1. Introduction
Trimethoprim is a bacteriostatic antibiotic that inhibits dihydrofolate reductase, preventing bacterial DNA synthesis. It is primarily used to treat urinary tract infections (UTIs) and certain respiratory infections.
2. Indications
- Uncomplicated Urinary Tract Infections (UTIs)
- Acute & Chronic Prostatitis
- Respiratory Tract Infections (e.g., bronchitis)
- Pneumocystis jirovecii Pneumonia (PCP) (when combined with sulfamethoxazole)
- Shigellosis (Off-label Use, with sulfamethoxazole)
- Otitis Media (Middle Ear Infection) (Off-label Use)
3. Dosage
Adults:
- Uncomplicated UTI:
- 200 mg twice daily for 3–7 days (7 days if complicated or recurrent).
- Prostatitis:
- 200 mg twice daily for 4–6 weeks.
- Respiratory Infections (e.g., Bronchitis):
- 200 mg twice daily for 7–14 days.
- Pneumocystis jirovecii Pneumonia (PCP) (as part of co-trimoxazole):
- 15–20 mg/kg/day divided into 3–4 doses.
Children:
- UTI & Otitis Media:
- 3 mg/kg twice daily for 3–7 days.
Elderly:
- Use standard dosing but monitor renal function closely.
Renal Impairment:
- CrCl 15–30 mL/min: Reduce dose to 100 mg twice daily.
- CrCl <15 mL/min: Avoid use or use with caution.
Hepatic Impairment:
- Use with caution in severe hepatic disease.
4. Administration
- Take with or without food (if stomach upset occurs, take with food).
- Drink plenty of fluids to prevent crystalluria.
- Complete the full course even if symptoms improve.
5. Forms Available
- Tablets: 100 mg, 200 mg
- Oral Suspension: 50 mg/5 mL, 100 mg/5 mL
- IV Injection (as co-trimoxazole)
6. Side Effects
6.1 Common Side Effects:
- Nausea
- Vomiting
- Rash
- Loss of appetite
6.2 Less Common Side Effects:
- Itching (pruritus)
- Diarrhoea
- Headache
6.3 Rare but Serious Side Effects:
- Hyperkalaemia (high potassium levels)
- Megaloblastic Anaemia (due to folate deficiency)
- Stevens-Johnson Syndrome (SJS)
- Agranulocytosis (low white blood cells, increased infection risk)
7. Warnings
- Folate Deficiency Risk: Can cause megaloblastic anaemia, especially in malnourished or elderly patients.
- Hyperkalaemia: Can increase potassium levels, monitor in renal impairment.
- Hypersensitivity Reactions: Avoid if history of severe sulfa allergy (if used as co-trimoxazole).
- Blood Disorders: Risk of leucopenia, thrombocytopenia, or agranulocytosis in prolonged use.
8. Precautions
- Avoid in pregnancy, particularly in first trimester, due to risk of neural tube defects.
- Monitor potassium levels in elderly or patients on ACE inhibitors or spironolactone.
- Use with caution in patients with G6PD deficiency due to risk of haemolysis.
9. Interactions
- Methotrexate: Increased bone marrow suppression risk.
- Warfarin: Increased bleeding risk (monitor INR).
- ACE Inhibitors & Potassium-Sparing Diuretics: Increased risk of hyperkalaemia.
- Phenytoin: Increased phenytoin levels, leading to toxicity.
10. Monitoring Parameters
- Renal function (eGFR, creatinine levels).
- Potassium levels (to avoid hyperkalaemia).
- Complete blood count (CBC) in long-term therapy.
11. Use in Children
- Safe for paediatric UTI at appropriate doses.
- Not recommended in neonates (<2 months) due to risk of kernicterus.
12. Use in Pregnancy
- Category C:
- Avoid in first trimester (risk of neural tube defects).
- If essential, supplement with folic acid (5 mg daily).
13. Use in Elderly
- Increased risk of hyperkalaemia, renal impairment, and blood disorders.
- Monitor renal function and electrolytes.
14. Use in Kidney Disease
- Dose reduction required in moderate renal impairment.
- Avoid in severe renal failure (CrCl <15 mL/min).
15. Use in Liver Disease
- Use with caution in severe liver impairment due to metabolism in the liver.
16. Patient Counselling Points
- Take with plenty of water to prevent crystalluria.
- Complete the full course to avoid antibiotic resistance.
- Avoid excessive sun exposure, as it may increase sun sensitivity.
- Report any signs of allergic reaction (rash, swelling, fever).
- Monitor for unusual bleeding or bruising, which may indicate blood disorders.
17. Table of Brand Names, Manufacturer, and Prices in USD
Brand Name | Manufacturer | Strength/Dosage Form | Price (USD) |
---|---|---|---|
Proloprim | Various | 100 mg, 200 mg Tablet | $30 (30 tablets) |
Trimpex | Various | 50 mg/5 mL Oral Solution | $25 (100 mL) |
Generic Trimethoprim | Various | 100 mg, 200 mg Tablet | $10 (30 tablets) |
18. 15 FAQs (Frequently Asked Questions)
1. What is Trimethoprim used for?
It is used primarily for urinary tract infections (UTIs) and respiratory infections.
2. How does Trimethoprim work?
It inhibits dihydrofolate reductase, preventing bacterial DNA synthesis.
3. How long does Trimethoprim take to work?
Symptoms improve within 48–72 hours, but complete the full course.
4. Can I take Trimethoprim with food?
Yes, it can be taken with or without food.
5. Can Trimethoprim cause diarrhoea?
Yes, mild diarrhoea may occur; severe diarrhoea may indicate Clostridium difficile infection.
6. Can I drink alcohol while taking Trimethoprim?
Yes, but avoid excessive alcohol, as it may increase nausea.
7. Can pregnant women take Trimethoprim?
Avoid in the first trimester due to neural tube defect risk.
8. Does Trimethoprim cause sun sensitivity?
Yes, limit sun exposure and use sunscreen.
9. Can I take Trimethoprim with warfarin?
Use caution, as it can increase bleeding risk.
10. What should I do if I miss a dose?
Take it as soon as you remember, but do not double dose.
11. Does Trimethoprim cause allergic reactions?
Yes, rash, fever, or swelling may indicate an allergy.
12. Can I take Trimethoprim for a sore throat?
No, it is not effective against most sore throats (mainly viral infections).
13. Can Trimethoprim be used in children?
Yes, for paediatric UTIs and otitis media at adjusted doses.
14. Is Trimethoprim a penicillin?
No, it is a folate synthesis inhibitor, unrelated to penicillins.
15. How should Trimethoprim be stored?
Store at room temperature, away from moisture and heat.