# Antimicrobial Stewardship: De-escalation, Duration, and Resistance

## Introduction

Antimicrobial resistance is one of the greatest threats to global health. Antimicrobial stewardship programs (ASPs) aim to optimize antibiotic use by selecting the right drug, dose, and duration to improve patient outcomes while minimizing resistance, adverse effects, and cost. Every internist is a steward of antibiotics at the bedside.

## Principles of Antimicrobial Stewardship

### Core Strategies

- **Prospective audit and feedback**: infectious disease review of antibiotic orders with recommendations
- **Formulary restriction and preauthorization**: requiring approval for certain broad-spectrum agents
- **Antibiotic time-outs**: structured reassessment at 48-72 hours after culture data returns
- **De-escalation**: narrowing spectrum based on culture and susceptibility results
- **IV-to-oral conversion**: transitioning to equivalent oral agents when clinically appropriate

### The 5 D's of Antimicrobial Stewardship

- **Diagnosis**: Is there truly an infection requiring antibiotics?
- **Drug**: Is this the right antibiotic for the pathogen?
- **Dose**: Is the dose optimized for the site and severity?
- **Duration**: What is the shortest effective course?
- **De-escalation**: Can the spectrum be narrowed?

![Infographic illustrating the 5 D's of antimicrobial stewardship](/images/residency/stewardship-5ds.jpg)

## De-escalation in Practice

### When and How to De-escalate

- Review culture and sensitivity results at **48-72 hours** and narrow therapy
- Switch from empiric broad-spectrum agents to **targeted, narrow-spectrum antibiotics**
- Example: vancomycin + piperacillin-tazobactam started empirically; blood cultures grow MSSA; de-escalate to cefazolin
- De-escalation does **not** increase mortality and may reduce adverse effects and resistance

### Common De-escalation Opportunities

- **MSSA bacteremia**: vancomycin to cefazolin or nafcillin (superior outcomes with beta-lactams)
- **Susceptible Enterobacterales**: carbapenems to ceftriaxone or fluoroquinolones
- **Culture-negative sepsis improving clinically**: discontinue antibiotics if no source identified
- **Negative procalcitonin trend**: supports antibiotic discontinuation in lower respiratory infections

## Duration of Therapy: Evidence-Based Shorter Courses

### Conditions Where Shorter Courses Are Supported

| Infection | Evidence-Based Duration | Key Evidence |
|-----------|------------------------|--------------|
| Community-acquired pneumonia | 5 days (if stable x 48h) | Multiple RCTs |
| Uncomplicated cystitis | 3-5 days | IDSA guidelines |
| Pyelonephritis (fluoroquinolone) | 5-7 days | IDSA guidelines |
| Intra-abdominal infection (source controlled) | 4 days | STOP-IT trial |
| Uncomplicated cellulitis | 5-6 days | IDSA 2014 |
| HAP/VAP | 7 days | ATS/IDSA guidelines |
| Uncomplicated GNR bacteremia | 7 days | BALANCE trial |

- **Community-acquired pneumonia**: 5 days (if clinically stable for 48 hours); no benefit to 7-10 days
- **Uncomplicated urinary tract infection**: 3-5 days for cystitis; 5-7 days for pyelonephritis with fluoroquinolones
- **Intra-abdominal infection** with adequate source control: 4 days (STOP-IT trial)
- **Uncomplicated cellulitis**: 5-6 days if clinically improving
- **Hospital-acquired/ventilator-associated pneumonia**: 7 days (unless non-fermenting gram-negatives)
- **Uncomplicated gram-negative bacteremia**: 7 days (BALANCE trial)

### Tools to Guide Duration

- **Procalcitonin**: serial levels guide antibiotic discontinuation in pneumonia and sepsis
- **Clinical stability criteria**: afebrile, improving WBC, tolerating oral intake, hemodynamically stable
- Longer courses remain appropriate for endocarditis, osteomyelitis, and undrained abscesses

![Table summarizing evidence-based antibiotic duration recommendations by infection type](/images/residency/antibiotic-duration-table.jpg)

## Antimicrobial Resistance

### Key Resistance Patterns

| Resistant Organism | Treatment Options | Key Notes |
|-------------------|-------------------|-----------|
| MRSA | Vancomycin, daptomycin, linezolid | Beta-lactams (cefazolin) superior for MSSA |
| ESBL Enterobacterales | Carbapenems (first-line) | Avoid cephalosporins even if "susceptible" in vitro |
| CRE | Ceftazidime-avibactam, meropenem-vaborbactam, cefiderocol | ID consultation recommended |
| VRE | Linezolid, daptomycin | Common in GI tract colonization |
| Pseudomonas | Varies; always confirm susceptibilities | Intrinsic multi-drug resistance |
| C. difficile | Fidaxomicin, oral vancomycin | Consequence of FQ/clindamycin use |

- **MRSA**: methicillin-resistant *Staphylococcus aureus*; treat with vancomycin, daptomycin, or linezolid
- **ESBL-producing Enterobacterales**: extended-spectrum beta-lactamase producers; carbapenems are treatment of choice
- **CRE**: carbapenem-resistant Enterobacterales; ceftazidime-avibactam, meropenem-vaborbactam, or cefiderocol
- **VRE**: vancomycin-resistant *Enterococcus*; linezolid or daptomycin
- ***Pseudomonas aeruginosa***: intrinsic resistance to many agents; always confirm susceptibilities
- ***Clostridioides difficile***: consequence of broad-spectrum antibiotic use; fluoroquinolones and clindamycin are highest risk

### Risk Factors for Resistant Organisms

- Prior antibiotic exposure within 90 days
- Recent hospitalization or nursing facility residence
- Indwelling devices (catheters, lines)
- International travel (ESBL colonization)
- Prior culture data showing resistant organisms

## Common Stewardship Pitfalls

- Treating **asymptomatic bacteriuria** (except in pregnancy and pre-urologic procedures)
- Continuing broad-spectrum antibiotics despite negative cultures and clinical improvement
- Using antibiotics for **non-infectious diagnoses** (e.g., drug fever, gout flare, DVT misdiagnosed as cellulitis)
- Duplicate anaerobic coverage (e.g., metronidazole + piperacillin-tazobactam)
- Failure to adjust for renal or hepatic dysfunction

![Diagram showing the cycle of antibiotic overuse, resistance development, and C. difficile risk](/images/residency/resistance-cycle.jpg)

## IV-to-Oral Transition

- Most patients with functioning GI tracts can transition to oral antibiotics early
- **High oral bioavailability agents**: fluoroquinolones (~100%), linezolid (~100%), TMP-SMX (~95%), metronidazole (~100%), doxycycline (~95%)
- The OPAT (outpatient parenteral antibiotic therapy) model may be avoidable with appropriate oral agents
- **POET trial**: oral step-down noninferior to IV for left-sided endocarditis in stable patients

## Key Clinical Pearls

- Perform an antibiotic time-out at 48-72 hours on every patient receiving empiric antibiotics
- Shorter antibiotic courses are noninferior for most common infections; default to the evidence
- De-escalation to narrow-spectrum agents improves outcomes and reduces C. difficile risk
- Do not treat asymptomatic bacteriuria; positive urine cultures without symptoms are not infections
- Know which oral antibiotics have high bioavailability to facilitate early IV-to-oral switches

## References

1. Barlam TF, Cosgrove SE, Abbo LM, et al. Implementing an antibiotic stewardship program: guidelines by the IDSA and SHEA. *Clin Infect Dis*. 2016;62(10):e51-e77.
2. Sawyer RG, Claridge JA, Nathens AB, et al. Trial of short-course antimicrobial therapy for intraabdominal infection (STOP-IT). *N Engl J Med*. 2015;372(21):1996-2005.
3. Yahav D, Franceschini E, Koppel F, et al. Seven versus 14 days of antibiotic therapy for uncomplicated gram-negative bacteremia (BALANCE). *Clin Infect Dis*. 2019;69(7):1091-1098.
4. Iversen K, Ihlemann N, Gill SU, et al. Partial oral versus intravenous antibiotic treatment of endocarditis (POET). *N Engl J Med*. 2019;380(5):415-424.