Antiparasitics: Uses, common brands, and safety info

There are three main pathogen categories of parasites that can cause infectious diseases in humans: protozoa, helminths, and ectoparasites. Altogether, they cause an enormous burden of disease in many areas of the world. While this impact is greatest in rural areas of low-income countries, parasitic infections also affect those living in developed countries, including the United States. Anyone can become infected with a parasite, but there are groups of people at a higher risk—including certain racial or ethnic minority groups, persons born outside of the United States, and people with lower socioeconomic status. In the United States, parasitic diseases of priority include Chagas disease, cyclosporiasis, cysticercosis, toxocariasis, toxoplasmosis, and trichomoniasis.

Here, we will discuss antimicrobial treatment for parasitic infections, including safety and tolerability.

Other antiparasitics:

• Artesunate

• Tinidazole

• Primaquine

• Ambisome (liposomal amphotericin B)

• Impavido (miltefosine)

• Alinia (nitazoxanide)

• Lindane

• Nix (permethrintopical)

What are antiparasitics?

Antiparasitic agents are a class of anti-infective medications used in the management and treatment of infections caused by parasites. Antiparasitic drugs include numerous subclasses of medications that cover a range of diseases caused by parasites. Parasitic infections are associated with several morbidities and can cause death. Certain parasitic infections are public health concerns, including trichomoniasis–which is estimated to be the most prevalent nonviral sexually transmitted infection (STI) worldwide.

In specific scenarios, antiparasitic agents are recommended in only certain patient populations as some parasite infections can resolve on their own without targeted treatment in otherwise healthy individuals. An example of this is toxoplasmosis. Toxoplasmosis is estimated to have caused infection in 11% of the United States population aged 6 years and older, yet very few with a well-functioning immune system develop symptoms because the infection is kept in check. However, in those with impaired immune systems, such as during pregnancy or in the HIV patient population, those infected can become very ill. Other times, treatment recommendations are dependent upon specific stages associated with infection, such as acute versus chronic Chagas Disease in adults older than 50 years of age.  

Due to the worldwide burden of parasitic infections, ongoing drug discovery for new drugs that are safe and effective is important to the well-being of all, particularly among the world’s poorest populations that are at increased risk of infection.

How do antiparasitics work?

Our understanding of exactly how many antiparasitic drugs work in getting rid of parasites remains unclear. Many antimalarial medications work in ways that result in the build-up of toxic heme which damages the parasites. Antibabesial agents target specific proteins which result in dysfunction within the parasite. Antiamebic agents work by many different mechanisms, ranging from preventing the production of certain proteins necessary for the parasite’s survival to causing reactions that accumulate toxic products within the parasite.

Anthelmintics also have multiple mechanisms of action depending upon the type of parasitic worm targeted. In general, they function by killing the worm infesting the body or by expelling them from the body.

Ectoparasiticides tend to function in ways that exert toxic effects on the nerves of the parasites, essentially paralyzing them.

What are antiparasitics used for?

Antiparasitic drugs are medications employed to manage infections caused by various protozoa, helminths, and ectoparasites. Conditions are best broken down based on the type of parasite inflicting infection.

Protozoa: single-celled organisms

• Malaria, either for treatment or as part of a prevention regimen when traveling abroad

• Babesiosis

• Toxoplasmosis

• Infections caused by amoebas, including Granulomatous Amebic Encephalitis (GAE) and Amebiasis

• Chagas disease (American Trypanosomiasis)

• Sleeping sickness (African Trypanosomiasis)

• Leishmaniasis

• Trichomoniasis

• Giardia, which can cause severe diarrhea

Helminths: parasitic worms

• Enterobiasis, also known as pinworm

• Soil-transmitted helminths (STH), which includes Ascaris, hookworm, and whipworm

• Schistosomiasis

• Echinococcosis

• Strongyloides

Ectoparasites: parasites that live externally on the skin of hosts

• Lice

• Scabies

• Fleas 

• Mites

Types of antiparasitics

Antiprotozoal Agents

Antimalarials

The drug employed to treat malaria depends on the specific species of Plasmodium causing infection, the geographic region of the infecting species, and the severity of the patient’s infection. Chloroquine and in some cases its derivatives are generally considered the drug of choice to manage uncomplicated malaria caused by all Plasmodium species except Plasmodium falciparum due to increased rates of drug resistance. In the setting of P. falciparum resistance, combinations of medications such as Malarone (atovaquone-proguanil) or Coartem (artemether and lumefantrine) should be used. In situations of severe malarial infections, intravenous medications are usually prescribed, including artesunate.

Antibabesial agents

Babesiosis management includes Mepron (atovaquone) plus Zithromax (azithromycin), which is better tolerated than the previous standard of Cleocin (clindamycin) plus Qualaquin (quinine).

Anti-toxoplasma agents

Sulfadiazine combined with Daraprim (pyrimethamine) is the first-line therapy for the management of toxoplasmosis. Bactrim (trimethoprim-sulfamethoxazole) is an alternative option with similar efficacy to the first-line regimen and is available as an intravenous formulation. Daraprim (pyrimethamine) plus Cleocin (clindamycin) is an additional option in patients with an intolerance to sulfa antibiotics.

See related: Most expensive drugs of 2019

Antiamoebic agents

Entamoeba histolytica infection is associated with both gastrointestinal and extraintestinal syndromes. The selection of medication is dependent on presentation. Antiamoebic agents which act locally on parasites confined in the intestine include Humatin (paromomycin sulfate), whereas medications used in extraintestinal presentations include Flagyl (metronidazole). Management of Acanthamoeba species, which can cause GAE, require combination therapies including Pentam (pentamidine).

Trypanocidal agents

Chagas disease, also known as American trypanosomiasis, is caused by Trypanosoma cruzi. Benzimidazole drugs, such as benznidazole, are used to manage this infection.

Antileishmanial agents

Leishmania species cause three clinical syndromes: visceral leishmaniasis (VL), cutaneous leishmaniasis (CL), and mucocutaneous leishmaniasis (ML). The drug of choice for VL in the United States is AmBisome (liposomal amphotericin B), which punches holes in the cell membranes of the parasite, resulting in its death. Impavido (miltefosine) is an oral option for VL. CL may resolve on its own without treatment, so the decision to treat is often based on a case-by-case basis considering the location of the lesions, the geographic region of acquisition of the infection (and likely infecting species) as well as patient preference. AmBisome (liposomal amphotericin B) has also been used successfully to treat CL and ML.

Anti Trichomoniasis agents

Flagyl (metronidazole) is the drug of choice for Trichomoniasis.

Antigiardial agents

Giardia is managed using Flagyl (metronidazole). Alternatives include tinidazole and Albenza (albendazole).

Anthelmintics

Anticestodal drugs

Biltricide (praziquantel) and pyrantel are broad-spectrum anthelmintics that directly kill parasitic worms like pinworm and hookworm. Alinia (nitazoxanide) is an alternative in the management of tapeworms. Albenza (albendazole) is another broad-spectrum antiparasitic drug that can be used first-line for some cestodes, including Echinococcosis.

Antitrematodal drugs

Biltricide (praziquantel) is also widely effective in managing infections caused by trematodes (flukes).

Antinematodal drugs

Albenza (albendazole) is employed to manage most infections caused by nematodes (roundworms), with Emverm (mebendazole) as an alternative. Stromectol (ivermectin) is the drug of choice for onchocerciasis – an infection caused by Onchocerca volvulus transmission by a specific species of blackflies in certain areas of Africa and South America.

Ectoparasiticides

Antiscabietic agents

Scabies is a highly contagious infectious disease, with management achieved using lindane, permethrin, or Stromectol (ivermectin). Due to drug resistance to lindane and permethrin, combinations of topical permethrin with oral ivermectin have resulted in better cure rates.

Pediculicides

Infestation with head lice is also managed with permethrin. Concerns for rising drug resistance have resulted in alternative management recommendations using Stromectol (ivermectin).

Who can take antiparasitics?

Can men and women take antiparasitics?

Antiparasitic agents are effective medications in eliminating parasitic infections. Under the guidance of a healthcare professional, they are generally considered safe with some adverse effects that can be anticipated and managed.

Primaquine is one exception in that it comes with the possibility of a more severe side effect in individuals with an inherited enzyme deficiency of glucose-6-phosphate dehydrogenase (G6PD). G6PD is an enzyme important for the survival of red blood cells, and exposure to “stressors,” including primaquine, can result in severe anemia. Primaquine should also be used wit caution in patients with a tendency to have low white blood cells, either due to other conditions or medications, because it may worsen the white blood cell count.

Can you take antiparasitics while pregnant or breastfeeding?

Some antiparasitic drugs come with clear recommendations to avoid during pregnancy due to direct links with fetal harm, including benznidazole, primaquine, and Impavido (miltefosine). Albenza (albendazole) is recommended to be avoided in the first trimester of pregnancy and can be used preferentially in the second and third trimesters if the benefit exceeds the risk.

Lindane comes with the risk of possible neurologic abnormalities in the fetus if used during pregnancy, including neural tube defects. Lindane is excreted in breast milk, and it is recommended that nursing mothers interrupt breastfeeding (or express and discard milk) for at least 24 hours following use. Also, skin-to-skin contact between the infant and the area to which lindane is applied should be avoided.

A healthcare provider is the best source of information when considering the use of antiparasitic agents while pregnant or breastfeeding. While some of the medications used carry risks to the developing fetus, untreated parasitic infections also come with severe risks.

Can children take antiparasitics?

In general, children infected with parasites benefit from treatment. Albenza (albendazole) and Emverm (mebendazole) are well tolerated among children over 12 months of age at appropriate doses, with minimal side effects reported.

Several medications should be used with caution in children for various reasons and are included on the Key Potentially Inappropriate Drugs in Pediatrics (KIDs) list. These include:

• Zithromax (azithromycin): should be avoided in neonates due to the risk of hypertrophic pyloric stenosis, a blockage of the passage out of the stomach into the small intestine.

• Bactrim (sulfamethoxazole-trimethoprim): sulfonamide medications should be avoided in neonates due to the risk of kernicterus, a type of brain damage that can result from high levels of bilirubin in a baby’s blood.

• Stromectol (ivermectin): should be avoided in infants less than 1 year of age due to the risk of encephalopathy, in which the functioning of the brain is affected.

• Ovide (malathion): should be avoided in infants less than 1 year of age due to the risk of increased absorption and possible related side effects.

The benefit of using these medications in the management of parasitic infections without effective alternatives may outweigh the risks, so decisions on treatment should always be in consultation with a healthcare professional.

Lindane is associated with neurologic toxicity and should be used in caution in children; furthermore, it should not be used in premature infants or any individual with known uncontrolled seizure disorders.

Can seniors take antiparasitics?

There are no specific reasons seniors cannot take antiparasitics, but many of the same risks in use by men, women, and children also apply. Primaquine should be avoided in those with a known G6PD deficiency or low white blood cells, and lindane should be used with extreme caution in seniors due to the risk of neurotoxicity. Lindane should be avoided entirely in anyone with an uncontrolled seizure disorder.

Seniors may also require some dose adjustments based on differences in renal function, or increased monitoring if on multiple other medications in the scenario of other conditions. For example, some antiparasitic medications can increase the QTc interval on an echocardiogram, which is associated with poor cardiac outcomes. If an individual has a prolonged QTc at baseline or is on other medications which can prolong the QTc interval, caution should be exercised when starting additional medications which can impact the QTc interval.

Are antiparasitics safe?

Certain antiparasitics do carry black box warnings. Flagyl (metronidazole) and tinidazole have been found to be carcinogenic in mice and rats, so use should be reserved for approved conditions. Cleocin (clindamycin) has been associated with severe colitis which may end fatally, and so should also be reserved for serious infections for which less toxic alternatives are inappropriate. Qualaquin (quinine) is associated with hematologic toxicity that can also result in severe renal impairment so use should be limited to approved conditions, lindane is associated with neurotoxicity which may result in seizures and death, and Impavido (miltefosine) is contraindicated for use in pregnancy due to the risk of fetal harm.

Warnings

Benznidazole carries an additional warning that it may be carcinogenic and teratogenic, so appropriate precautions for receiving, handling, administration, and disposal should be employed. The National Institute for Occupational Safety and Health (NIOSH) recommends that precautions include wearing a single pair of gloves when handling intact capsules or tablets. NIOSH recommends additional precautions if handling an oral liquid of this medication.

Recalls

• There are no current recalls as of December 2021.

Restrictions

• Qualaquin (quinine) must be dispensed with an FDA-approved medication guide.     

• Humatin (paromomycin sulfate) is only available through a specialty pharmacy.

• Any of these medications should be avoided in the setting of a known allergy to any of the active or inactive ingredients.

Are antiparasitics controlled substances?

• No, antiparasitics are not controlled substances.

Common antiparasitics side effects

Antiparasitics can cause several side effects based on the specific drug and the targeted parasitic infection treated. The following are general common side effects common to most antiparasitics:

• Abdominal pain

• Nausea

• Vomiting

• Diarrhea

• Hepatitis

• Headache

• Skin rash

• Itching

How much do antiparasitics cost?

Antiparasitics have a wide cost range depending on the specific drug, quantity, and dosage. Most medications are available in generic formulations, keeping costs low. However, some of these medications carry such niche indications their cost can be several hundreds of dollars. A SingleCare Prescription Discount Card could reduce prescription costs significantly.