What is the recommended dose of Ancef (cefazolin) for a patient with a gram-positive cocci skin infection weighing 115kg?

Cefazolin Dosing for 115kg Patient with Gram-Positive Skin Infection

For a 115kg patient with a gram-positive cocci skin infection, the appropriate dose of Ancef (cefazolin) is 2g IV every 8 hours. 1, 2

Dosing Rationale

• Standard cefazolin dosing for skin and soft tissue infections (SSTIs) caused by gram-positive cocci is 1g every 8 hours IV for adults 3
• For patients with high body weight (>120kg), higher dosing of cefazolin up to 2g every 8 hours is safe and effective for treating SSTIs 2
• The FDA label for cefazolin indicates that doses up to 12g per day have been used in rare instances for severe infections 1
• At 115kg, the patient approaches the threshold where standard dosing may be insufficient for optimal tissue penetration 4

Pharmacokinetic Considerations

• Cefazolin penetration into interstitial fluid of infected tissue can be variable, with a median penetration ratio of 0.80 4
• For patients with higher body weight, standard dosing may result in suboptimal tissue concentrations 5, 4
• Monte Carlo simulations suggest that 2g every 8 hours provides better probability of target attainment for the pharmacodynamic target of 50% fT>MIC at the clinical breakpoint 4

Clinical Efficacy for Skin Infections

• Cefazolin is a first-line agent for methicillin-susceptible Staphylococcus aureus (MSSA) skin infections 3
• For gram-positive skin infections, cefazolin has excellent activity against Staphylococcus and Streptococcus species 3
• Higher doses ensure adequate tissue concentrations even with the potential for reduced penetration in infected tissues 5

Important Considerations

• Renal function should be assessed before initiating therapy, as dosage adjustments are needed for patients with impaired renal function 1
• For patients with creatinine clearance of 55 mL/min or greater, full doses can be given 1
• If the patient has moderate renal impairment (CrCl 35-54 mL/min), the dosing interval should be extended to at least 8 hours 1
• Duration of therapy for skin infections typically ranges from 7-14 days depending on clinical response 3

Alternative Options

• If the patient has a severe penicillin allergy, vancomycin 30 mg/kg/day in 2 divided doses IV would be the appropriate alternative 3
• If MRSA is suspected or confirmed, alternative agents such as vancomycin, linezolid, or daptomycin should be considered 3
• For patients unable to receive IV therapy, oral options after initial IV therapy may include cephalexin (for MSSA) or appropriate oral agents based on culture results 3

The 2g every 8 hours dosing regimen balances the need for adequate tissue concentrations in this high-body-weight patient while maintaining safety, as studies have shown that high-dose cefazolin (up to 9g/day) is well-tolerated in patients with high body weight 2.