Antihelminthic drugs are medicines that rid the body of parasitic worms.
People can become infected with parasitic worms in a number of ways. The eggs of pinworms, for example, can be transferred from person to person through contaminated food, drinking glasses, clothing, or linens. Tapeworms and roundworms may enter the body when people eat undercooked meat or fish. The worms then live inside the body and may go unnoticed if they cause no troublesome symptoms. However, if they multiply rapidly or invade a vital organ, they can cause serious and sometimes life-threatening problems. The body has no natural means of getting rid of parasitic worms, but antihelminthic drugs do the job very well. Some kill the worms on contact. Others starve or paralyze the worms, which then pass out of the body in the feces.
Each type of antihelminthic drug is effective against particular kinds of worms. For example, niclosamide is effective against tapeworms, but will not work for treating pinworm or roundworm infections.
Antihelminthic drugs are available only with a physician's prescription. They are sold as liquids and tablets (regular and chewable). Some commonly used antihelminthics are mebendazole (Vermox), niclosamide (Niclocide), praziquantel (Biltricide), pyrantel (Antiminth), and thiabendazole (Mintezol).
The proper dose depends on the patient, the type of antihelminthic drug, and the condition for which it is being taken. The number of doses per day, the time between doses, and the length of treatment may also depend on these factors.
To completely rid the body of parasitic worms, take the medicine exactly as directed, for as long as directed. A second round of treatment a few weeks later may be necessary to make sure the infection is completely cleared.
Some antihelminthic medicines work best when taken with fatty foods, such as whole milk or ice cream. Others should be taken after a light meal. Be sure to follow directions about when to take the medicine and what to take with it. People who cannot follow the directions because they are on low-fat or other special diets should check with their physicians about how to take the medicine.
Some people feel drowsy, dizzy, or less alert when using certain antihelminthic drugs. Anyone who takes these drugs should not drive, use machines or do anything else that might be dangerous until they have found out how the drugs affect them.
Although some antihelminthic drugs come in chewable tablet form, praziquantel tablets should not be chewed or held in the mouth before swallowing. This particular drug has a bitter taste that may cause gagging or vomiting, so the tablets should be swallowed whole with a sip of liquid at mealtime.
Because some kinds of worms, such as pinworms, can be passed from one person to another, everyone in the household may need to take medicine when one person is infected.
While under treatment with an antihelminthic drug, see the physician as often is recommended. The physician will check to see if the infection is clearing and will make sure no unwanted side effects exist. The physician may also suggest ways to help keep the infection from coming back. Be sure to follow these suggestions. Check with the physician if symptoms do not improve or if they get worse.
Patients being treated for hookworm or whipworm infections may need to take iron supplements. Ask the physician about this.
People with certain medical conditions or who are taking certain other medicines can have problems if they take antihelminthic drugs. Before taking these drugs, be sure to let the physician know about any of these conditions:
Anyone who has had unusual reactions to antihelminthic drugs in the past should let his or her physician know before taking the drugs again. The physician should also be told about any allergies to foods, dyes, preservatives, or other substances.
In laboratory studies of animals, some antihelminthic drugs cause birth defects or miscarriage. Others do not. There have been no reports of human birth defects caused by these drugs, but because of the animal studies, some antihelminthic drugs are not recommended for use during pregnancy. Women who are pregnant or who plan to become pregnant should check with their physicians before taking antihelminthic drugs.
Some antihelminthic drugs pass into breast milk and may cause unwanted effects in nursing babies whose mothers take the medicine. It may be necessary to stop breastfeeding before beginning treatment with this medicine and not to begin breastfeeding again until some time after treatment has ended. Breastfeeding mothers who need to take antihelminthic drugs should ask their physicians whether they need to stop breastfeeding.
Other medical conditions
Before using antihelminthic drugs, people with any of these medical problems should make sure their physicians are aware of their conditions:
Use of certain medicines
- Crohn's disease
- Liver disease
- Kidney disease
- Ulcerative colitis
- Worm cysts in the eye.
Taking antihelminthic drugs with certain other drugs may affect the way the drugs work or may increase the chance of side effects.
The most common side effects of antihelminthic drugs are dizziness, drowsiness, headache, sweating, dry mouth, dry eyes, and ringing or buzzing in the ears. These problems usually go away as the body adjusts to the drug and do not require medical treatment. The antihelminthic drug thiabendazole may cause the urine to have an unusual odor. This does not need medical attention and should go away about 24 hours after the last dose. Less common side effects of antihelminthic drugs, such as loss of appetite, diarrhea, nausea, vomiting, or stomach or abdominal pain or cramps, also may occur and do not need medical attention unless they do not go away or they interfere with normal activities.
More serious side effects are not common, but may occur. Call a physician immediately if any of these side effects occur:
- Severe diarrhea
- Severe nausea and vomiting
- Numbness or tingling in the hands or feet.
In addition, check with the physician who prescribed the medicine as soon as possible if any of these side effects occur:
- Fever, with or without sore throat
- Unusual tiredness or weakness
- Skin rash, itching, peeling, blistering, or redness
- Muscle or joint aches
- Low back pain
- Dark urine
- Painful or burning urination
- Pale stools
- Blurred vision or other eye problems
- Convulsions (seizures)
- Yellow eyes and skin.
Other rare side effects may occur. Anyone who has unusual symptoms after taking antihelminthic drugs should get in touch the physician who prescribed the drug.
Antihelminthic drugs may interact with other medicines. When this happens, the effects of one or both drugs may change, or the risk of side effects may be greater. For example, using the antihelminthic drugs pyrantel and piperazine together may make pyrantel less effective. Combining the antihelminthic drug thiabendazole with the anti-wheezing drug, theophylline, increases the risk of side effects from theophylline. Anyone who takes antihelminthic drugs should tell the physician about all other medicines he or she is taking.
- Inflammation of the colon (large bowel).
- (Also called stool.) The solid waste that is left after food is digested. Feces form in the intestines and pass out of the body through the anus.
- A false or distorted perception of objects, sounds, or events that seems real. Hallucinations usually result from drugs or mental disorders.
- A single, independent life form, such as a bacterium, a plant or an animal.
- An organism that lives and feeds in or on another organism (the host) and does nothing to benefit the host.
- Of, or relating to a parasite.
Gale Encyclopedia of Medicine. Gale Research, 1999.