Trimethoprim Tablets

What is Trimethoprim and How Does It Work Against Bacteria?

Trimethoprim is a bacteriostatic antibiotic, meaning it stops bacteria from growing and multiplying. It is classified as a broad-spectrum agent, making it effective against a wide range of bacteria, particularly those that commonly infect the urinary tract, such as Escherichia coli (E. coli).

Its mechanism of action is highly specific. Bacteria need folate (a B vitamin) to produce DNA and replicate. Unlike humans who get folate from their diet, bacteria must synthesise it themselves. Trimethoprim works by precisely inhibiting a bacterial enzyme called dihydrofolate reductase. This blockade disrupts the production of tetrahydrofolate, a crucial component in the folate synthesis pathway. Without this, the bacteria cannot produce genetic material and essential proteins, effectively halting their growth and leading to their eventual death. This targeted approach makes it a valuable tool in fighting uncomplicated urinary tract infections.

Crucial Information Before You Start Taking Trimethoprim

To ensure your safety, it is vital to discuss your full medical history with your doctor. Do not take Trimethoprim and inform your doctor immediately if any of the following apply to you:

• Allergy: You are allergic to trimethoprim or any of the other ingredients listed in this leaflet (see section 6).
• Blood Disorders: You have any known blood disorder (e.g., anaemia).
• Pregnancy: You are pregnant or trying to become pregnant. Trimethoprim is not recommended during pregnancy.
• Severe Liver Disease: You have severe liver problems.
• Newborns: It should not be given to premature babies or newborns in their first few weeks of life.

Warnings and Precautions for Trimethoprim Use

Talk to your doctor or pharmacist before taking Trimethoprim if you have:

• Kidney Disease: Impaired kidney function may require a dose adjustment.
• Folate Deficiency: A pre-existing deficiency of folic acid may be exacerbated, potentially leading to anaemia.
• Diabetes: Particularly if poorly controlled.

Important Note on Potassium: Trimethoprim can increase potassium levels in the blood (hyperkalaemia). This risk is higher in patients with kidney problems, poorly controlled diabetes, or those taking certain medications like potassium-sparing diuretics or ACE inhibitors. Symptoms of high potassium can include muscle cramps, irregular heartbeat, nausea, and dizziness. Your doctor may monitor your potassium levels with blood tests during treatment.

Other Medicines and Trimethoprim Interactions

Always inform your doctor of all medicines you are taking, including over-the-counter drugs and herbal remedies. Key interactions include:

• Warfarin: Trimethoprim may enhance the blood-thinning effect of warfarin, increasing the risk of bleeding.
• Phenytoin: Levels of this epilepsy medication may be increased by Trimethoprim.
• Methotrexate: The risk of blood disorders may be increased when taken with Trimethoprim.
• ACE Inhibitors/Angiotensin II Receptor Blockers (ARBs): (e.g., Ramipril, Losartan) can increase the risk of high potassium levels.
• Diuretics: Specific diuretics like spironolactone, amiloride, or triamterene also increase potassium and should be used with caution.
• Digoxin: Used for heart conditions, its levels may be affected.
• Repaglinide: (A diabetes medicine) - its effect may be enhanced.

This is not an exhaustive list. Always check with your doctor or pharmacist before combining medicines.

Pregnancy, Breast-feeding, and Lactose Intolerance

Pregnancy: Trimethoprim is not recommended during pregnancy, especially in the first trimester, due to potential risks to the foetus.

Breast-feeding: Small amounts of Trimethoprim pass into breast milk. Consult your doctor for advice on whether to continue breastfeeding or stop taking the medicine.

Lactose: This medicine contains a small amount of lactose. If you have been told by your doctor that you have an intolerance to some sugars, contact your doctor before taking this medicine.

How to Take Trimethoprim for Effective Treatment

Always take this medicine exactly as your doctor has told you. The dose and duration will depend on the type and severity of your infection and your age.

1. Swallow the tablet whole with a glass of water.
2. It can be taken with or without food, as this does not affect its absorption.
3. Space your doses evenly throughout the day. For example, if you are taking it twice daily, take one dose in the morning and one in the evening.
4. Complete the full course of antibiotics, even if you start to feel better after a few days. Stopping early can allow the infection to return and contribute to antibiotic resistance.

What to Do If You Miss a Dose or Take Too Much Trimethoprim

If you forget to take a dose: Take it as soon as you remember, unless it is almost time for your next dose. In that case, skip the missed dose and continue with your regular schedule. Do not take a double dose to make up for a forgotten one.

If you accidentally take too much (overdose): Contact your doctor or go to the nearest hospital Accident and Emergency department immediately. Take the medicine pack with you so the medical staff can identify what you have taken.

Understanding the Potential Side Effects of Trimethoprim

Like all medicines, Trimethoprim can cause side effects, although not everybody gets them. It is important to be aware of them so you can seek medical advice if necessary.

STOP taking Trimethoprim and seek immediate medical help if you experience any signs of a severe allergic reaction:

• Difficulty breathing, wheezing, or swelling of the face, lips, tongue, or throat.
• Severe skin reactions like blistering, peeling, or a painful red rash.
• Chest pain, fainting, or collapse.
• Severe, persistent diarrhoea (which may be bloody) – this could be a sign of colitis.
• Sudden, severe abdominal pain (signs of pancreatitis).

Other Possible Side Effects

Common (May affect up to 1 in 10 people):

• Feeling sick (nausea) or being sick (vomiting)
• Diarrhoea
• Headache
• Skin rashes or itching (pruritus)
• Fungal infections like thrush

Uncommon to Rare:

• Increased potassium levels in the blood (hyperkalaemia)
• Anaemia, sore throat, or mouth ulcers (due to changes in blood cells)
• Dizziness, tiredness
• Liver function changes (may show as jaundice - yellowing of the skin/eyes)
• Depression, confusion, or sleep disturbances

This is not a complete list. For a full overview of side effects, please refer to the official Trimethoprim Patient Information Leaflet (PIL) on the medicines.org.uk website. If you get any side effects, talk to your doctor, pharmacist, or nurse. This includes any possible side effects not listed. You can also report side effects directly via the Yellow Card Scheme.

Detailed Trimethoprim Dosage Guidelines for All Ages

The following dosage information is a guide. Your doctor will determine the exact dose that is right for you.

Standard Treatment Dose for Infections

• Adults and children over 12 years: The usual dose is 200mg twice daily.
• Children aged 6 to 12 years: The usual dose is 100mg twice daily.
• Children under 6 years: A more suitable liquid formulation is usually recommended instead of tablets.

For severe or sudden infections, such as uncomplicated cystitis, treatment typically lasts between 3 to 14 days. Your doctor may instruct you to take a double dose (400mg) for your first dose to quickly achieve effective blood levels of the antibiotic.

Long-Term Prevention with Trimethoprim

For the prevention of recurrent UTIs, a much lower, single daily dose is used:

• Adults and children over 12 years: 100mg once daily, usually taken at night.
• Children aged 6 to 12 years: 50mg once daily at night.

Dosage in Elderly Patients and Those with Kidney Problems

Doses may be reduced in elderly patients or those with impaired kidney function. Your doctor will calculate the correct dose based on your kidney function test results.

Trimethoprim Interactions, Storage, and Composition

How to Store Your Trimethoprim Medication

• Keep this medicine out of the sight and reach of children.
• Store in a dry place below 25°C.
• Do not use this medicine after the expiry date printed on the carton and blister strip.
• Do not throw away medicines via wastewater or household waste. Return any unused medication to your pharmacy for safe disposal. This helps to protect the environment.

What is in Trimethoprim Tablets?

• The active substance is Trimethoprim. Each tablet contains 200mg of Trimethoprim.
• The other ingredients are Lactose monohydrate, Povidone K-25, Crospovidone, Sodium starch glycolate (Type A), and Magnesium stearate.

What the Tablets Look Like

Trimethoprim 200mg Tablets are white, flat, bevelled-edged tablets, engraved with 'MT200'. They are available in containers of 50, 100, 500, 1000, and 5000 tablets, or in blister packs of 6, 14, and 28 tablets.

Frequently Asked Questions About Trimethoprim

Clinical References and Sources

This content has been compiled using the manufacturer's Patient Information Leaflet (PIL) and information from authoritative UK health sources.

• NHS Trimethoprim Guide - Official NHS information on uses, key facts, and side effects.
• StatPearls Publishing - Detailed clinical information on Trimethoprim's mechanism and use.
• PMC Article on Antibiotic Use - Research on antibiotic prescribing and resistance.
• British Journal of General Practice - Historical and clinical context for Trimethoprim use.

Related Treatment Guides

Explore our other guides to learn more about managing urinary tract health.

• Nitrofurantoin for Cystitis: How It Compares
• Self-Care Tips for Preventing Recurrent UTIs
• Understanding Antibiotic Resistance in UTI Treatment

Where to Buy Trimethoprim in the UK