What are the common IV antibiotic dosages for adults?

Common IV Antibiotic Dosages for Adults

For critically ill adults requiring IV antibiotics, vancomycin should be dosed at 15-20 mg/kg/dose every 8-12 hours (targeting trough levels of 15-20 mg/mL for serious infections), while beta-lactams like cefepime require 2g every 8 hours for severe infections, and linezolid is standardized at 600 mg every 12 hours regardless of renal function. 1, 2, 3

Glycopeptides

Vancomycin

• Standard dosing: 15-20 mg/kg/dose IV every 8-12 hours 1
• Loading dose for seriously ill patients: 25-30 mg/kg 1
• Target trough levels: 15-20 mg/mL for serious infections (bacteremia, endocarditis, pneumonia, meningitis) 2
• Common pitfall: Using 1g daily dosing is inadequate for severe infections and risks treatment failure 2

Teicoplanin

• Loading: 6-12 mg/kg/dose IV every 12 hours for 3 doses 1
• Maintenance: 6-12 mg/kg/dose IV once daily 1
• For complicated bacteremia: May require 3-6 loading doses before transitioning to maintenance 1

Oxazolidinones

Linezolid

• Standard dosing: 600 mg IV or PO every 12 hours 1, 3
• Key advantage: No dose adjustment needed for renal or hepatic impairment, and IV-to-PO conversion requires no dose change 3
• Duration limit: Not evaluated beyond 28 days in controlled trials 3
• Monitoring: Weekly CBC recommended, especially if treatment exceeds 2 weeks due to myelosuppression risk 3

Beta-Lactams

Cefepime

• Severe infections/high mortality risk: 2g IV every 8 hours 2
• Standard infections: 1-2g IV every 8-12 hours (per general practice)
• Administration: Can be given as IV push over 3-5 minutes or infusion over 30 minutes 4

Meropenem

• Complicated skin/soft tissue infections: 500 mg IV every 8 hours 5
• Intra-abdominal infections: 1g IV every 8 hours 5
• Pseudomonas aeruginosa coverage: 1g IV every 8 hours 5
• Administration options: 15-30 minute infusion OR 3-5 minute IV bolus 5

Piperacillin-Tazobactam

• Standard dosing: 3.375-4.5g IV every 6-8 hours (per general practice)
• Extended infusion preferred: 4-6 hour infusions optimize time above MIC for time-dependent killing 6

Lipopeptides

Daptomycin

• Complicated skin/soft tissue infections: 4 mg/kg IV once daily 1
• Bacteremia/endocarditis: 6 mg/kg IV once daily 1
• Some experts recommend: 6-10 mg/kg IV once daily for complicated bacteremia 1
• Contraindication: Never use for pneumonia (inactivated by pulmonary surfactant) 7

Lincosamides

Clindamycin

• IV dosing: 600 mg IV every 8 hours 1
• Alternative: 300-450 mg PO every 8 hours for less severe infections 1
• Maximum daily dose: Not to exceed 40 mg/kg/day in pediatrics (adult equivalent consideration) 1
• Caveat: Higher risk of Clostridioides difficile infection compared to other oral agents 1

Aminoglycosides

Gentamicin/Tobramycin

• Endocarditis (adjunctive): 1 mg/kg IV every 8 hours 1
• Extended interval dosing preferred: Maximizes concentration-dependent killing and minimizes nephrotoxicity 6
• Monitoring: Peak and trough levels essential, especially in critically ill patients 8

Fluoroquinolones

Ciprofloxacin

• Standard dosing: 400 mg IV every 8-12 hours (per general practice)
• Not recommended for IV push: Limited data support this route 4

Levofloxacin

• Standard dosing: 500-750 mg IV once daily (per general practice)
• Advantage: Once-daily dosing with excellent bioavailability 8

Critical Dosing Principles

Loading Doses

• Essential in sepsis: Loading dose is independent of renal function and depends only on volume of distribution 6
• Vancomycin: 25-30 mg/kg for seriously ill patients 1, 2
• Rationale: Increased extravascular space in early sepsis requires higher initial doses of hydrophilic agents 6

Time-Dependent vs. Concentration-Dependent Antibiotics

• Time-dependent (beta-lactams): Optimize time above MIC with extended or continuous infusions (4-6 hours minimum) 6
• Concentration-dependent (aminoglycosides, fluoroquinolones): Use extended interval dosing to maximize peak concentration 6

Renal Adjustment

• Meropenem renal dosing: 5
  • CrCl >50 mL/min: Standard dose every 8 hours
  • CrCl 26-50 mL/min: Standard dose every 12 hours
  • CrCl 10-25 mL/min: Half dose every 12 hours
  • CrCl <10 mL/min: Half dose every 24 hours
• Vancomycin: Requires dose adjustment and therapeutic drug monitoring in renal impairment 2
• Linezolid: No adjustment needed 3

Monitoring Requirements

• Vancomycin: Trough levels before 4th dose, target 15-20 mg/mL for serious infections 2
• Linezolid: Weekly CBC if treatment >2 weeks 3
• Aminoglycosides: Peak and trough levels 8
• Clinical response: Daily reassessment of WBC, temperature, hemodynamics mandatory 2

Common Pitfalls to Avoid

• Delaying dose optimization when clinical deterioration evident (rising WBC, persistent fever) 2
• Using inadequate vancomycin dosing (1g daily) for severe infections 2
• Not obtaining cultures before initiating therapy to guide de-escalation 2
• Continuing combination therapy unnecessarily after susceptibilities available 2
• Ignoring pharmacodynamic principles: Using standard intermittent dosing for beta-lactams when extended infusions would be superior 6