What is Trimethoprim?
Trimethoprim is an antibiotic used to treat urinary tract infections. It selectively inhibits a bacterial enzyme and thereby has a bacteriostatic to bactericidal effect.
The medication concentrates in the urine, where it reaches high concentrations. For uncomplicated bladder infections, a 3-day course of therapy is usually sufficient.
Trimethoprim can also be used in combination with sulfamethoxazole (co-trimoxazole), but for urinary tract infections, trimethoprim alone is sufficient.
Active Ingredients & Mechanism of Action
Active ingredient: Trimethoprim
Trimethoprim inhibits bacterial folic acid synthesis:
Mechanism of action:
- Inhibits the enzyme dihydrofolate reductase (DHFR)
- Blocks the synthesis of tetrahydrofolic acid
- Without tetrahydrofolic acid, bacteria cannot produce DNA building blocks
- Bacterial growth is inhibited
Selectivity: Trimethoprim inhibits bacterial DHFR about 50,000 times more strongly than human DHFR. It therefore acts specifically against bacteria.
Spectrum of activity:
- E. coli (the most common cause of urinary tract infections)
- Klebsiella
- Proteus mirabilis
- Staphylococcus saprophyticus
- Enterobacter
Who is it suitable for?
Trimethoprim is suitable for:
- Uncomplicated urinary tract infections (cystitis)
- Prophylaxis of recurrent urinary tract infections
Advantages:
- Simple dosing (2x daily)
- Short treatment duration (3 days)
- Good tolerability
Not suitable in cases of:
- Pyelonephritis
- Complicated urinary tract infections
- Pregnancy
- Folic acid deficiency
- Severe kidney impairment
Available Dosages
Acute bladder infection:
- 200 mg 2x daily for 3 days
Prophylaxis:
- 100 mg in the evening over several months
Available strengths:
- Tablets 100 mg, 200 mg
In kidney impairment: Dose reduction required.
Dosage form and pack sizes
The medicines catalogue lists 2 pack variants: 2 strengths in 2 pack sizes. Pack sizes range from 10 to 20 units.
- Dosage form
- Tablette
- Strengths
- 100 mg, 200 mg
- Pack sizes
- 20 units, 10 units
| Strength | Pack | PZN | Duration |
|---|---|---|---|
| 100 mg | 20 units | 02736047 | 0 days |
| 200 mg | 10 units | 02736136 | 0 days |
Packs listed in the German medicines catalogue. Which of them are currently available and what they cost is shown in the price overview.
The Pharmazentralnummer (PZN) is the nationwide unique identifier of a pack in Germany.
Duration is the catalogue value for the usual dosage. How long a pack actually lasts depends on the dose your doctor prescribes.
How to Take
How to take:
- With or after a meal
- With plenty of water
- Take the two daily doses about 12 hours apart
Treatment duration:
- 3 days for acute bladder infection
- Finish the entire pack
- Do not stop early
Prophylaxis:
- In the evening before going to bed
- Possible over several months
- Under medical supervision
Notes:
- Drink plenty of fluids during treatment
- Symptoms usually improve after 1-2 days
- See a doctor if symptoms worsen or if you have a fever
Contraindications
Trimethoprim must not be taken in cases of:
- Hypersensitivity to trimethoprim
- Pregnancy (especially 1st trimester – folic acid antagonist)
- Breastfeeding
- Severe liver impairment
- Megaloblastic anemia due to folic acid deficiency
- Blood formation disorders
- Severe kidney impairment (creatinine clearance below 10 ml/min/1.73 m²)
Caution in cases of:
- Kidney impairment (dose adjustment)
- Folic acid deficiency
- Elderly patients
- Use of potassium supplements (risk of hyperkalemia)
Possible Side Effects
Common (1-10%):
- Nausea
- Vomiting
- Diarrhea
- Skin rash
- Itching
Uncommon:
- Headache
- Changes in blood count
- Elevated potassium in the blood
Rare:
- Megaloblastic anemia (with prolonged use)
- Severe skin reactions
- Liver damage
Note: With short-term use (3 days), serious side effects are rare.
Interactions
Interactions:
- Methotrexate – increased toxicity (both inhibit folic acid metabolism)
- ACE inhibitors, potassium-sparing diuretics – risk of hyperkalemia
- Warfarin – increased tendency to bleed
- Phenytoin – increased levels
Caution with:
- Folic acid antagonists
- Medications that affect the blood count
Recommendation: If you are taking methotrexate or potassium: inform your doctor.
Frequently Asked Questions
For an uncomplicated bladder infection, yes.
Trimethoprim is a folic acid antagonist. Folic acid is important for the development of the child. Especially in the 1st trimester, trimethoprim can cause birth defects.
Co-trimoxazole contains trimethoprim plus sulfamethoxazole. For uncomplicated urinary tract infections, trimethoprim alone is sufficient.
With caution and at a reduced dose. In severe kidney impairment, trimethoprim is contraindicated. Inform your doctor about your kidney function.
Similar Medications
Is Trimethoprim right for you?
A licensed doctor will review your information and issue a prescription if suitable. Discreet and secure.
Important Notice
This information does not replace medical advice. If you have questions about your health or the suitability of this medication, please consult a doctor or pharmacist.
Important Safety Information
This service operates under German pharmaceutical law (HWG). For risks and side effects, read the package leaflet and consult your doctor or pharmacist. All medications are dispensed from a licensed pharmacy in Germany.