Metronidazole
Flagyl
Nitroimidazole antibiotic (anaerobic + antiprotozoal)
Reduced intracellularly to reactive radicals → DNA damage in anaerobes/protozoa.
Indications
- •Anaerobic coverage (intra-abdominal, colorectal prophylaxis with a cephalosporin)
- •C. difficile (mild)
- •Bacterial vaginosis, trichomonas, amebiasis, H. pylori
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Anaerobic/prophylaxis | 500 mg IV q8h (or 15 mg/kg load) | — |
Pharmacokinetics
Half-life ~8 h. Hepatic. Good tissue/CNS penetration.
Side effects
- !DISULFIRAM-LIKE reaction with alcohol (avoid alcohol during + 3 days after)
- !Metallic taste
- !Peripheral neuropathy (prolonged)
- !↑ warfarin effect (INR)
Contraindications
- ×Alcohol use / alcohol-containing preparations
- ×1st trimester (relative)
Clinical pearls
- ★Disulfiram-like reaction with alcohol — the classic teaching point.
- ★Potentiates warfarin (raises INR); pairs with a cephalosporin for anaerobic colorectal prophylaxis.
Other drugs in Antibiotics
- Cefazolin
β-lactam — inhibits bacterial cell wall PBPs.
- Vancomycin
Inhibits cell wall synthesis (binds D-Ala-D-Ala). Active against MRSA + gram-positives.
- Clindamycin
Binds 50S ribosomal subunit, blocks peptide-bond formation. Bacteriostatic against most organisms; bactericidal against susceptible streptococci. Excellent activity against anaerobes and gram-positive cocci including community-acquired MRSA.
- Gentamicin
Binds 30S ribosomal subunit, causes misreading of mRNA → defective bacterial protein synthesis. Bactericidal, concentration-dependent killing. Synergy with cell-wall agents (β-lactams, vancomycin) for gram-positive endocarditis.
- Cefuroxime
β-lactam — inhibits cell-wall synthesis (PBP binding). 2nd-gen: gram-positive + expanded gram-negative.
- Cefepime
β-lactam cell-wall inhibitor. Broad gram-negative (incl. Pseudomonas) + gram-positive coverage.
- Cefotetan
β-lactam; adds anaerobic (B. fragilis) coverage → colorectal/gynecologic prophylaxis.
- Cefotaxime
β-lactam cell-wall inhibitor. Broad gram-negative + CNS penetration.
Browse all classes: /reference/drugs
Suggested reading
- •Miller's Anesthesia, 9e
- •FDA package insert
