What are common empirical antibiotics for various infections?

Empirical Antibiotic Selection by Infection Type

Skin and Soft Tissue Infections

For mild skin and soft tissue infections, use amoxicillin-clavulanate, cloxacillin, or cefalexin as first-line agents. 1

Mild Infections

• Amoxicillin-clavulanate (Access group antibiotic) 1
• Cloxacillin or other anti-staphylococcal penicillins (Access group) 1
• Cefalexin (Access group) 1
• Alternative: Dicloxacillin, clindamycin, or doxycycline 1

MRSA Coverage (when suspected)

• Vancomycin 15 mg/kg IV every 12 hours 1
• Linezolid 600 mg PO/IV every 12 hours (superior clinical cure vs vancomycin, OR 1.41) 2
• Daptomycin 6-8 mg/kg IV daily 2
• Oral options: Sulfamethoxazole-trimethoprim, doxycycline, or clindamycin 1, 2

Necrotizing Fasciitis

Initiate vancomycin or linezolid PLUS piperacillin-tazobactam immediately, or use ceftriaxone plus metronidazole. 1

• Combination: Clindamycin (Access) + piperacillin-tazobactam (Watch) with or without vancomycin 1
• Alternative: Ceftriaxone (Watch) + metronidazole (Access) with or without vancomycin 1
• For confirmed Group A Streptococcus: Penicillin + clindamycin 1

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Respiratory Tract Infections

Community-Acquired Pneumonia (CAP)

For outpatients without comorbidities, use a macrolide or doxycycline; with comorbidities, use a respiratory fluoroquinolone or beta-lactam plus macrolide. 1

Outpatient - No Comorbidities

• Macrolide (clarithromycin preferred over erythromycin due to fewer adverse events) 1
• Doxycycline 1

Outpatient - With Comorbidities

• Respiratory fluoroquinolone (levofloxacin, moxifloxacin) 1
• Beta-lactam + macrolide (ceftriaxone, cefotaxime, or ampicillin-sulbactam plus macrolide) 1

ICU/Severe CAP

• Ceftriaxone or cefotaxime + macrolide 1, 2
• Respiratory fluoroquinolone (levofloxacin or moxifloxacin) 1

Suspected Pseudomonas aeruginosa

• Piperacillin-tazobactam or carbapenem + ciprofloxacin/levofloxacin 1
• Alternative: Beta-lactam + aminoglycoside + azithromycin 1

Suspected MRSA

• Add vancomycin or linezolid to above regimens 1

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Intra-Abdominal Infections

For mild to moderate intra-abdominal infections, use amoxicillin-clavulanate; for severe infections, use ceftriaxone plus metronidazole or piperacillin-tazobactam. 2

Mild to Moderate

• Amoxicillin-clavulanate 2
• Ampicillin + gentamicin + metronidazole (in children) 2

Severe/Complicated

• Cefotaxime or ceftriaxone + metronidazole 2
• Piperacillin-tazobactam 1, 2
• Ertapenem 1
• Ciprofloxacin + metronidazole (better clinical cure than beta-lactams, OR 1.69) 1

Hospital-Acquired/Critically Ill

• Piperacillin-tazobactam 2
• Carbapenems (meropenem, imipenem, doripenem) 2
• Tigecycline (associated with more adverse events and higher mortality, OR 1.33) 1

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Surgical Site Infections

Intestinal/Genitourinary Tract Surgery

Use piperacillin-tazobactam or a carbapenem as single-drug regimens, or ceftriaxone plus metronidazole for combination therapy. 1

Single-Drug Regimens

• Piperacillin-tazobactam 3.375 g every 6 hours or 4.5 g every 8 hours IV 1
• Carbapenems: Imipenem 500 mg every 6 hours, meropenem 1 g every 8 hours, or ertapenem 1 g every 24 hours IV 1

Combination Regimens

• Ceftriaxone 1 g every 24 hours + metronidazole 500 mg every 8 hours IV 1
• Ciprofloxacin 400 mg IV every 12 hours + metronidazole 500 mg every 8 hours 1
• Ampicillin-sulbactam 3 g every 6 hours + gentamicin 5 mg/kg every 24 hours 1

Trunk/Extremity Surgery (Away from Axilla/Perineum)

• Cefazolin 0.5-1 g every 8 hours IV 1
• Oxacillin or nafcillin 2 g every 6 hours IV 1
• Cefalexin 500 mg every 6 hours PO 1
• Vancomycin 15 mg/kg every 12 hours IV (for MRSA) 1

Axilla/Perineum Surgery

• Ceftriaxone 1 g every 24 hours + metronidazole 500 mg every 8 hours 1
• Fluoroquinolone (ciprofloxacin or levofloxacin) + metronidazole 1

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Diabetic Wound Infections

For mild diabetic wound infections, use dicloxacillin, cefalexin, or amoxicillin-clavulanate; for moderate to severe infections, use levofloxacin, ceftriaxone, or ertapenem. 1

Mild Infections

• Dicloxacillin, cefalexin, or amoxicillin-clavulanate 1
• Clindamycin, levofloxacin, or doxycycline 1
• For MRSA: Sulfamethoxazole-trimethoprim 1

Moderate to Severe Infections

• Levofloxacin, ceftriaxone, or ampicillin-sulbactam 1
• Ertapenem, moxifloxacin, or tigecycline 1
• Ciprofloxacin + clindamycin 1
• For MRSA: Linezolid, daptomycin, or vancomycin 1

Pseudomonas Coverage

• Piperacillin-tazobactam, ceftazidime, cefepime, or carbapenems 1

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Vertebral Osteomyelitis

For empiric therapy of native vertebral osteomyelitis, use vancomycin plus a third- or fourth-generation cephalosporin to cover staphylococci (including MRSA) and gram-negative bacilli. 1

Empiric Regimens

• Vancomycin + cefepime 1
• Vancomycin + ciprofloxacin 1
• Vancomycin + carbapenem 1
• Alternative (if allergic): Daptomycin + quinolone 1

Oxacillin-Susceptible Staphylococci

• Nafcillin or oxacillin 1.5-2 g IV every 4-6 hours 1
• Cefazolin 1-2 g IV every 8 hours 1
• Ceftriaxone 2 g IV every 24 hours 1

Oxacillin-Resistant Staphylococci (MRSA)

• Vancomycin 15-20 mg/kg IV every 12 hours (monitor levels) 1
• Daptomycin 6-8 mg/kg IV every 24 hours 1
• Linezolid 600 mg PO/IV every 12 hours 1

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Sepsis and Septic Shock

For sepsis, initiate broad-spectrum antimicrobials within one hour, covering gram-positive, gram-negative, and anaerobic organisms based on suspected source. 3

General Principles

• Administer antibiotics within 1 hour of recognition (risk of progression to shock increases 8% per hour of delay) 3
• Cover typical gram-positive and gram-negative organisms 3
• Add anaerobic coverage for intra-abdominal or other anaerobic sources 3

Empiric Regimens for Healthcare-Associated Sepsis

• Vancomycin + piperacillin-tazobactam 4, 3
• Vancomycin + cefepime 4, 3
• Vancomycin + carbapenem 4, 3
• Consider antifungal therapy in high-risk patients 3

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Bite Wounds

Animal Bites

Use amoxicillin-clavulanate orally or ampicillin-sulbactam intravenously for animal bites. 1

• Oral: Amoxicillin-clavulanate 1
• IV: Ampicillin-sulbactam, piperacillin-tazobactam, or second/third-generation cephalosporins 1
• Alternatives: Doxycycline, sulfamethoxazole-trimethoprim, or fluoroquinolones 1
• Anaerobic coverage: Metronidazole or clindamycin 1

Human Bites

• Amoxicillin-clavulanate or ampicillin-sulbactam 1
• Alternatives: Carbapenems or doxycycline 1
• For multidrug-resistant organisms: Vancomycin, daptomycin, linezolid, or colistin 1

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Key Stewardship Principles

AWaRe Classification

• Access antibiotics (amoxicillin-clavulanate, cloxacillin, cefalexin, clindamycin, metronidazole): First-line for most common infections with lower resistance potential 1
• Watch antibiotics (fluoroquinolones, third-generation cephalosporins, piperacillin-tazobactam, carbapenems, vancomycin): Use for specific indications or when Access antibiotics inadequate; require stewardship monitoring 1
• Reserve antibiotics: Last-resort options for multidrug-resistant organisms only 1

Duration and De-escalation

• Most community-acquired infections require 5-7 days of therapy; severe infections may need 10-14 days 2
• Expect clinical improvement within 3 days 2
• De-escalate therapy based on culture results and clinical response 2-4 days after initiation 4
• Inadequate initial empiric therapy increases mortality and cannot be remedied by later modification 4, 3

Common Pitfalls to Avoid

• Avoid fluoroquinolones as first-line due to resistance concerns and adverse effects (tendon, muscle, joint, nerve, CNS) 1, 2
• Do not use clindamycin for B. fragilis without checking local susceptibility 2
• Ensure adequate MRSA coverage when suspected (vancomycin, linezolid, or daptomycin) 2
• Avoid broad-spectrum agents for mild infections treatable with narrow-spectrum options 2
• Do not delay antibiotics in sepsis to obtain cultures; administer within 1 hour 3