Trimethoprim-Sulfamethoxazole
Bactrim · Septra · TMP-SMX
Folate-synthesis inhibitor combination antibiotic
Sequential blockade of folate synthesis (TMP inhibits dihydrofolate reductase; SMX inhibits dihydropteroate synthase).
Indications
- •MRSA (SSTI), UTI, PCP (Pneumocystis) treatment + prophylaxis, Stenotrophomonas
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| PCP treatment | 15–20 mg/kg/day (TMP component) IV divided q6–8h | — |
| UTI/SSTI | 1–2 DS tabs PO q12h | — |
Pharmacokinetics
Half-life ~10 h. Renally cleared.
Side effects
- !HYPERKALEMIA (TMP blocks distal Na/K exchange — amiloride-like)
- !Sulfa allergy / SJS-TEN
- !Bone-marrow suppression
- !AKI/↑ creatinine (blocks tubular secretion)
- !↑ warfarin, ↑ sulfonylurea hypoglycemia
Contraindications
- ×Sulfa allergy
- ×Pregnancy (near term)/neonates (kernicterus)
- ×Severe renal failure
- ×G6PD deficiency (hemolysis)
Clinical pearls
- ★HYPERKALEMIA is the anesthesia-relevant surprise (TMP is amiloride-like) — check K⁺, esp. with ACEi/ARB/renal disease.
- ★Potentiates warfarin + sulfonylureas; sulfa allergy → SJS/TEN risk.
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
