Unit
- Definition and scope: Antimicrobial therapy encompasses the use of drugs to treat infections caused by bacteria, viruses, fungi, and parasites. Its primary goal is to eradicate or suppress the pathogenic microorganism while minimizing harm to the host. Effective management requires understanding the drug's spectrum, mechanism, and patient factors.
- Historical context: The discovery of penicillin in 1928 revolutionized medicine, transforming once-fatal infections into treatable conditions. The subsequent development of numerous classes dramatically reduced mortality from infectious diseases. However, widespread use has accelerated resistance.
- Selective toxicity: The ideal antimicrobial exploits differences between microbial and human cells, targeting structures or processes unique to the pathogen. Examples include cell wall synthesis (absent in human cells) and bacterial ribosomes. This principle underlies safe and effective therapy.
- Therapeutic index: The ratio between toxic and therapeutic doses determines safety. Drugs with a narrow therapeutic index, such as aminoglycosides, require careful monitoring. A wide index (e.g., penicillins) permits higher doses with less risk.
- Bactericidal vs. bacteriostatic: Bactericidal agents kill pathogens directly, while bacteriostatic agents inhibit growth, relying on host immunity for clearance. In immunocompromised patients, bactericidal drugs are often preferred. This classification influences clinical decisions, especially in severe infections.
- Spectrum of activity: Broad-spectrum agents cover a wide range of organisms but disrupt normal flora, predisposing to superinfections like Clostridioides difficile. Narrow-spectrum agents target specific pathogens, preserving microbiota and reducing resistance selection.
- Empiric vs. targeted therapy: Empiric therapy begins before pathogen identification, based on likely organisms and local resistance patterns. Once cultures and susceptibilities return, therapy is narrowed or adjusted. This approach balances timely treatment with stewardship.
- Multidisciplinary approach: Effective antimicrobial management involves collaboration among prescribers, pharmacists, microbiologists, and infection prevention teams. Each contributes unique expertise, from dosing optimization to resistance surveillance.
- Resistance mechanisms: Pathogens develop resistance through mutation, horizontal gene transfer, and selective pressure. Common mechanisms include enzymatic degradation, target modification, efflux pumps, and altered membrane permeability. Understanding local resistance patterns is critical for guiding empiric therapy and designing effective stewardship interventions to preserve antimicrobial effectiveness.
- Pharmacokinetics and pharmacodynamics (PK/PD): PK describes drug absorption, distribution, metabolism, and excretion; PD describes the drug's effect on microorganisms. Time dependent killing, as with beta-lactams, requires sustained concentrations above the MIC, while concentration dependent killing, as with fluoroquinolones, relies on high peak levels. Integrating PK/PD principles optimizes dosing regimens for maximal efficacy and minimal toxicity.
- De-escalation and duration: Once culture results identify the pathogen and its susceptibility, therapy should be narrowed from broad spectrum to targeted coverage. Shortening the treatment course to the minimum effective duration reduces resistance selection, adverse effects, and healthcare costs. Evidence supports shorter durations for many infections, such as five days for uncomplicated urinary tract infections.
Scope of Practice
Role: Clinical Pharmacist in Antimicrobial Stewardship
Within scope:
- Reviewing antimicrobial orders for appropriateness, dose, and duration
- Providing dosing recommendations based on renal function and drug levels
- Educating healthcare staff on antimicrobial guidelines and resistance trends
Outside scope:
- Diagnosing infections or selecting therapy without prescriber input
- Prescribing antimicrobials independently (unless authorized by collaborative practice agreement)
- Interpreting culture results beyond susceptibility data
Quick Revision
- Antimicrobial therapy aims to eradicate pathogens while minimizing host harm through selective toxicity.
- Understanding bactericidal vs. bacteriostatic and spectrum of activity guides appropriate selection.
- Empiric therapy is initiated based on likely pathogens; targeted therapy follows susceptibility results.
- Multidisciplinary collaboration optimizes patient outcomes and combats resistance.