Trimethoprim is a form of medication belonging to the family called “antibiotics”. Antibiotics like Trimethoprim work to treat bacterial infections, they will not work for viral infections such as the flu or the common cold. More information

A doctor will review your order and write you a prescription, if appropriate. This prescription is then forwarded to a pharmacy. The pharmacy will have your medicine delivered to you within one to three working days. Read more about this process here.

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Trimethoprim is a type of antibiotic used for the treatment of bacterial infections. This medication works by interfering with the way that bacteria in your body can product proteins that are essential for their growth. Trimethoprim is a prescription only medication.  

What is Trimethoprim? 

Trimethoprim is a form of medication belonging to the family called “antibiotics”. Antibiotics like Trimethoprim work to treat bacterial infections, they will not work for viral infections such as the flu or the common cold. Before taking this medication or any other, it’s important to remember that taking antibiotics when they’re not needed can lead to you becoming resistant to the medication.  

Many people taking Trimethoprim will improve within a few days of starting their treatment. If your symptoms do not improve even though you’re taking your tablets routinely, then you should contact a doctor. You might need a different kind of antibiotic. Certain UTI bacteria may be resistant to Trimethoprim.  

When is Trimethoprim used? 

Trimethoprim is a specific form of antibiotic given to treat bacterial infections. This medication is most often given to people suffering from urine infections. However, you may be given Trimethoprim if you are having a chest infection too. This drug kills the bacteria in your body responsible for causing the infection and the symptoms, such as pain and discomfort.  

UTIs, or urinary tract infections are often caused by bacteria that come from your own bowel. These infections are often more common in women than in men, simply because of the structure of the female body. Usually, UTIs are very easily treated with a short course of an antibiotic like Trimethoprim. However, you might need a longer course of antibiotics, or a different kind of treatment depending on your condition.  

Trimethoprim is only available when provided with a prescription, after a full consultation.  

How do you use Trimethoprim? 

Trimethoprim is typically given in tablet form. You’ll be able to take it by mouth either with or without food depending on your consultant’s instructions. Sometimes, taking medications with food can make them less likely to cause gastrointestinal side effects like nausea or sickness.  

Make sure that you read the patient leaflet included with these tablets before you begin taking them. Your leaflet will provide you with more information about how the medication works, as well as how you might be able to avoid side effects. If you are using the liquid form of this medication, make sure that you always measure your dose using the special measuring device provided.  

Trimethoprim works best when it is taken at evenly spaced times. If you’re worried about remembering to take your medication, try to take it at the same time each day. You must continue to take Trimethoprim until you have completed your full course. Continue to take this medication even if your condition appears to have improved and your symptoms disappear. Stopping a course of antibiotics too early can cause an infection to return.  

What dosages are there? 

Trimethoprim is available in a multitude of different strengths, including tablets designed to prevent recurrent urinary infections. Usually, you will need to take this medication once or twice daily for a specific period of time. The dosage you are given, and the length of your treatment will be based on a number of factors, including the nature of your infection.  

The most common dosage for adults and children over the age of 12 is 200mg of Trimethoprim taken twice each day. If your infection is particularly bad, then you might need to take a higher dose, or continue your treatment for longer.  

Tell your doctor if your condition doesn’t get better or worsens after using this medication for a few days.  

What are the side effects of Trimethoprim? 

All medications can cause side effects, as well as their intended effects. Sometimes, the side effects associated with Trimethoprim will disappear on their own, often after your body has gotten used to the medication. The most common side effects of Trimethoprim are vomiting, nausea, Diarrhea, sickness, and stomach upset. You might find that you have less of an appetite than usual when taking these pills. Additionally, some people report headaches and changes in taste.  

If you find that any of the common side effects of Trimethoprim persist or get worse over a period of several days, contact a pharmacist or doctor. Remember that you should seek immediate assistance if you notice any more severe side effects from this medication, including: 

New signs of an infection, including a sore throat or fever; 

  • Easy bruising or bleeding; 
  • Paler than usual skin; 
  • Unusual tiredness or fatigue; 
  • Irregular or fast heartbeat; 
  • Muscle weakness; 
  • Stiff neck and headache; 
  • Extreme drowsiness; 
  • Signs of low blood sugar like hunger, dizziness or blurred vision. 

In very rare conditions, this medication can cause a significant intestinal condition called clostridium-difficile diarrhea. This condition is caused by the presence of a very resistant bacteria in your gut. The condition can take place months or weeks after you have already finished your treatment with Trimethoprim. Tell your doctor if you develop severe diarrhea, stomach pain and cramping, mucus or blood in your stool, or any other severe symptoms. If you do have this condition, do not use opioid medications or anti-diarrhea pills, as they can make your situation worse. 

Using Trimethoprim for extended periods of time can lead to yeast infections and oral thrush. Consult a doctor if you notice patches of white skin in your mouth or changes in your vaginal discharge. Get help immediately if you have serious side effects after taking Trimethoprim, like seizures.  

Serious allergic reactions to Trimethoprim are rare, but it is important that you are aware of the signs of an allergic reaction, including rashes and itching or swelling around the throat, tongue and face. You should contact an emergency care facility immediately if you have trouble breathing.  

When shouldn't you use Trimethoprim? 

Some people will not respond well to Trimethoprim. It is important to answer any questions your consultant has about your condition and medical history truthfully to ensure that this substance is suitable for you. Before taking Trimethoprim, make sure that you tell your consultant whether you are allergic to any similar antibiotics, or inactive ingredients that may be found in these drugs.  

Before using Trimethoprim, make sure that your consultant is aware of your medical history, particularly if you have a history of a type of anemia caused by folate deficiency. You should not take Trimethoprim if you have had kidney or liver disease, or you have a vitamin deficiency for folate. Blood disorders and bone marrow suppression issues can make this medication more dangerous. Mineral imbalances such as a higher than usual level of potassium or less sodium in your blood may make you unsuitable for this medication.  

Trimethoprim and similar medications can sometimes make you more sensitive to sunlight. Ensure that you limit your time in the sun when using these pills and avoid sunlamps or tanning booths. Use sunscreen and wear plenty of protective clothing when you’re outdoors. Remember to tell your doctor immediately if you get any blisters or redness on your skin.  

If you have diabetes, then it is important to note that Trimethoprim can affect your blood sugar. You will need to check your blood sugar levels regularly to make sure that you are not dropping too low or going too high. Share your results with your doctor, and make sure that you inform a health practitioner immediately if you see signs of low blood sugar.  

Keep in mind that Trimethoprim can cause some vaccines with live bacteria to be less effective. It is not a good idea to have any vaccinations or immunizations when you are using this medication unless you have approval to do so. Before you have surgery, you should also let your doctor or surgeon know that you are taking this drug.  

Trimethoprim should not be taken by any women planning on becoming pregnant, or by women who are already pregnant. Trimethoprim could be harmful to your unborn baby and cause an increased risk of spinal cord issues. Make sure that you check with your doctor to ensure that you are taking enough folic acid when you are pregnant and talk to your doctor about the potential risks of this medication for pregnancy.  

Does Trimethoprim interact with any other medications? 

Trimethoprim can sometimes interact negatively with other medications that you may already be taking. An interaction could change how your medication works or increase your chances of serious side effects. You will need to ensure that your consultant is aware of any other medications that you are taking when you apply for this medication. Remember to tell your consultant about prescription medications, over-the-counter drugs and herbal supplements.  

Though most antibiotics will not affect the way that the hormonal contraceptive pill, patch, or ring works, some antibiotics can decrease their effectiveness. Speak to your consultant about whether you need to use any additional forms of contraception when you are using Trimethoprim.  

Where can you buy Trimethoprim? 

Trimethoprim is available from collaborating pharmacies. You will be able to place an order for Trimethoprim with Dokteronline and complete a consultation with one of our EU professionals. A prescription can be sent to you to a corresponding pharmacy for the medication of your choice.  

Can you get Trimethoprim without a prescription?  

Before taking any antibiotics, you must consult your doctor face to face. Most antibiotics, including Trimethoprim will not be available without a prescription. You will need to have a full consultation before getting this medication.  


BNF Nice, online, 2019, “Trimethoprim”, [Accessed 20th of November 2019] Available on:, online, 2019 “Trimethoprim”  [Accessed 20th of November 2019] Available on: 

NHS, online 2019, “Trimethoprim” [Accessed 20th of November 2019] Available on: 

Assessed by:

Dr Imran Malik, General practitioner
Registration number: GMC: 4741365

Dr Imran Malik studied undergraduate medicine at King's College University in Central London and clinical studies at the prestigious King's College Hospital. He graduated with a MBBS degree in 2000 and went on to gain postgraduate memberships with the Royal Society of Medicine and also General Practice in 2006.