What are the recommended IV antibiotics for respiratory infections?

IV Antibiotics for Respiratory Infections

The choice of IV antibiotics depends critically on whether you are treating community-acquired pneumonia (CAP) or hospital-acquired pneumonia (HAP), with severity of illness and risk factors for resistant organisms determining the specific regimen.

Community-Acquired Pneumonia (CAP) - Hospitalized Patients

Non-ICU Patients (Moderate Severity)

For hospitalized patients with CAP not requiring ICU admission, use either combination therapy with a beta-lactam plus macrolide OR monotherapy with a respiratory fluoroquinolone. 1, 2

Recommended regimens include:

• Ceftriaxone 1-2 g IV every 24 hours PLUS azithromycin 1, 2, 3
• Cefotaxime 1-2 g IV every 8 hours PLUS macrolide 1
• Ampicillin-sulbactam PLUS macrolide 1
• Levofloxacin 750 mg IV daily (monotherapy) 1, 2
• Moxifloxacin 400 mg IV daily (monotherapy) 1, 2

Important dosing consideration: Ceftriaxone 1 g daily is as effective as 2 g daily for CAP in regions with low penicillin resistance, with lower rates of C. difficile infection and shorter hospital stays. 3 However, use 2 g daily for severe pneumonia or high-level penicillin resistance. 2

ICU Patients (Severe CAP)

For severe CAP requiring ICU admission, use combination therapy with a beta-lactam PLUS either a macrolide OR respiratory fluoroquinolone. 1, 2

Standard regimens (no Pseudomonas risk):

• Non-antipseudomonal cephalosporin III (ceftriaxone or cefotaxime) PLUS macrolide 1
• Moxifloxacin or levofloxacin 750 mg daily ± cephalosporin III 1

Pseudomonas coverage (if risk factors present):

• Antipseudomonal cephalosporin (cefepime 2 g IV q8h or ceftazidime) OR piperacillin-tazobactam 4.5 g IV q6h OR meropenem 1 g IV q8h 1
• PLUS ciprofloxacin 400 mg IV q8h 1
• OR PLUS macrolide + aminoglycoside (gentamicin 5-7 mg/kg daily, tobramycin 5-7 mg/kg daily, or amikacin 15-20 mg/kg daily) 1

Critical caveat: If using ceftazidime for Pseudomonas coverage, add penicillin G for adequate Streptococcus pneumoniae coverage, as ceftazidime has poor antipneumococcal activity. 1

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

Low Risk Patients (No MRSA Risk, Not High Mortality Risk)

Use monotherapy with one of the following: 1

• Piperacillin-tazobactam 4.5 g IV q6h 1, 4
• Cefepime 2 g IV q8h 1
• Levofloxacin 750 mg IV daily 1
• Imipenem 500 mg IV q6h 1
• Meropenem 1 g IV q8h 1

MRSA Risk Factors Present (But Not High Mortality Risk)

Use the same gram-negative coverage as above PLUS MRSA coverage: 1

• Vancomycin 15 mg/kg IV q8-12h (target trough 15-20 mg/mL; consider loading dose 25-30 mg/kg for severe illness) 1
• OR Linezolid 600 mg IV q12h 1

MRSA risk factors include: IV antibiotic use within 90 days, unit where >20% of S. aureus isolates are methicillin-resistant, or prior MRSA detection. 1

High Mortality Risk OR Recent IV Antibiotics (Within 90 Days)

Use TWO antipseudomonal agents from different classes (avoid two beta-lactams) PLUS MRSA coverage: 1

Choose TWO from:

• Piperacillin-tazobactam 4.5 g IV q6h 1
• Cefepime or ceftazidime 2 g IV q8h 1
• Levofloxacin 750 mg IV daily OR ciprofloxacin 400 mg IV q8h 1
• Imipenem 500 mg IV q6h OR meropenem 1 g IV q8h 1
• Aminoglycoside (amikacin 15-20 mg/kg, gentamicin 5-7 mg/kg, or tobramycin 5-7 mg/kg IV daily) 1
• Aztreonam 2 g IV q8h 1

PLUS MRSA coverage:

• Vancomycin 15 mg/kg IV q8-12h (target trough 15-20 mg/mL) 1
• OR Linezolid 600 mg IV q12h 1

High mortality risk factors: Need for ventilatory support due to pneumonia or septic shock. 1

Special Situations

Aspiration Pneumonia

For hospital ward patients admitted from home: 1

• Beta-lactam/beta-lactamase inhibitor (ampicillin-sulbactam or piperacillin-tazobactam) 1
• OR Clindamycin 1
• OR Moxifloxacin 1

For ICU patients or nursing home residents: 1

• Clindamycin PLUS cephalosporin 1

Nosocomial Pneumonia with Pseudomonas aeruginosa

For nosocomial pneumonia, use piperacillin-tazobactam 4.5 g IV q6h PLUS an aminoglycoside, with continuation of aminoglycoside if P. aeruginosa is isolated. 4 The FDA-approved dosing for nosocomial pneumonia is higher than for other indications. 4

Treatment Duration

Limit treatment to 5-8 days for responding patients with CAP. 1, 2 Biomarkers like procalcitonin may guide shorter durations. 1

For HAP/VAP, treat for 7-14 days depending on severity and pathogen. 1, 4

Extend to 14-21 days ONLY for: 1, 2

• Legionella pneumophila infection
• Staphylococcus aureus pneumonia
• Gram-negative enteric bacilli pneumonia

Transition to Oral Therapy

Switch to oral antibiotics when clinical stability is achieved: resolution of vital sign abnormalities, ability to eat, and normal mentation. 1, 2 This approach is safe even in severe pneumonia. 1 Most patients do not require continued hospitalization after switching to oral therapy. 1

Critical Pitfalls to Avoid

Never use macrolide monotherapy for hospitalized CAP patients - combination therapy with beta-lactam is essential for adequate pneumococcal coverage. 2

Do not use ceftazidime alone for CAP - it has poor activity against S. pneumoniae and requires addition of penicillin G. 1

Avoid fluoroquinolone monotherapy in patients with recent antibiotic exposure - choose a different antibiotic class to reduce resistance risk. 2

For HAP with high mortality risk, never use monotherapy - dual gram-negative coverage plus MRSA coverage is mandatory. 1