Trimethoprim

Question 1

MoA

Answer 1

Inhibits bacterial folate synthesis, slowing bacterial growth.
Narrow-spectrum
Bactericidal

Question 2

Use + dose

Answer 2

UTI
Acute = 200 mg BD
Prophylaxis = 100 mg ON

Question 3

Side effects

Answer 3

Common = GI disturbances + stomach upset
Anti-folate (teratogenic in 1st trimester)
Blood dyscrasias (with long-term use)
- Counsel patients to report fever, sore throat, rash, mouth ulcers, purpura, bruising, bleeding
Hyperkalaemia

Question 4

Folate antagonist

Answer 4

Do not use in 1st trimester
Causes:
- Megoblastic anaemia
- Thromboyctopoenia
- Leucopoenia

Question 5

Interactions - hyperkalaemia

Answer 5

ACEi/ARB
Aldosterone antagonists

Question 6

Interactions (other anti-folates)

Answer 6

Methotrexate
Phenytoin (increases folate metabolism)

Question 7

Trimethoprim + warfarin

Answer 7

Enhances the anticoagulant effect of warfarin

Question 8

Co-trimoxazole

Answer 8

Trimethoprim/sulfamethoxazole
Used in prophylaxis + treatment of pneumocystis jirovecii pneumonia
Side effects:
- Rashes
- SJS
- Toxic epidermal necrolysis
- Photosensitivity