What antibiotics are most commonly prescribed empirically on an adult inpatient ward for common infections such as community‑acquired pneumonia, urinary tract infection, intra‑abdominal infection, skin‑soft‑tissue infection, and hospital‑acquired pneumonia?

Commonly Used Antibiotics in Inpatient Wards for Adult Infections

Community-Acquired Pneumonia (CAP)

Non-ICU Hospitalized Patients

The standard empiric regimen is ceftriaxone 1–2 g IV once daily plus azithromycin 500 mg IV or orally daily, providing comprehensive coverage of typical bacterial pathogens (Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis) and atypical organisms (Mycoplasma, Chlamydophila, Legionella). 1

• Alternative β-lactams include cefotaxime 1–2 g IV every 8 hours or ampicillin-sulbactam 3 g IV every 6 hours, always combined with azithromycin. 1
• Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily) is equally effective but should be reserved for penicillin-allergic patients due to FDA safety warnings about tendon rupture, peripheral neuropathy, and aortic dissection. 1
• Cefepime 2 g IV every 12 hours demonstrates comparable efficacy to ceftriaxone for pneumonia when combined with a macrolide, but is not first-line unless Pseudomonas risk factors exist. 2, 3

ICU Patients with Severe CAP

Combination therapy is mandatory for all ICU patients; β-lactam monotherapy is associated with higher mortality in critically ill individuals with bacteremic pneumococcal pneumonia. 1

• Preferred ICU regimen: ceftriaxone 2 g IV once daily plus azithromycin 500 mg IV daily (or a respiratory fluoroquinolone). 1
• For penicillin-allergic ICU patients, use aztreonam 2 g IV every 8 hours plus a respiratory fluoroquinolone. 1

Special Pathogen Coverage (Risk-Based Only)

Pseudomonas aeruginosa Coverage

Add antipseudomonal therapy only when specific risk factors are present: structural lung disease, recent hospitalization with IV antibiotics (≤90 days), or prior Pseudomonas isolation. 1

• Regimen: piperacillin-tazobactam 4.5 g IV every 6 hours plus ciprofloxacin 400 mg IV every 8 hours (or levofloxacin 750 mg IV daily) plus an aminoglycoside (gentamicin 5–7 mg/kg IV daily) for dual antipseudomonal coverage. 1

MRSA Coverage

Add MRSA therapy only when risk factors exist: prior MRSA infection/colonization, recent hospitalization with IV antibiotics, post-influenza pneumonia, or cavitary infiltrates on imaging. 1

• Regimen: vancomycin 15 mg/kg IV every 8–12 hours (target trough 15–20 µg/mL) or linezolid 600 mg IV every 12 hours, added to the base CAP regimen. 1

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Urinary Tract Infection (UTI)

Complicated UTI/Pyelonephritis

Ceftriaxone 1–2 g IV once daily provides reliable coverage of common uropathogens (E. coli, Klebsiella spp., Proteus spp.) and requires no renal dose adjustment. 1

• For ESBL-producing organisms, escalate to ertapenem 1 g IV daily or meropenem 1 g IV every 8 hours based on local resistance patterns. 1
• Piperacillin-tazobactam 4.5 g IV every 6 hours covers both typical uropathogens and provides broader gram-negative activity when polymicrobial infection is suspected. 4

Duration and Transition

• Treat complicated UTI for 7–14 days depending on severity and clinical response. 1
• Switch to oral therapy (ciprofloxacin 500 mg twice daily or levofloxacin 750 mg daily) when clinically stable and able to tolerate oral intake. 1

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Intra-Abdominal Infection

Empiric Coverage for Community-Acquired Infections

Ceftriaxone 1–2 g IV once daily plus metronidazole 500 mg IV every 8 hours provides adequate coverage of enteric gram-negative bacteria and anaerobes. 1

• Piperacillin-tazobactam 4.5 g IV every 6 hours offers single-agent coverage of gram-negatives, gram-positives, and anaerobes, making it a preferred option for moderate-to-severe infections. 4
• Ertapenem 1 g IV daily is an alternative for patients with β-lactam allergies or when ESBL organisms are suspected. 5

Healthcare-Associated or Severe Infections

• For suspected ESBL producers or higher-risk patients, use meropenem 1 g IV every 8 hours or imipenem 500 mg IV every 6 hours. 1
• Add vancomycin 15 mg/kg IV every 8–12 hours when MRSA or Enterococcus faecium is suspected. 1

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Skin and Soft-Tissue Infection (SSTI)

Non-Purulent Cellulitis

Ceftriaxone 1–2 g IV once daily or cefazolin 1–2 g IV every 8 hours targets Streptococcus pyogenes and methicillin-susceptible Staphylococcus aureus (MSSA). 1

• For penicillin-allergic patients, use clindamycin 600 mg IV every 8 hours or vancomycin 15 mg/kg IV every 8–12 hours. 1

Purulent SSTI (Abscess, Furuncle)

Vancomycin 15 mg/kg IV every 8–12 hours or linezolid 600 mg IV every 12 hours provides empiric MRSA coverage pending culture results. 1

• Ceftaroline 600 mg IV every 12 hours is an alternative with MRSA activity and may have superior cure rates in some studies. 5

Necrotizing Fasciitis or Severe SSTI

Piperacillin-tazobactam 4.5 g IV every 6 hours plus vancomycin 15 mg/kg IV every 8–12 hours plus clindamycin 600 mg IV every 8 hours ensures broad polymicrobial coverage including anaerobes, MRSA, and toxin suppression. 1

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

Standard Empiric Therapy (No MDR Risk)

Ceftriaxone 2 g IV once daily plus azithromycin 500 mg IV daily may be used for early-onset HAP (<5 days) without risk factors for resistant organisms. 1

MDR Risk Factors Present

When patients have recent IV antibiotics (≤90 days), prolonged hospitalization, or structural lung disease, use dual antipseudomonal coverage:

• Piperacillin-tazobactam 4.5 g IV every 6 hours (or cefepime 2 g IV every 8 hours) plus ciprofloxacin 400 mg IV every 8 hours (or levofloxacin 750 mg IV daily) plus an aminoglycoside (gentamicin 5–7 mg/kg IV daily). 1
• Add vancomycin 15 mg/kg IV every 8–12 hours or linezolid 600 mg IV every 12 hours when MRSA prevalence exceeds 10–20% or risk factors exist. 1

Novel Agents for Resistant Organisms

• Cefepime/enmetazobactam targets ESBL-producing Pseudomonas and Enterobacterales in HAP/VAP. 6
• Sulbactam/durlobactam is indicated for carbapenem-resistant Acinetobacter baumannii (CRAB) in HAP/VAP. 6

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Critical Timing and Monitoring Principles

Antibiotic Administration Timing

Administer the first antibiotic dose within 1 hour of diagnosis in critically ill patients; delays beyond 8 hours increase 30-day mortality by 20–30%. 1

Diagnostic Sampling

Obtain blood cultures and site-specific cultures (sputum, urine, wound) before the first antibiotic dose in all hospitalized patients to enable pathogen-directed therapy and safe de-escalation. 1

Duration of Therapy

• Minimum 5 days for CAP, continuing until afebrile for 48–72 hours with no more than one sign of clinical instability; typical total duration is 5–7 days for uncomplicated cases. 1
• Extend to 14–21 days only for specific pathogens (Legionella, S. aureus, gram-negative enteric bacilli) or complicated infections. 1

Transition to Oral Therapy

Switch from IV to oral antibiotics when the patient is hemodynamically stable (SBP ≥90 mmHg, HR ≤100 bpm), clinically improving, afebrile for 48–72 hours, respiratory rate ≤24 breaths/min, oxygen saturation ≥90% on room air, and able to take oral medication—typically by hospital day 2–3. 1

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Common Pitfalls to Avoid

• Never use macrolide monotherapy in hospitalized patients; it fails to cover typical pathogens such as S. pneumoniae and leads to treatment failure. 1
• Avoid indiscriminate use of antipseudomonal agents (piperacillin-tazobactam, cefepime) or MRSA coverage (vancomycin, linezolid) without documented risk factors; this promotes resistance without clinical benefit. 1
• Do not use ciprofloxacin or cefuroxime as first-line monotherapy for CAP; ciprofloxacin lacks adequate S. pneumoniae activity, and cefuroxime has less reliable coverage against drug-resistant strains. 7
• Do not delay antibiotic administration to await culture results; specimens should be collected rapidly, but therapy must start immediately. 1