CLASSES OF ABX: TRIMETHOPRIM Flashcards
MOA
- Trimethoprim binds to and reversibly inhibits bacterial dihydrofolate reductase (DHFR) and blocks the production of tetrahydrofolate.
Activity against
Gram +
Aerobic Gram -
including enterobacteria Escherichia coli, Klebsiella pneumoniae, Streptococcus pneumoniae, Haemophilus influenzae and Staphylococcus aureus.
indications
- Pneumonia
- Respiratory tract infections
- Shigellosis
- Invasive salmonella
- Urinary-tract infections
- Acne resistant to other antibacterials, prostatitis.
Side effects
- Allergic reactions
- Blood dyscrasia
- Hyperkalaemia/ hyponatraemia
- Anaphylaxis
- Photosensitivity
- Aspetic meningitis
- GI disturbances.
Cautions and contraindications
Caution in RI
Pregnancy
Blood dyscrasia
o Long term treatment: look out for signs of blood disorder
o Fever, sore throat, rash, mouth ulcers, bruising or bleeding development
Pregnancy
- Trimethoprim is an antifolate
o Teratogenic risk in 1st trimester – avoid in pregnancy
o Interaction with other anti-folates e.g. methotrexate and phenytoin
Interactions
- Nephrotoxicity
- NSAIDs, tacrolimus, ciclosporin - Hyper K: ACEi, ARBs, spironolactone
- HypoNa: NSAIDs, SSRIs, TCAs, carbamazepine
- MOA
- Methotrexate - bone marrow suppression
Trimethoprim + methotrexate
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
What trimester should you avoid trimethoprim in?
1st
Monitoring
Monitor blood counts on long-term therapy.
What electrolyte imbalance does trimethoprim cause?
Hyperkalaemia
Hyponatraemia
