What is the recommended dosage of Unasyn (ampicillin/sulbactam) for an adult patient with an open fracture?

Antibiotic Dosing for Open Fractures

For adult patients with open fractures, administer Unasyn (ampicillin/sulbactam) 3 grams IV every 6 hours, which provides 2 grams ampicillin plus 1 gram sulbactam per dose. 1, 2

Standard Dosing Protocol

The recommended adult dosage ranges from 1.5 to 3 grams every 6 hours, with the 3-gram dose (2g ampicillin/1g sulbactam) being appropriate for severe infections like open fractures. 2

• The total sulbactam dose should not exceed 4 grams per day 2
• Administer via slow IV injection over 10-15 minutes, or dilute in 50-100 mL compatible diluent and infuse over 15-30 minutes 2
• Peak serum levels are reached within 15 minutes to 1 hour after IV infusion 3

Rationale for Open Fracture Coverage

Antibiotic prophylaxis is strongly recommended in open fractures to decrease septic complications, as these are contaminated wounds requiring broad-spectrum coverage against both gram-positive and gram-negative organisms. 1

• Ampicillin/sulbactam achieves excellent tissue penetration, reaching bone concentrations of 21.8 mg/kg ampicillin and 4.9 mg/kg sulbactam within 15 minutes of infusion 4
• Tissue concentrations remain above MIC levels for common pathogens for at least 2 hours in skin, fat, muscle, and bone 4, 5
• The combination provides coverage against staphylococci, streptococci, and gram-negative bacilli including E. coli and Proteus species 1, 6

Duration of Therapy

Continue antibiotic therapy for 3 days for Type I and II open fractures, and 5 days for Type III open fractures. 7

• When secondary procedures are performed (bone grafting, ORIF, soft tissue transfers), add an additional 72 hours of therapy 7
• The course of IV therapy should not routinely exceed 14 days 2

Dosage Adjustments for Renal Impairment

Reduce dosing frequency in patients with renal dysfunction, as ampicillin and sulbactam elimination kinetics are similarly affected. 2

• Creatinine clearance ≥30 mL/min: 1.5-3g every 6-8 hours 2
• Creatinine clearance 15-29 mL/min: 1.5-3g every 12 hours 2
• Creatinine clearance 5-14 mL/min: 1.5-3g every 24 hours 2

Critical Considerations for Combination Therapy

If gentamicin is added for Type III open fractures (particularly with soil contamination), reconstitute and administer separately from ampicillin/sulbactam due to in vitro inactivation of aminoglycosides by aminopenicillins. 2

• Gentamicin dosing should be 5 mg/kg/day for optimal peak concentrations 1, 8
• Continue gentamicin for 24-48 hours after definitive wound closure, not exceeding 72 hours total 8

Common Pitfalls to Avoid

Do not use ampicillin/sulbactam monotherapy beyond the recommended duration without reassessing for established infection. 7

• If antibiotic therapy continues after the initial period, select antimicrobials based on culture and sensitivities of original organisms 7
• Ensure adequate surgical debridement, as antibiotics alone cannot sterilize contaminated fracture wounds 1