Antimicrobial Agents, Pharmacology, and Stewardship
Core concepts
Antimicrobial pharmacology ties dose to killing pattern. Beta-lactams are time-dependent: keep free drug above the MIC. Aminoglycosides are concentration-dependent: extended-interval dosing maximizes peak/MIC and limits toxicity. Vancomycin and fluoroquinolones are AUC/MIC-dependent. Neonates have immature renal clearance, so intervals are longer. Stewardship means the right drug, dose, route, and shortest effective duration; avoid antibiotics for viral upper respiratory infection and for acute otitis media when criteria for observation are met.
Traps
- Ceftriaxone is avoided in neonates (bilirubin displacement, calcium precipitation).
- Fluoroquinolones have pediatric indications (for example, complicated urinary infection, certain resistant organisms); do not withhold when indicated, but counsel on adverse effects.
- Doxycycline is generally avoided under 8 years, but is used for rickettsial disease when benefits outweigh risks.
- Penicillin allergy labels are often inaccurate; cross-reactivity with cephalosporins is low.
- Vancomycin monitoring now uses AUC, not trough alone.
Worked example
A 5-year-old with nonpurulent cellulitis and no MRSA risk factors: cephalexin is appropriate. If there is purulence or MRSA risk, use clindamycin or trimethoprim-sulfamethoxazole. Reserve vancomycin for severe or systemic MRSA disease.
Rule of thumb: start broad only when the patient is unstable; narrow once culture and clinical data allow, and always state a stop date.