Trimethoprim

Question 1

What is trimethoprim used for?

Answer 1

Trimethoprim is used as a first line treatment for UTIs.

Question 2

What is Co-trimoxazole and what is it used for?

Answer 2

Co-trimoxazole is trimethoprim + sulfamethoxazole . It is used to treat pneumocystitis pneumonia in immune-suppressed pt.

Question 3

How does trimethoprim work?

Answer 3

Trimethoprim inhibits bacterial folate synthesis. so bacteria cant make DNA. This slows their growth.

Question 4

What bacteria does trimethoprim work against?

Answer 4

Gram positive, gram negative bacteria
enterobacteria e.g. E.coli

HOWEVER WIDESPREAD RESISTANCE so usage is limited

Question 5

What are the side effects of trimethoprim/

Answer 5

• GI upset (nausea, vomiting, sore mouth)
• Skin rash
• anaphylaxis (rare)
• haematological disorders e.g. megaloblastic anaemia, leucopenia, thrombocytopenia
• hyperkalaemia
• elevated plasma creatinine concentration

Question 6

Why is trimethoprim contraindicated in the 1st trimester of pregnancy?

Answer 6

trimethoprim is a folate antagonist so is associated with increased risk of fetal abnormalities

Question 7

What groups of patients are particularly susceptible to adverse affects with trimethoprim?

Answer 7

• neonates
• elderly
• HIV infection

Question 8

What are the interactions of trimethoprim?

Answer 8

• potassium elevating drugs ( e.g. aldosterone antagonist, ACEi, angiotensin receptor blocker)
• use with folate antagonists e.g. methotrexate
• drugs that increase folate metabolism e.g.phenytoin
• warfarin