Trimethoprim

Question 1

Trimethoprim - indications

Answer 1

Acute lower UTI

Prophylaxis for recurrent lower UTI
- alternatives are nitrofurantoin, amoxicillin, cefalexin

Question 2

Trimethoprim - MOA

Answer 2

Bacteria make their own folate for essential functions such as DNA synthesis

Trimethoprim acts by inhibiting bacterial folate synthesis and therefore slowing bacterial growth

Bacteria can overcome this mechanism = widespread bacterial resistance

Question 3

Trimethoprim - adverse effects

Answer 3

Most common
1) GI upset - nausea, vomiting, sore mouth

2) skin rash

Others
3) hyperkalaemia

4) haematological disorders - megaloblastic anaemia, leucopenia and thrombocytopenia

Rare
5) hypersensitivity reactions - anaphylaxis, drug fever, erythema

Question 4

Trimethoprim - contraindications (avoid)

Answer 4

first trimester of pregnancy

Question 5

Trimethoprim - Contraindications ( use with caution in…)

Answer 5

folate deficiency

renal impairment

neonates

elderly

HIV

Question 6

Trimethoprim - interactions

Answer 6

K+ elevating drugs (e.g.- aldosterone antagonists, ACEi/ARBs)

folate antagonist (e.g.- methotrexate)

drugs that increase folate metabolism (e.g.- phenytoin)

warfarin - can enhance anticoagulant effect