Antiprotozoals are medications that are given to treat infections of the parasite protozoa. These include malaria, trichomoniasis and giardiasis.

  1. Treat parasitic infections.
  2. Available in two forms: antimalarials and miscellaneous.
  3. Malarial infections are common to Africa and South-East Asia. 

If you have any concerns relating to infections from parasites or would like to consult a registered clinician about antiprotozoals, our online video consultation service is available from 9.30am-4.30pm, five days a week. 

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Product information

What are antiprotozoals?

Antiprotozoals are drugs that are prescribed to treat parasite infections called protozoa. The most common of these is malaria, but it may also be used to treat trichomoniasis and giardiasis. The medication comes in two forms, antimalarials and miscellaneous, which essentially means non-malarial, protozoa infections. 

In some circumstances, the antiprotozoals metronidazole and doxycycline can be prescribed to treat bacterial infections. It is not fully understood how antiprotozoals work, but it is thought that they interfere with the infection’s DNA, and therefore prevent it from spreading further.

What is malaria?

If you feel unwell after visiting an area where malaria is found, you should seek immediate medical attention. 

Malaria is a serious condition that is spread by certain types of mosquito. Just one bite can be enough to infect someone, and if it isn’t diagnosed and treated quickly it can be fatal. Symptoms of malaria can present within seven days of the original infection, although in some cases it can take up to a year, depending on the specific parasite. In 

most cases, however, people become symptomatic within one and three weeks of being infected. 

What symptoms does malaria cause?

Symptoms include a fever, shivers, diarrhoea, vomiting, headaches, muscle pain and feeling generally unwell. In many cases, these symptoms are quite mild and can go undiagnosed. The most serious type of malarial infection is caused by the plasmodium falciparum parasite, which, if not treated quickly, can lead to respiratory or organ failure. 

What types of malaria are there?

The plasmodium parasite comes in many forms, but only five of these affect humans. These are the previously mentioned plasmodium falciparum (which is found in Africa and is responsible for most malaria related deaths worldwide), plasmodium vivax (found in Asia and South America, which produces milder symptoms that occur in relapses for up to three years), plasmodium ovale (most common in West Africa, it can remain in the system for up to ten years without presenting symptoms), plasmodium malariae (a rare form that is found in Africa) and plasmodium knowlesi (the rarest of all malarial infections, which is found in parts of South East Asia).

How can malaria be prevented?

Antimalarial treatments are thought to prevent 90% of malaria infections, but it should be noted that some people have adverse reactions to them. As a result, you may need to take a short course to see how well you tolerate these treatments before travelling to a country where malaria is a risk.

How is malaria diagnosed?

Diagnosis requires a simple blood test and treatment can then begin immediately. The same medication to prevent malaria can be used to treat it, but you will need to use a different medication than the one you used to prevent it if it wasn’t effective. 

The specific medication you will be prescribed and its strength will depend on a number of things, such as where you were infected, the type of malaria you have, how severe your symptoms are, your age and whether you are pregnant. Usually treatment is available in tablet or capsule form, but in the case of severe infections, an intravenous drip may be required.

If you are diagnosed with malaria, as long as you are treated for it promptly, it’s likely that you will make a full recovery. 

What is trichomoniasis?

Trichomoniasis is a sexually transmitted infection related to the parasite trichomonas vaginalis (TV). It can be treated effectively with medication but is unlikely to clear up by itself. It can present without symptoms, so if you are unsure as to whether you have the infection, you should make an appointment with your GP or sexual health (GUM) clinic. 

What symptoms does trichomoniasis cause?

Noticeable symptoms appear in about half of all cases and will likely occur within one month of the original infection. You are infectious whether it presents with or without symptoms.

Symptoms of trichomoniasis are similar to other sexually transmitted diseases, and as such can be difficult to diagnose. In women, indications include foul smelling discharge that appears thick and frothy, and it may be green in colour. You may also experience soreness of the vagina and itchiness inside of the thighs. Urination and sexual activity may be noticeably painful. 

In men, pain when urinating or ejaculating is likely to occur, and an increased urge to urinate more often. White discharge and soreness of the penis and foreskin are other common symptoms of the infection.

How is trichomoniasis treated?

Treatment for trichomoniasis is a straightforward course of antibiotics and antiprotozoals, most likely metronidazole. It should be taken for five to seven days, typically twice a day, although it may be prescribed as a single-use, high dosage pill. It should be noted that you are more likely to experience side effects if it’s taken as a one-off tablet. 

Once you have finished this course of treatment, a follow-up appointment can be made to see if the infection has cleared up. If you have followed the instructions correctly, another course of treatment is unlikely to be required. You should avoid having sex until seven days after the treatment has finished to ensure that reinfection does not occur. 

How can trichomoniasis be prevented?

The best method of reducing the risks involved with any sexually transmitted infection is to wear a condom during sex. Not only will this help to protect you against trichomoniasis, but also chlamydia, HIV, gonorrhoea and other infections. 

If you are sexually active, you should ensure you have regular health check-ups as many infections, including trichomoniasis, do not always present with symptoms immediately. Failure to diagnose a sexually transmitted infection can lead to certain health complications, such as infertility, as well as carry the risk of passing on infections to others.

What is giardiasis?

Giardiasis is an infection of the stomach that is usually caused by drinking infected water (as happens in many developing countries), ingesting food or drink prepared by someone who is infected and having unprotected sex (most commonly anal sex). When treated, the infection should pass within about a week, but some infections can be prolonged.

Symptoms of giardiasis include diarrhoea, stomach cramps, bloating, burping, flatulence and weight loss. It is also possible to be infected and not have any noticeable symptoms while passing the condition on to others. 

How is giardiasis diagnosed?

Diagnosis of giardiasis requires a stool test, and it’s possible that the people you live with will need to be tested to rule out the possibility that they are carrying the parasite. The most infectious time is likely as soon as symptoms present until two days after they have subsided. 

A course of antibiotics and antiprotozoals can help to clear up the infection within a matter of a few days, and symptoms should dissipate after about one week, but it is possible that they will persist for longer. During this time, you should make sure to consume lots of liquids, preferably water, as you are likely to become dehydrated due to the diarrhoea. You should also wash your hands regularly, as well as any bedding, on a hot wash. Cleaning toilets, handles and surfaces will also help to prevent infections from spreading.

If you have any questions or concerns related to the conditions described above or antiprotozoals, our GPhC-registered clinicians are available to speak to via our online video consultation service. You can book an appointment with them from 9.30am-4.30pm, Monday to Friday. They can also issue fit notes and referral to specialists for treatment, where appropriate.  

Page last reviewed:  25/06/2020
Side effects and warnings

What side effects do antiprotozoals have?

While most people will be able to tolerate these medications without many issues, in some cases there can be side effects. It’s not possible to know in advance who is likely to experience issues with any medication, so it’s important that you understand what side effects are possible, including the rarer and more serious ones. Your prescribing doctor will be able to inform you of the risks involved, and you can always refer to the patient information leaflet that comes with your medication, which lists all known side effects and their frequency.

Because antiprotozoals come in different forms, the following information may not relate to your specific treatment. The side effects that are listed below are associated with the antiprotozoal metronidazole.

If you experience any of the following, discontinue use and seek immediate medical attention: swelling of the hands, feet, ankles, face, lips or throat, itchy, lumpy rash hives, urticaria, fever, stiff neck, headache, hallucinations, problems using your arms and legs, problems speaking, confusion, Stevens-Johnson syndrome, toxic epidermal necrolysis, reddish target-like spots, circular patches often with central blisters on the trunk, skin peeling, ulcers of the mouth, throat, nose, genitals and eyes, preceded by fever and flu-like symptoms, a red, scaly widespread rash with bumps under the skin, blisters, yellowing of the skin and eyes, jaundice, infections, mouth ulcers, bruising, bleeding gums, severe tiredness, severe stomach pain and pancreatitis.

Other symptoms include: 

Very rare (affects less than 1 in 10 000 people): fits, feeling confused, hallucinations, blurred or double vision, skin rashes, flushing, headaches, darkening of the urine, feeling sleepy, dizziness, pains in the muscles or joints and liver problems. 

The following side effects have been reported but there is not enough data to suggest their frequency: numbness, tingling, pain, weakness in the arms or legs, unpleasant taste in the mouth, furred tongue, nausea, vomiting, upset stomach, stomach pain, diarrhoea, loss of appetite, fever, depression, optic neuritis, fever, nausea, vomiting, headache, stiff neck, extreme sensitivity to light, meningitis, hearing impairment, hearing loss, tinnitus and a rash or skin discolouration.

Is it safe to use antiprotozoals with other treatments?

All drugs have the potential to interact with other substances when taken alongside each other, so it’s essential that you tell your doctor about any other treatment you are using before starting a course of treatment with antiprotozoals. This includes herbal treatments and supplements. 

The following information relates to the antiprotozoal metronidazole, which may not be suitable for you if you are taking any of the following: blood thinners, lithium, phenobarbital, phenytoin, 5 fluorouracil, busulfan for leukaemia, ciclosporin and disulfiram for alcoholism.

Warnings and precautions for using antiprotozoals

If you suffer from any other health conditions, it’s important that you inform your prescribing clinician, so they can prescribe antiprotozoals safely. This includes any conditions you are prone to. 

The following information relates to the antiprotozoal metronidazole. Do not take it if you are allergic to any of its ingredients. Please inform your doctor of any allergies you are known to have. The ingredients in metronidazole can be found in the patient information leaflet that comes with the treatment.

Your doctor may consider metronidazole unsuitable if you are suffering for any of the following: liver problems, you are on kidney dialysis, you have have diseases of the nervous system,  you have Cockayne syndrome, you have Stevens-Johnson syndrome (SJS), you have toxic epidermal necrolysis (TEN) and acute generalised exanthematous pustulosis (AGEP).

If you are concerned about having an allergic reaction to any other antiprotozoals, you should consult your prescribing clinician, and read the patient information leaflet enclosed with your medication. 

Is it safe to take antiprotozoals if you are pregnant?

Unless your doctor considers it absolutely necessary, many antiprotozoals should not be taken whilst you are pregnant. 

It’s important that you tell your prescribing clinician if you are pregnant or think you might be pregnant before starting treatment. Trace amounts of antiprotozoals can be passed on to the baby through breastmilk, so it’s not recommended that you take these treatments while you are breastfeeding.

Is it safe to consume alcohol whilst taking antiprotozoals?

You should avoid consuming alcohol whilst using antiprotozoals as it can produce unpleasant side effects. These include stomach pains, nausea, vomiting, headaches, flushes and palpitations.

What types of antiprotozoals are available?

There are two classes of antiprotozoals: antimalarials and treatments used for other infections. Antimalarials include mefloquine, chloroquine, proguanil, atovaquone and doxycycline. These drugs can be used in both the prevention and treatment of the condition. 

Other types of antiprotozoals (which are used to treat trichomoniasis and giardiasis for example) include metronidazole, nifuratel and tinidazole.

Do I need to undergo any tests during treatment with antiprotozoals?

If you are taking these medications for longer than ten days, your prescribing doctor will likely want to run some tests to ensure that they’re safe for you to continue to use.


Page last reviewed:  25/06/2020
Questions and Answers

Will antiprotozoals affect my ability to drive?

Side effects related to antiprotozoals include hallucinations, dizziness, fits and issues with your vision. Although most of these side effects are rare, it’s important to understand their risks and avoid operating any form of heavy machinery if they occur. 

Can I buy antiprotozoals over the counter? 

No. Antiprotozoals are prescription-only treatments. 

How can I buy antiprotozoals online?

If you would like to speak to a GMC-registered clinician about antiprotozoals and any related conditions, you can make an appointment using our online video consultation service. Our clinicians are available from 9.30am-4.30pm, five days a week. They can also provide referral to specialists for treatment and fit notes, where suitable.  


Page last reviewed:  25/06/2020

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