Imipenem-Cilastatin
Primaxin
Carbapenem β-lactam (broadest-spectrum)
β-lactam cell-wall inhibitor with very broad gram-positive/negative/anaerobic coverage. Cilastatin blocks renal dehydropeptidase (prevents imipenem degradation + nephrotoxic metabolite).
Indications
- •Severe polymicrobial/resistant infections
- •Febrile neutropenia
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Serious infection | 500 mg IV q6h (renally adjusted) | — |
Pharmacokinetics
Half-life ~1 h. Renally cleared.
Side effects
- !SEIZURES (highest seizure risk of the carbapenems, esp. renal failure/CNS disease/high dose)
- !C. difficile
- !Cross-reactivity with penicillin allergy (low but real)
Contraindications
- ×Seizure disorder (relative)
- ×Severe β-lactam allergy
- ×Renal failure without adjustment
Clinical pearls
- ★Highest seizure potential of the carbapenems — dose-adjust in renal failure, caution with CNS disease.
- ★Lowers valproate levels significantly (loss of seizure control) — avoid the combination.
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.
Suggested reading
- •Miller's Anesthesia, 9e
- •FDA package insert
