What is the recommended dose of vancomycin IV for an adult patient with a skin infection, who is currently on Augmentin (amoxicillin-clavulanate)?

Vancomycin IV Dosing for Skin Infections in Adults

For an adult patient with a skin infection, vancomycin should be dosed at 15-20 mg/kg (actual body weight) IV every 8-12 hours, not exceeding 2 grams per dose. 1, 2

Standard Dosing Regimen

• Weight-based dosing at 15-20 mg/kg every 8-12 hours is the recommended approach for complicated skin and soft tissue infections (cSSTI) requiring IV vancomycin 1
• For non-obese patients with normal renal function and non-severe infections, traditional fixed doses of 1 gram every 12 hours may be adequate, though weight-based dosing is preferred 2
• The maximum single dose should not exceed 2 grams 2

Loading Dose Considerations

• For seriously ill patients with systemic signs of infection or suspected MRSA, administer a loading dose of 25-30 mg/kg (actual body weight) to rapidly achieve therapeutic concentrations 2
• This loading dose is particularly important in patients with severe cellulitis, purulent infections, or those meeting criteria for systemic inflammatory response syndrome (SIRS) 1
• Prolong the infusion time to at least 2 hours for loading doses and consider antihistamine premedication to prevent red man syndrome 2

Therapeutic Monitoring

• Trough concentrations should be obtained before the fourth or fifth dose (at steady state) 2
• Target trough levels of 15-20 μg/mL for complicated or severe skin infections 1, 2
• For simple, non-severe skin infections in patients with normal renal function who are not obese, trough monitoring may not be required 2
• Monitoring is mandatory for morbidly obese patients, those with renal dysfunction, or fluctuating volumes of distribution 2

Clinical Context and Decision Algorithm

When to use vancomycin for skin infections:

• The patient is already on Augmentin, suggesting either treatment failure or concern for resistant organisms 1
• Vancomycin is indicated when there is suspected or confirmed MRSA, particularly in purulent cellulitis 1
• For non-purulent cellulitis without systemic toxicity, beta-lactams like Augmentin remain first-line; vancomycin should be added only if there is penetrating trauma, evidence of MRSA elsewhere, nasal MRSA colonization, injection drug use, or systemic signs of infection 1

Dosing calculation example:

• For a 70 kg patient: 15 mg/kg × 70 kg = 1,050 mg, round to 1,000 mg every 12 hours
• For an 85 kg patient: 15 mg/kg × 85 kg = 1,275 mg, round to 1,250 mg every 12 hours
• For a 100 kg patient: 20 mg/kg × 100 kg = 2,000 mg every 12 hours (maximum dose)

Important Caveats and Pitfalls

• Fixed 1-gram dosing significantly underdoses most patients, particularly those weighing >70 kg, leading to subtherapeutic levels and potential treatment failure 3, 4
• The pharmacodynamic target is an AUC/MIC ratio >400, which correlates with clinical efficacy 2, 5
• If the vancomycin MIC is ≥2 μg/mL, switch to an alternative agent such as daptomycin (4 mg/kg IV daily), linezolid (600 mg IV/PO twice daily), or ceftaroline (600 mg IV twice daily) 1, 2
• Nephrotoxicity risk increases significantly with trough levels >15 mg/L, especially when combined with other nephrotoxic agents like piperacillin-tazobactam, aminoglycosides, or NSAIDs 2
• Recent evidence suggests AUC-guided dosing (targeting AUC 400-600 mg×hr/L) may be superior to trough-only monitoring for balancing efficacy and minimizing nephrotoxicity 5

Duration of Therapy

• For uncomplicated skin and soft tissue infections: 7-14 days depending on clinical response 1
• For complicated infections with bacteremia: minimum 2 weeks for uncomplicated bacteremia, 4-6 weeks for complicated bacteremia 1
• Reassess the need for continued vancomycin versus transition to oral therapy (if susceptible) or alternative agents based on culture results and clinical improvement 1