2006 to treat a parasitic infection called leishmaniasis. 

Who can take anthelmintics?

Adults

In general, the safety and effectiveness of anthelmintics have been established in adults and the drugs are well tolerated and very rarely cause serious side effects. 

Children and adolescents

Children infected with parasitic worms benefit significantly from anthelmintic treatment. 

In particular, the benzimidazoles, Albenza (albendazole), Mintezol (thiabendazole), and Vermox (mebendazole), are well tolerated among children over 12 months of age at appropriate doses, with only minor side effects reported. 

Seniors

In general, clinical studies of anthelmintics did not include sufficient numbers of patients 65 and older to determine if they responded differently from younger patients. Anthelmintic treatment should be closely monitored in the elderly due to a greater likelihood of decreased liver or kidney function, and because other disease states or drug therapies might increase the risk of adverse events. 

Women who are pregnant or breastfeeding 

Treatment with anthelmintics should be avoided in pregnant women. Impavido (miltefosine) has an FDA-mandated boxed warning, also known as a “black box warning,” cautioning against its use in pregnant women. There are, however, risks to the mother and fetus associated with certain untreated helminthic infections and If treatment in pregnancy is considered to be absolutely necessary it is safest to give it in the second or third trimester.

For most anthelmintics, there is limited data regarding their presence in human milk. Treatment of mothers who intend to breastfeed should only be undertaken when the risk of delayed treatment to the mother outweighs the possible risk to the newborn. 

A woman’s healthcare provider is the best source of information when considering the use of anthelmintics while pregnant or breastfeeding.

Are anthelmintics safe?

Anthelmintics are considered safe and generally well tolerated. As stated previously, Impavido (miltefosine) carries a boxed warning regarding fetal harm and should not be taken by pregnant women.

Recalls

There are no current recalls as of September 2021.

Restrictions

You should not take any anthelmintic medicine if you are allergic to any of the active or inactive ingredients. Use caution when considering specific anthelmintic therapy if you have any of the following conditions:

• A history of prolongation of the QTc interval (a condition that can cause fast, chaotic heartbeats)

• A dose adjustment may be necessary if you have impaired kidney function

Are anthelmintics controlled substances?

No, anthelmintics are not controlled substances.

Anthelmintic resistance

The frequent use of anthelmintics has led to concerns about the development of drug resistance in parasitic worms that infect animals as well as humans, with reports of resistance to multiple classes of anthelmintics. The evidence from veterinary medicine and reports of reduced susceptibility in human helminths are of concern because there have been no new chemical classes introduced since 2000. It is thought that parasitology research for new drugs and new drug classes has slowed due to the increased costs of product development and the poor likelihood of financial return to the drug manufacturers.

Common anthelmintics side effects

Anthelmintics can cause a variety of side effects based on the specific drug and the targeted parasitic infection treated. Following are general common side effects common to anthelmintics:

• Decreased appetite

• Abdominal pain

• Diarrhea

• Flatulence

• Nausea

• Vomiting

• Dizziness

• Rash

• Itching

How much do anthelmintics cost?

Anthelmintics have a wide price range depending on the specific drug, quantity, and dosage. Almost all Medicare and insurance plans will cover anthelmintics. Since most are available in generic formulations, they are much less expensive than their brand-name counterparts. A SingleCare discount card could reduce prescription costs up to 80% at participating pharmacies.