A Comprehensive Guide to Understanding and Using Trimethoprim
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Order Trimethoprim →What Is Trimethoprim?
Trimethoprim is a commonly prescribed antibiotic in the UK, primarily used to treat urinary tract infections (UTIs). It belongs to a class of antibiotics known as dihydrofolate reductase inhibitors — it works by disrupting the bacteria’s ability to produce folic acid, a vital nutrient for their growth and survival. By blocking this process, trimethoprim prevents bacteria from multiplying and allows the body’s immune system to clear the infection.
Trimethoprim is available from Access Doctor as 200mg tablets following a GPhC-regulated online consultation.
What Infections Does Trimethoprim Treat?
Trimethoprim is primarily prescribed for:
- UTIs and cystitis — bladder and kidney infections. NICE second-line recommendation after nitrofurantoin
- Chest infections — certain respiratory bacterial infections
- Acne — used long-term at lower doses for inflammatory acne
- Ear, nose, and throat infections — occasional use for bacterial ENT infections
- Traveller’s diarrhoea — some bacterial causes respond to trimethoprim
Trimethoprim is not effective against viral infections — including colds, flu, or COVID-19. It should only be used when a bacterial infection has been confirmed or strongly suspected by a healthcare professional.
How Does Trimethoprim Work?
Trimethoprim inhibits the enzyme dihydrofolate reductase, which bacteria need to convert dihydrofolic acid into tetrahydrofolic acid — the active form of folate required for DNA synthesis. Without this process, bacteria cannot replicate their genetic material and are unable to multiply. The body’s immune cells can then successfully eliminate the static bacterial population.
How to Take Trimethoprim
- Standard adult dose for UTI: 200mg twice daily (one tablet morning, one tablet evening)
- Course length: Typically 7 days for UTIs — follow your prescriber’s specific instructions
- How to take: Swallow tablets whole with a glass of water. Can be taken with or without food.
- Timing: Take at the same time(s) each day to maintain consistent blood levels
- Complete the course: Always finish all prescribed tablets — even if you feel better earlier
Side Effects of Trimethoprim
Common side effects (usually mild and temporary):
- Nausea and vomiting
- Diarrhoea
- Skin rash or itching
- Headache and dizziness
For a comprehensive guide to trimethoprim side effects — including rare but serious effects and long-term considerations — see: Trimethoprim Side Effects: Your Questions Answered.
Seek immediate medical attention if you experience: severe allergic reaction (difficulty breathing, swelling of face/lips/throat); unusual bruising or bleeding; high fever with sore throat; muscle weakness or irregular heartbeat; yellowing of skin or eyes (jaundice).
Important Considerations
Before being prescribed trimethoprim through Access Doctor, you will complete a confidential online consultation. It is important to disclose:
- Any known allergies to trimethoprim or other antibiotics
- Liver or kidney problems
- Anaemia or low folic acid levels
- Porphyria or blood disorders
- Pregnancy or breastfeeding status (first trimester — avoid; second/third — discuss)
- All other medications, including over-the-counter and herbal supplements
Common Questions Answered
Can I drink alcohol while taking trimethoprim?
Yes — unlike metronidazole, trimethoprim does not cause a dangerous reaction with alcohol. Drinking in moderation is acceptable. However, excessive alcohol can weaken your immune system and potentially slow recovery. Moderate consumption is advisable.
What if I miss a dose?
Take the missed dose as soon as you remember — unless your next dose is imminent. In that case, skip the missed dose and continue your regular schedule. Never take a double dose to compensate for a missed one. Setting a daily phone alarm helps maintain consistency.
Can I take trimethoprim if I’m pregnant?
Trimethoprim should generally be avoided in the first trimester as it interferes with folate metabolism, which is critical for foetal development. It may be used in the second and third trimesters when clinically necessary. Discuss your circumstances with your prescriber.
Getting Trimethoprim from Access Doctor
Access Doctor provides a convenient alternative to GP appointments for qualifying UTI treatment. Complete a GPhC-regulated online consultation — our qualified prescribers will assess whether trimethoprim is appropriate for your specific needs. Once approved, trimethoprim is delivered directly to you in discreet packaging. We offer a range of delivery options through Royal Mail to suit your convenience.
💊 NICE First-Line Antibiotic
Nitrofurantoin (Macrobid)
MHRA-approved first-line antibiotic for cystitis & UTIs. Prescription via GPhC-regulated online consultation.
Order Nitrofurantoin →💊 Prescription Antibiotic
Trimethoprim
MHRA-approved alternative antibiotic for cystitis. Suitable where nitrofurantoin is not appropriate.
Order Trimethoprim →Order Trimethoprim — No GP Appointment Needed
Our GPhC-registered pharmacist independent prescribers review your consultation and prescribe the right UTI antibiotic for your circumstances. Discreet next-day delivery.
Treat Cystitis Online →Frequently Asked Questions About Trimethoprim
What is trimethoprim used for?
Trimethoprim is primarily for UTIs including cystitis and kidney infections. It can also treat some chest infections, acne, ear/nose/throat infections, and traveller’s diarrhoea. It is NICE second-line for uncomplicated UTIs after nitrofurantoin.
How does trimethoprim prevent bacterial infection?
Trimethoprim blocks the enzyme dihydrofolate reductase, which bacteria need to produce folic acid for DNA synthesis. Without folic acid, bacteria cannot replicate — allowing the immune system to clear the infection.
Is trimethoprim effective against viral infections?
No — trimethoprim only treats bacterial infections. It is ineffective against viral conditions including colds, flu, and COVID-19. It should only be taken when prescribed for a confirmed bacterial infection.
What should I do if trimethoprim causes side effects?
For mild effects (nausea, rash, diarrhoea), inform your prescriber — they can advise on continuing or adjusting treatment. For severe effects (difficulty breathing, unusual bruising, high fever with sore throat), seek immediate medical attention.
Can I drink alcohol while taking trimethoprim?
Yes, in moderation. Trimethoprim does not cause the dangerous reaction with alcohol that metronidazole does. However, excessive alcohol can weaken immunity — moderate consumption is advisable during treatment.
Is trimethoprim available without a prescription?
No — trimethoprim is prescription-only in the UK. Access Doctor’s GPhC-regulated online consultation allows you to obtain it without a traditional GP appointment, with delivery directly to your door.
References
- NICE. Urinary tract infection (lower) — women. Clinical Knowledge Summaries. Available at: cks.nice.org.uk/topics/urinary-tract-infection-lower-women
- NHS. Cystitis. Available at: nhs.uk/conditions/cystitis
- UKHSA. English surveillance programme for antimicrobial utilisation and resistance (ESPAUR). Available at: gov.uk
- Electronic Medicines Compendium. Nitrofurantoin 100mg m/r capsules — SmPC. Available at: medicines.org.uk/emc
- Electronic Medicines Compendium. Trimethoprim 200mg tablets — SmPC. Available at: medicines.org.uk/emc
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. Nitrofurantoin and trimethoprim are prescription-only medicines — a medical consultation is required before they can be dispensed. If you have a fever, loin/back pain, or are pregnant, seek urgent in-person medical care. In an emergency, call 999.