CLASSES OF ABX: TRIMETHOPRIM

Question 1

MOA

Answer 1

• Trimethoprim binds to and reversibly inhibits bacterial dihydrofolate reductase (DHFR) and blocks the production of tetrahydrofolate.

Question 2

Activity against

Answer 2

Gram +
Aerobic Gram -

including enterobacteria Escherichia coli, Klebsiella pneumoniae, Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus.

Question 3

indications

Answer 3

• Pneumonia
• Respiratory tract infections
• Shigellosis
• Invasive salmonella
• Urinary-tract infections
• Acne resistant to other antibacterials, prostatitis.

Question 4

Side effects

Answer 4

• Allergic reactions
• Blood dyscrasia
• Hyperkalaemia
• Anaphylaxis
• Photosensitivity
• Aspetic meningitis
• GI disturbances.

Question 5

Cautions and contraindications

Answer 5

Caution in RI
Pregnancy

Question 6

Blood dyscrasia

Answer 6

o Long term treatment: look out for signs of blood disorder
o Fever, sore throat, rash, mouth ulcers, bruising or bleeding development

Question 7

Pregnancy

Answer 7

• Trimethoprim is an antifolate
  o Teratogenic risk in 1st trimester – avoid in pregnancy
  o Interaction with other anti-folates e.g. methotrexate and phenytoin

Question 8

Trimethoprim + methotrexate

Answer 8

o Trimethoprim may increase the risk of side effects of methotrexate –
o Methotrexate and trimethoprim are both folate antagonists.
o A reduction in folic acid is thought to increase the side effects of methotrexate and thus concurrent use of trimethoprim and methotrexate can also increase the risk of nephrotoxicity

Question 9

What trimester should you avoid trimethoprim in?

Answer 9

1st

Question 10

Monitoring

Answer 10

Monitor blood counts on long-term therapy.

Question 11

What electrolyte imbalance does trimethoprim cause?

Answer 11

Hyperkalaemia