What are the common inpatient antibiotic regimens for treating various infections?

Inpatient Antibiotics: A Comprehensive Guide

Inpatient antibiotic therapy should be guided by the site of infection, severity of illness, and local resistance patterns, with empiric regimens covering the most likely pathogens followed by targeted therapy based on culture results. 1

Common Intra-Abdominal Infections

Complicated Intra-Abdominal Infections (cIAI)

Single-Agent Regimens

• Piperacillin-tazobactam: 3.375g IV every 6h or 4.5g every 8h 1, 2
• Ertapenem: 1g IV every 24h 1
• Imipenem/cilastatin: 500mg IV every 6h or 1g every 8h 1
• Meropenem: 1g IV every 8h 1

Combination Regimens

• Ceftriaxone 1g IV every 24h + metronidazole 500mg IV every 8h 1
• Ciprofloxacin 400mg IV every 12h + metronidazole 500mg IV every 8h 1
• Cefepime 2g IV every 8-12h + metronidazole 500mg IV every 8h 1

Memory Aid: "PEMCiM"

• Piperacillin-tazobactam (broad coverage)
• Ertapenem (once daily, no Pseudomonas coverage)
• Meropenem/imipenem (for severe infections)
• Ciprofloxacin + Metronidazole (for penicillin-allergic patients)

Duration of Therapy

• 4-7 days after adequate source control 1
• Short course (3-5 days) is sufficient for most patients with adequate source control 1

Skin and Soft Tissue Infections (SSTIs)

Methicillin-Susceptible S. aureus (MSSA)

• Nafcillin or oxacillin: 1-2g IV every 4h 1
• Cefazolin: 1g IV every 8h 1
• Clindamycin: 600mg IV every 8h (if susceptible) 1

Methicillin-Resistant S. aureus (MRSA)

• Vancomycin: 15-20mg/kg IV every 8-12h 1
• Linezolid: 600mg IV/PO every 12h 1
• Daptomycin: 4mg/kg IV daily (for non-pneumonia infections) 1, 3
• Clindamycin: 600mg IV every 8h (if susceptible) 1

Memory Aid: "VLDCT"

• Vancomycin (first-line)
• Linezolid (good tissue penetration)
• Daptomycin (rapid bactericidal activity)
• Clindamycin (if susceptible)
• TMP-SMX (for less severe infections)

Complicated SSTIs Requiring Broad Coverage

• Vancomycin 15-20mg/kg IV every 8-12h + piperacillin-tazobactam 3.375g IV every 6h 1
• Vancomycin 15-20mg/kg IV every 8-12h + cefepime 2g IV every 8h + metronidazole 500mg IV every 8h 1, 4

Pneumonia

Community-Acquired Pneumonia (CAP)

• Ceftriaxone 1g IV daily + azithromycin 500mg IV/PO daily 1
• Levofloxacin 750mg IV/PO daily (monotherapy) 1

Hospital-Acquired/Ventilator-Associated Pneumonia (HAP/VAP)

• Piperacillin-tazobactam 4.5g IV every 6h 2, 1
• Cefepime 2g IV every 8h + vancomycin 15-20mg/kg IV every 8-12h 4, 1
• Meropenem 1g IV every 8h + vancomycin 15-20mg/kg IV every 8-12h (for suspected resistant organisms) 1

Memory Aid: "PACE VAP"

• Piperacillin-tazobactam
• Antipseudomonal cephalosporin (Cefepime)
• Carbapenem (Meropenem)
• Each paired with Vancomycin for Adequate Pneumonia coverage

Urinary Tract Infections (UTIs)

Uncomplicated Pyelonephritis

• Ceftriaxone 1g IV daily 1
• Ciprofloxacin 400mg IV every 12h 1

Complicated UTIs/Urosepsis

• Piperacillin-tazobactam 3.375g IV every 6h 2, 1
• Cefepime 2g IV every 12h 1, 4
• Meropenem 1g IV every 8h (for suspected ESBL-producers) 1

Bone and Joint Infections

Osteomyelitis/Septic Arthritis

• MSSA: Nafcillin/oxacillin 2g IV every 4h or cefazolin 2g IV every 8h 1
• MRSA: Vancomycin 15-20mg/kg IV every 8-12h 1
• Gram-negative: Ceftazidime 2g IV every 8h or cefepime 2g IV every 8h 1, 4

Special Populations

Pediatric Patients

• For febrile infants 8-21 days: Ampicillin 150mg/kg/day IV divided every 8h + ceftazidime 150mg/kg/day IV divided every 8h or gentamicin 4mg/kg IV every 24h 1
• For febrile infants 22-60 days: Ceftriaxone 50mg/kg IV every 24h 1
• For pediatric appendicitis/peritonitis (>9 months): 112.5mg/kg piperacillin-tazobactam IV every 8h 2, 1

Practical Considerations for Antibiotic Use

Dosing Adjustments

• Renal impairment: Adjust doses based on creatinine clearance, particularly for beta-lactams and vancomycin 2, 3
• Obese patients: Consider adjusted body weight for aminoglycosides; total body weight for vancomycin 1

Duration of Therapy

• Uncomplicated infections with adequate source control: 3-5 days 1
• Complicated infections: 7-14 days, based on clinical response 1
• Bone/joint infections: 4-6 weeks typically required 1

Memory Aids for Common Antibiotic Classes

Beta-lactams

• Penicillins: Time-dependent killing, good for streptococci
• Cephalosporins: Generations 1-5 with increasing gram-negative coverage
• Carbapenems: Broadest spectrum, reserve for resistant organisms

Non-beta-lactams

• Vancomycin: MRSA, requires therapeutic drug monitoring
• Fluoroquinolones: Concentration-dependent killing, good bioavailability
• Aminoglycosides: Concentration-dependent with post-antibiotic effect, nephrotoxic

Common Pitfalls and Caveats

• Failure to de-escalate: Always narrow therapy based on culture results to prevent resistance 1
• Inadequate dosing: Ensure optimal PK/PD parameters, especially in critically ill patients 1, 2
• Prolonged therapy: Longer isn't better; appropriate duration based on infection site and source control 1
• Ignoring local resistance patterns: Hospital antibiograms should guide empiric therapy 1
• Missing source control: Antibiotics alone are insufficient without adequate drainage/debridement 1

By organizing antibiotics by infection site and using memory aids, you can more easily recall appropriate regimens for common inpatient infections, improving patient outcomes while practicing good antibiotic stewardship.