PH8.1-2 | PH8.1-2 | Antimicrobial Principles and Stewardship — SDL Guide — Summary & Reflection

KEY TAKEAWAYS

Core principles of chemotherapy rest on selective toxicity — exploiting structural or metabolic differences between pathogen and host. Antimicrobials are classified as bacteriostatic (tetracyclines, macrolides, sulfonamides, chloramphenicol, clindamycin — need intact immunity) or bactericidal (β-lactams, aminoglycosides, fluoroquinolones, vancomycin, metronidazole, rifampicin — preferred for endocarditis, meningitis, immunocompromised states). Note: aminoglycosides are bactericidal despite being 30S ribosomal inhibitors.

PK/PD indices determine dosing strategy: AUC/MIC and Cmax/MIC (concentration-dependent — aminoglycosides, fluoroquinolones; once-daily dosing exploits PAE); T>MIC (time-dependent — β-lactams; frequent or continuous infusion).

Antimicrobial resistance arises by intrinsic mechanisms (structural exclusion) or acquired mechanisms: spontaneous mutation (rifampicin, fluoroquinolones) or horizontal gene transfer via plasmids/transposons. Molecular mechanisms: enzymatic inactivation (β-lactamases, aminoglycoside-modifying enzymes), efflux pumps, target site modification (PBP2a in MRSA, rRNA methylation for macrolides), and reduced permeability (porin loss).

Rational prescribing follows four steps: confirm antibiotic is needed → identify likely pathogen/site → assess host factors (allergy, renal function, pregnancy, immunosuppression, local antibiogram) → de-escalate on culture result.

Antimicrobial stewardship operationalises these principles at the institutional level: formulary restriction, prospective audit-and-feedback, IV-to-oral switch, PK/PD-guided dosing, and education. Key outcome metrics: CDI rates, MDRO incidence, DOT/1,000 patient-days, antibiotic expenditure.

REFLECT

Think about the last time you or a family member took antibiotics. Was a culture taken first? Was the duration evidence-based? Was there a specific clinical indication, or was it prescribed 'just in case'? Now imagine multiplying that prescribing decision by the millions of daily antibiotic orders written across India every day. How would you, as a future prescriber, change one specific behaviour in your own practice to improve rational antimicrobial use? What data would you need to know whether your hospital's antibiotic use is contributing to or reducing resistance?