Antimicrobials/Other antibacterials

Metronidazole, nitrofurantoin, trimethoprim & others

also: metronidazole · nitrofurantoin · trimethoprim · co-trimoxazole · clindamycin

Overview

The high-yield "miscellaneous" antibacterials — each with a signature niche and warning.

Mechanism

Metronidazole → DNA damage in anaerobes/protozoa. Nitrofurantoin concentrates in urine (multiple intracellular targets). Trimethoprim ± sulfamethoxazole inhibit folate synthesis. Clindamycin (lincosamide) inhibits the 50S ribosome + suppresses toxin production.

The agents

Metronidazolenitroimidazole

PO/IV/PR

Anaerobes, C. diff, BV, dental; disulfiram reaction with alcohol.

Nitrofurantoinnitrofuran

oral

Lower UTI 1st-line; avoid eGFR <45 + at term (neonatal haemolysis); pulmonary fibrosis (long-term).

Trimethoprim / co-trimoxazolefolate inhibitor

UTI; co-trimoxazole = PJP. Avoid trimethoprim 1st-trimester (NTD); hyperkalaemia; + methotrexate toxicity.

Clindamycinlincosamide

Necrotising fasciitis (toxin suppression), cellulitis in pen allergy; HIGHEST C. diff risk.

Adverse effects

Clindamycin: C. difficile (highest risk)serious

Metronidazole: disulfiram reaction, metallic taste, neuropathycommon

Co-trimoxazole: SJS, marrow suppression, hyperkalaemia, AKIserious

Nitrofurantoin: pulmonary fibrosis, neuropathy, brown urinecommon

Cautions & contraindications

Trimethoprim/co-trimoxazole in 1st-trimester pregnancypregnancy

Folate antagonist → NTD.

Nitrofurantoin at term / eGFR <45renal

Neonatal haemolysis / ineffective.

Metronidazole + alcoholall

Disulfiram reaction.

Interactions

Metronidazole/co-trimoxazole + warfarin; trimethoprim/co-trimoxazole + methotrexate/K⁺-raising drugs

Monitoring & kinetics

Co-trimoxazole: FBC, U&E, K⁺; nitrofurantoin long-term: respiratory

Mostly oral. Each has a defining niche + warning.

Choosing it

Spectrum: Metronidazole: anaerobes + protozoa. Nitrofurantoin/trimethoprim: lower-UTI uropathogens. Co-trimoxazole: PJP. Clindamycin: Gram+/anaerobes + toxin suppression.

Source: BNF — Antibacterials