What are the different types of intravenous (IV) antibiotics and their uses?

IV Antibiotics and Their Clinical Applications

The most appropriate IV antibiotics should be selected based on the suspected pathogen, infection site, and patient factors, with beta-lactams (including penicillins, cephalosporins, and carbapenems) forming the backbone of treatment for most serious infections. 1

Beta-Lactam Antibiotics

Penicillins

• Penicillin G: First-line for streptococcal infections, including Streptococcus pneumoniae with penicillin MIC <2 1
• Ampicillin/Amoxicillin: Used for susceptible streptococcal and enterococcal infections 1
• Oxacillin/Nafcillin: Specific for methicillin-susceptible Staphylococcus aureus (MSSA) infections 1
• Piperacillin-tazobactam: Broad-spectrum coverage for mixed infections, including Pseudomonas and anaerobes; commonly used for intra-abdominal infections 1

Cephalosporins

• First-generation (cefazolin): Used for MSSA infections, surgical prophylaxis for clean procedures 1
• Second-generation (cefuroxime): Active against respiratory pathogens including Haemophilus influenzae 1
• Third-generation (ceftriaxone, cefotaxime): Extended gram-negative coverage, used for meningitis, pneumonia, and complicated UTIs 1
• Fourth-generation (cefepime): Extended spectrum including Pseudomonas aeruginosa 1

Carbapenems

• Imipenem/cilastatin: Broad-spectrum for serious mixed infections including respiratory, intra-abdominal, skin/soft tissue, and bacteremia 2
• Meropenem: Similar to imipenem but with activity against gram-positive, gram-negative, and anaerobic bacteria 3
• Ertapenem: Once-daily dosing, lacks Pseudomonas coverage 1

Non-Beta-Lactam Antibiotics

Aminoglycosides

• Gentamicin/Tobramycin: Used for serious gram-negative infections, often in combination with beta-lactams 1
• Amikacin: Reserved for resistant gram-negative infections 1
• Typically dosed once daily to minimize nephrotoxicity 1

Glycopeptides

• Vancomycin: Primary agent for MRSA infections and resistant gram-positive organisms 1
• Teicoplanin: Alternative to vancomycin with similar spectrum but less nephrotoxicity 1

Fluoroquinolones

• Ciprofloxacin: Strong gram-negative coverage including Pseudomonas 1
• Levofloxacin/Moxifloxacin: Respiratory fluoroquinolones with improved gram-positive and atypical coverage 1

Other Important Classes

• Linezolid: For resistant gram-positive infections including MRSA and VRE 1
• Daptomycin: For MRSA bacteremia and right-sided endocarditis 1
• Metronidazole: Specific for anaerobic coverage, often combined with other agents 1

Clinical Applications by Infection Type

Skin and Soft Tissue Infections

• Cellulitis/Abscess: Cefazolin for MSSA; vancomycin for suspected MRSA 1
• Necrotizing fasciitis: Combination therapy with piperacillin-tazobactam plus vancomycin, or a carbapenem 1
• Animal/human bites: Ampicillin-sulbactam, piperacillin-tazobactam, or carbapenem 1

Respiratory Infections

• Community-acquired pneumonia: Ceftriaxone plus macrolide or respiratory fluoroquinolone monotherapy 1
• Hospital-acquired pneumonia: Anti-pseudomonal beta-lactam (piperacillin-tazobactam, cefepime) plus vancomycin if MRSA risk 1

Intra-abdominal Infections

• Peritonitis/abscess: Piperacillin-tazobactam, carbapenem, or ceftriaxone plus metronidazole 1
• Biliary infections: Similar coverage with emphasis on enterococci and gram-negative organisms 1

Bloodstream Infections

• Gram-positive bacteremia: Vancomycin for MRSA, nafcillin/oxacillin for MSSA 1
• Gram-negative bacteremia: Ceftriaxone, piperacillin-tazobactam, or carbapenem based on severity 1
• Endocarditis: Prolonged therapy with penicillin plus gentamicin for streptococci; vancomycin for MRSA 1

Urinary Tract Infections

• Complicated UTIs: Ceftriaxone, fluoroquinolone, or aminoglycoside 1
• Pyelonephritis: Similar coverage with emphasis on gram-negative pathogens 2

Special Considerations

Neutropenic Fever

• Initial empiric therapy: Anti-pseudomonal beta-lactam (piperacillin-tazobactam, cefepime, carbapenem) 1
• Add vancomycin if line infection or soft tissue infection suspected 1
• Add antifungal if persistent fever despite antibiotics 1

Multi-drug Resistant Organisms

• Carbapenem-resistant Enterobacterales: Ceftazidime-avibactam, polymyxin-based combinations 1
• MRSA: Vancomycin, linezolid, or daptomycin 1
• VRE: Linezolid or daptomycin 1

Pediatric Considerations

• Dosing based on weight and age-specific pharmacokinetics 1
• Avoid tetracyclines in young children due to dental staining 1
• Carbapenems preferred over fluoroquinolones for serious gram-negative infections 1

Common Pitfalls to Avoid

• Failing to adjust dosing for renal/hepatic impairment 1
• Prolonged IV therapy when oral switch is appropriate 4
• Inadequate source control relying solely on antibiotics 1
• Not considering local resistance patterns when selecting empiric therapy 1
• Overuse of broad-spectrum agents when narrower options would suffice 5