What antibiotics are recommended for various bacterial infections, considering factors such as disease severity, patient's medical history, and potential antibiotic resistance?

Antibiotic Selection by Disease and Clinical Context

Community-Acquired Pneumonia (CAP)

For outpatients without comorbidities or recent antibiotic use, monotherapy with amoxicillin 500mg-1g PO q8h or a macrolide (azithromycin 500mg PO daily for 3-5 days) is recommended for 5-7 days. 1

Outpatient Treatment Algorithm

Low severity (CRB-65 0-1) without comorbidities:

• First-line: Amoxicillin 500mg-1g PO q8h, amoxicillin/clavulanate 1-2g PO q12h, or ampicillin/sulbactam 375-750mg PO q12h 1
• For presumed atypical pathogens: Azithromycin 500mg PO daily (3-5 days), clarithromycin 500mg PO q12h, or doxycycline 100mg PO q12h 1
• Duration: 5-7 days 1

With comorbidities or recent antibiotic use (past 3 months):

• Preferred: β-lactam (amoxicillin, amoxicillin/clavulanate, or cefuroxime) PLUS macrolide or doxycycline 1
• Alternative monotherapy: Respiratory fluoroquinolone (moxifloxacin 400mg PO daily, levofloxacin 500-750mg PO daily, or gemifloxacin 320mg PO daily) 1

Hospitalized Patients

Moderate severity (non-ICU):

• Preferred: Amoxicillin/clavulanate 1.2g IV q8h, ampicillin/sulbactam 1.5-3g IV q6h, ceftriaxone 2g IV daily, or cefotaxime 1-2g IV q8h PLUS azithromycin 500mg PO daily or clarithromycin 500mg IV/PO q12h 1
• Alternative: Respiratory fluoroquinolone monotherapy (moxifloxacin 400mg IV daily or levofloxacin 500-750mg IV daily) 1
• Duration: 5-7 days 1

Severe (ICU admission, CURB-65 ≥3):

• Mandatory β-lactam-based combination: Amoxicillin/clavulanate 1.2g IV q8h, ampicillin/sulbactam 1.5-3g IV q6h, ceftriaxone 2g IV daily, cefotaxime 1-2g IV q8h, or ertapenem 1g IV daily PLUS macrolide or respiratory fluoroquinolone 1
• Duration: 7 days 1

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Acute Bacterial Rhinosinusitis (ABRS)

For adults with mild disease and no recent antibiotic use, amoxicillin/clavulanate (1.75-4g/250mg daily) provides 90-91% clinical efficacy and 97-99% bacteriologic efficacy against S. pneumoniae and H. influenzae. 1

Adult Treatment Algorithm

Mild disease without recent antibiotic use (past 4-6 weeks):

• First-line: Amoxicillin/clavulanate 1.75-4g/250mg daily (higher doses for penicillin-resistant S. pneumoniae risk) 1
• Alternatives: Amoxicillin 1.5-4g/day, cefpodoxime proxetil, cefuroxime axetil, or cefdinir 1
• β-lactam allergic: TMP-SMX (83% efficacy), doxycycline (81% efficacy), or macrolides (77% efficacy—limited effectiveness, 20-25% bacterial failure possible) 1

Mild disease with recent antibiotic use OR moderate disease:

• Preferred: Respiratory fluoroquinolones (gatifloxacin/levofloxacin/moxifloxacin—92% clinical, 100% bacteriologic efficacy), amoxicillin/clavulanate 4g/250mg, or ceftriaxone 1
• Switch therapy if no improvement after 72 hours: Reevaluate patient with cultures, CT scan, or fiberoptic endoscopy 1

Pediatric Treatment Algorithm

Mild disease without recent antibiotic use:

• First-line: High-dose amoxicillin/clavulanate (90mg/6.4mg/kg/day—91-92% clinical efficacy) or high-dose amoxicillin (90mg/kg/day) 1
• Alternatives: Cefpodoxime proxetil, cefuroxime axetil, or cefdinir 1
• β-lactam allergic: TMP-SMX, azithromycin, clarithromycin, or erythromycin (limited effectiveness—20-25% bacterial failure) 1

With recent antibiotic use or moderate disease:

• Preferred: High-dose amoxicillin/clavulanate (90mg/6.4mg/kg/day) or ceftriaxone 1
• Switch therapy: Reevaluate patient if no improvement 1

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Skin and Soft Tissue Infections (SSTI)

Impetigo

Oral dicloxacillin 250mg q6h or cephalexin 250mg q6h for 5-10 days is first-line for limited impetigo; mupirocin ointment applied three times daily is appropriate for localized lesions. 1

• Alternatives: Clindamycin 300-400mg PO q8h, amoxicillin/clavulanate 875/125mg PO q12h, or erythromycin 250mg PO q6h (if susceptible) 1
• Pediatric: Dicloxacillin 12mg/kg/day in 4 divided doses or cephalexin 25mg/kg/day in 4 divided doses 1

Methicillin-Susceptible S. aureus (MSSA) SSTI

Outpatient:

• Preferred: Dicloxacillin 500mg PO q6h or cephalexin 500mg PO q6h 1
• Alternatives: Clindamycin 300-450mg PO q8h, doxycycline 100mg PO q12h, or TMP-SMX 1-2 double-strength tablets PO q12h 1

Inpatient:

• Preferred: Nafcillin or oxacillin 1-2g IV q4h (drug of choice) or cefazolin 1g IV q8h 1
• Penicillin-allergic: Clindamycin 600mg IV q8h 1

Methicillin-Resistant S. aureus (MRSA) SSTI

Outpatient:

• Preferred: Linezolid 600mg PO q12h, doxycycline 100mg PO q12h, or TMP-SMX 1-2 double-strength tablets PO q12h 1
• Alternative: Clindamycin 300-450mg PO q8h (if susceptible, check for inducible resistance) 1
• Duration: 5-10 days 1

Inpatient (complicated SSTI):

• Preferred: Vancomycin 30-60mg/kg/day IV in 2-4 divided doses (target trough 15-20 mcg/mL) 1
• Alternatives: Linezolid 600mg IV/PO q12h, daptomycin 4mg/kg IV daily, or teicoplanin 10mg/kg IV q12h for 3 doses then 6-10mg/kg daily 1
• Duration: 7-14 days 1

Cellulitis by Acquisition Setting

Community-acquired:

• Piperacillin-tazobactam or 3rd generation cephalosporin + oxacillin 1

Healthcare-associated:

• Area-dependent: Use nosocomial regimen if high MDRO prevalence or sepsis present 1

Nosocomial:

• 3rd generation cephalosporin or meropenem + oxacillin OR glycopeptides/daptomycin/linezolid 1

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Diabetic Foot Infections (DFI)

Empiric antibiotic selection must cover Gram-positive cocci (staphylococci and streptococci) in virtually all cases, with broader coverage for moderate-to-severe infections based on infection severity, recent antibiotic exposure, and local resistance patterns. 1

Mild Infections

Narrow-spectrum agents targeting aerobic Gram-positive cocci:

• Dicloxacillin, cephalexin, or clindamycin (if MRSA suspected and susceptible) 1
• Adjust based on culture results 1

Moderate-to-Severe Infections

Broader empiric coverage required:

• Add MRSA coverage if: High local MRSA prevalence, recent healthcare exposure, recent antibiotic therapy, or known MRSA colonization 1
• Add Gram-negative coverage if: Previous antibiotic therapy or more severe infection 1
• Add anti-pseudomonal therapy if: High local Pseudomonas prevalence, warm climate, or frequent foot water exposure 1
• Add anaerobic coverage if: Necrotic tissue, foul odor, or gas in tissues 1

Specific regimens:

• Piperacillin-tazobactam, ampicillin-sulbactam, or carbapenem (ertapenem if no Pseudomonas risk) PLUS vancomycin or linezolid if MRSA suspected 1

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Bacteremia and Endocarditis (MRSA)

Uncomplicated MRSA Bacteremia

Vancomycin 30-60mg/kg/day IV in 2-4 divided doses or teicoplanin 6-12mg/kg IV q12h for 3 doses then daily for 2 weeks. 1

Complicated MRSA Bacteremia

Vancomycin 30-60mg/kg/day IV in 2-4 divided doses or teicoplanin 6-12mg/kg IV q12h for 3-6 doses then 6-12mg/kg daily for 4-6 weeks. 1

• Alternative: Daptomycin 6-10mg/kg IV daily 1
• Do NOT add gentamicin or rifampin to vancomycin 1

Native Valve Endocarditis

Vancomycin 30-60mg/kg/day IV in 2-4 divided doses for 6 weeks. 1

Prosthetic Valve Endocarditis

Vancomycin 15mg/kg IV q6h PLUS rifampin 300mg PO q8h PLUS gentamicin 1mg/kg IV q8h for 6 weeks. 1

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Pneumonia (MRSA)

Vancomycin 30-60mg/kg/day IV in 2-4 divided doses or linezolid 600mg PO/IV q12h for 7-21 days. 1

• Alternatives: Teicoplanin 6-12mg/kg IV q12h for 3 doses then 6-12mg/kg daily 1
• Pediatric: Vancomycin 15mg/kg IV q6h or linezolid 10mg/kg PO/IV q8h (max 600mg/dose) 1

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Bone and Joint Infections (MRSA)

Osteomyelitis

Vancomycin 30-60mg/kg/day IV in 2-4 divided doses for >6 weeks. 1

• Alternatives: Daptomycin 6mg/kg IV daily, TMP-SMX (TMP 4mg/kg/dose PO/IV q8-12h) + rifampin 600mg PO daily, teicoplanin, or fusidic acid 500mg PO q8h + rifampin 1

Septic Arthritis

Vancomycin 30-60mg/kg/day IV in 2-4 divided doses for 3-4 weeks. 1

• Alternatives: Linezolid 600mg PO/IV q12h, daptomycin 6mg/kg IV daily, TMP-SMX + rifampin, teicoplanin, or fusidic acid + rifampin 1

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Central Nervous System Infections (MRSA)

Meningitis

Vancomycin 30-60mg/kg/day IV in 2-4 divided doses PLUS TMP-SMX (TMP 600mg PO daily or 300-450mg PO q12h) for 14 days. 1

• Alternative: Linezolid 600mg IV/PO q12h 1

Brain Abscess, Subdural Empyema, Spinal Epidural Abscess

Vancomycin 30-60mg/kg/day IV in 2-4 divided doses PLUS rifampin (5mg/kg IV q8-12h) for 4-6 weeks. 1

• Alternative: Linezolid 600mg IV/PO q12h 1

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Febrile Neutropenia

High-risk neutropenic patients require immediate hospitalization and IV monotherapy with an anti-pseudomonal β-lactam: cefepime, meropenem, imipenem-cilastatin, or piperacillin-tazobactam. 1

High-Risk Patients (Hospitalized)

Empiric monotherapy:

• Cefepime, meropenem, imipenem-cilastatin, or piperacillin-tazobactam 1

Add vancomycin ONLY for specific indications:

• Suspected catheter-related infection, skin/soft-tissue infection, pneumonia, or hemodynamic instability 1
• Do NOT use vancomycin routinely 1

Modify for resistant organisms if risk factors present:

• MRSA: Add vancomycin, linezolid, or daptomycin 1
• VRE: Add linezolid or daptomycin 1
• ESBL producers: Use carbapenem 1
• KPC producers: Consider polymyxin-colistin or tigecycline early 1

Low-Risk Patients (MASCC score ≥21)

Oral empiric therapy:

• Preferred: Ciprofloxacin PLUS amoxicillin-clavulanate 1
• Alternatives: Levofloxacin or ciprofloxacin monotherapy, or ciprofloxacin + clindamycin 1
• Do NOT use fluoroquinolone if patient on fluoroquinolone prophylaxis 1

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Infections in Cirrhosis and Liver Disease

Spontaneous Bacterial Peritonitis (SBP)

Community-acquired SBP:

• First-line: Cefotaxime 2g IV q8h for 5 days (covers 95% of ascitic fluid flora) 1, 2
• Alternative: Piperacillin-tazobactam 1, 2

Healthcare-associated or nosocomial SBP:

• If high MDRO prevalence: Carbapenem alone OR carbapenem + daptomycin/vancomycin/linezolid 1, 2
• Low resistance areas: Piperacillin-tazobactam 2

Critical caveat: Piperacillin-tazobactam can precipitate acute encephalopathy in cirrhosis due to decreased renal clearance; avoid amoxicillin-clavulanate due to high drug-induced liver injury rates 2

Pneumonia in Cirrhosis

Community-acquired:

• Piperacillin-tazobactam OR ceftriaxone + macrolide OR levofloxacin/moxifloxacin 1, 2

Nosocomial:

• Ceftazidime OR meropenem + levofloxacin ± glycopeptides or linezolid 1, 2

Alternative for critically ill with liver disease:

• Piperacillin-tazobactam (safe in liver disease) + azithromycin 500mg IV daily OR doxycycline 100mg IV/PO q12h 2
• Add aminoglycoside (gentamicin/amikacin) if septic shock for dual pseudomonal coverage 2

Urinary Tract Infections in Cirrhosis

Uncomplicated community-acquired:

• Ciprofloxacin or cotrimoxazole 1

With sepsis:

• 3rd generation cephalosporin or piperacillin-tazobactam 1

Nosocomial with sepsis:

• Meropenem + teicoplanin or vancomycin 1

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Key Antibiotic Safety Considerations in Liver Disease

Safest antibiotics: Third-generation cephalosporins, piperacillin-tazobactam, and fluoroquinolones (with caution) 2

Avoid or reduce doses: Rifampicin, isoniazid, macrolides (erythromycin/clarithromycin cause cholestasis), clofazimine, rifabutin, TMP-SMX 2

Monitor LFTs every 2-3 days if using levofloxacin (rare acute hepatitis risk); avoid moxifloxacin if transaminases >5x upper limit normal 2

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Critical Pitfalls to Avoid

• Never delay antibiotics in suspected severe infection: Empiric therapy must be started immediately after cultures obtained 1, 3
• Recent antibiotic use (past 3-6 months) mandates broader coverage: Assume resistant organisms 1
• Macrolides have 20-25% bacterial failure rates for ABRS: Use only if β-lactam allergic 1
• Do NOT routinely add vancomycin to neutropenic fever regimens: Reserve for specific indications only 1
• Penicillin-allergic patients usually tolerate cephalosporins: Avoid only if immediate hypersensitivity (hives, bronchospasm) 1
• Switch from IV to oral therapy cautiously in complicated bacteremia: Not recommended 1
• Fluoroquinolone prophylaxis precludes fluoroquinolone empiric therapy 1