Anthelmintics - Medicines for Worms
Worms are parasites that enter the body and are able to live and feed off the person they have entered. The most common worm infection in the UK is threadworms. Medicines to treat worms are sometimes called anthelmintics. Mebendazole (trade name Vermox®) is the most commonly prescribed medicine for worms in the UK.
What are worms?
Worms (sometimes called helminths) are parasites that enter the body and are able to live and feed off the person they have entered. There are many types of worms and they are usually divided into three groups:
- Roundworms - the most common roundworm infections are thought to be caused by threadworms, ascaris, hookworms and trichuris. Roundworm eggs usually enter the body by the person eating food or drinking water that contains eggs. The eggs live and hatch in the gut (intestine).
- Tapeworms - these worms live in the gut. People usually become infected by eating raw or uncooked meat.
- Flukeworms - these worms can live in the blood vessels, gut, lungs or liver. You usually become infected with fluke worms by swimming or washing in fresh water that contains flukeworms. An infection with flukeworms causes a tropical disease called schistosomiasis.
Most worm infections occur in warm tropical countries or developing countries where food and water may not be clean. It is thought that millions of people around the world are infected with worms at any one time. In the UK the most common worm infection is threadworms - this is a type of roundworm and is sometimes referred to as a pinworm. Threadworms are spread by being in contact with someone who is already infected with threadworms. Other types of worm infections can occur if you live in the UK; however, they do not occur very often. People who get these infections have usually been travelling in countries where these types of worm infections are common.
Note: ringworm in not an infection caused by worms. It is a name given to a type of fungal skin infection.
Which medicines are usually prescribed for worms?
There are several medicines that may be used to treat worm infections - they are sometimes called anthelmintics. Mebendazole is the most commonly prescribed medicine for worms in the UK. This is because it is used to treat threadworms which are the most common worm infections in the UK. Mebendazole is also used to treat roundworm, whipworm and hookworm infections.
Other medicines that may be prescribed for the various types of worm infections include:
These medicines are not licensed for use in the UK and are specially imported to treat more unusual worm infections. They are usually prescribed by doctors who specialise in treating worm infections.
How do medicines for worms work?
Most medicines used to treat worm infections kill worms by either starving them or paralysing them; for example:
- Mebendazole, albendazole and tiabendazole work by preventing the worms from absorbing the sugars they need for survival. They kill the worms but not the eggs.
- Praziquantel, and ivermectin work by paralysing the worms in the gut (intestine). This allows them to be easily dislodged and removed from the gut in the stools (faeces).
What is the length of treatment?
In general, the length of treatment is usually quite short (at most a few days). This will depend on what type of worm you have and which medicine has been prescribed. For example, for threadworms, mebendazole is usually given as a single one-off dose. This dose may be repeated two weeks later. For whipworm or common roundworm infections, mebendazole is given twice a day for three days.
For threadworms, it is usually advised that everybody in the household be treated if possible.
What about side-effects?
It is not possible to list all the side-effects of these medicines in this leaflet. If you want more information specific to your medicine, see the information leaflet that came with your medicine.
In general, medicines for worms are well tolerated and very rarely cause serious side-effects. The side-effects most commonly reported are tummy upsets such as cramps, wind, diarrhoea and feeling sick (nausea).
Who cannot take medicines for worms?
There are very few people who cannot take a medicine for worms. If for some reason one medicine has caused a side-effect or there is a reason you cannot take one, your doctor will discuss other ways to treat you.
Mebendazole is licensed for adults and children over the age of 2. However it is used to treat children from the age of 6 months if necessary. Mebendazole is usually avoided if you are pregnant or breast-feeding.
Can I buy medicines to treat worms?
For adults and children aged over 2 years, you can buy mebendazole to treat threadworms from your local pharmacy. If you need to treat threadworms in a child younger than 2 years old, discuss this with your doctor. If you have been abroad and think you have another type of worm infection, see your doctor.
How to use the Yellow Card Scheme
If you think you have had a side-effect to one of your medicines, you can report this on the Yellow Card Scheme. You can do this online at the following web address: www.mhra.gov.uk/yellowcard.
The Yellow Card Scheme is used to make pharmacists, doctors and nurses aware of any new side-effects that your medicines or any other healthcare products may have caused. If you wish to report a side-effect, you will need to provide basic information about:
- The side-effect.
- The name of the medicine which you think caused it.
- The person who had the side-effect.
- Your contact details as the reporter of the side-effect.
It is helpful if you have your medication and/or the leaflet that came with it with you while you fill out the report.
Further reading & references
- Roundworm; NICE CKS, December 2011 (UK access only)
- Threadworm; NICE CKS, December 2011 (UK access only)
- Parasites and Health; Centers for Disease Control and Prevention
- British National Formulary; NICE Evidence Services (UK access only)
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but makes no warranty as to its accuracy. Consult a doctor or other healthcare professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Mary Harding
Prof Cathy Jackson