What is the recommended dosing regimen for Unasyn (Ampicillin-Sulbactam) for the treatment of intra-abdominal abscesses?

Ampicillin-Sulbactam (Unasyn) Dosing for Intra-abdominal Abscesses

The recommended dosing regimen for Unasyn (Ampicillin-Sulbactam) for the treatment of intra-abdominal abscesses in adults is 3 grams (2 grams ampicillin plus 1 gram sulbactam) administered intravenously every 6 hours for 4-7 days, with duration based on adequate source control. 1

Adult Dosing

• The FDA-approved adult dosage of Unasyn ranges from 1.5 grams to 3 grams every 6 hours, with the 3-gram dose (2 grams ampicillin/1 gram sulbactam) being most appropriate for serious infections like intra-abdominal abscesses 1
• Unasyn should be administered by slow intravenous injection over at least 10-15 minutes or as an infusion over 15-30 minutes in greater dilutions with 50-100 mL of compatible diluent 1
• The total daily dose of sulbactam should not exceed 4 grams per day 1
• Treatment duration should be limited to 4-7 days if adequate source control is achieved through drainage 2

Source Control Considerations

• Percutaneous drainage is recommended for localized abscesses, particularly those larger than 6.5 cm in diameter 3
• Patients with smaller abscesses (average diameter of 4 cm) may respond to antibiotic therapy alone 3
• Patients with fever >101.2°F at admission are more likely to require percutaneous drainage in addition to antibiotics 3
• For optimal treatment outcomes, both appropriate antibiotic selection and prompt drainage are essential 4

Special Populations

Pediatric Patients

• For children 1 year of age or older, the recommended daily dose is 300 mg/kg/day administered intravenously in equally divided doses every 6 hours (corresponding to 200 mg ampicillin/100 mg sulbactam per kg per day) 1
• Children weighing 40 kg or more should receive adult dosing 1
• Intravenous therapy should not routinely exceed 14 days 1

Renal Impairment

• Dosing adjustment is required based on creatinine clearance 1:
  • CrCl ≥30 mL/min: 1.5-3 grams every 6-8 hours
  • CrCl 15-29 mL/min: 1.5-3 grams every 12 hours
  • CrCl 5-14 mL/min: 1.5-3 grams every 24 hours

Alternative Regimens

• For patients with beta-lactam allergies, alternative regimens should be considered, such as eravacycline 1 mg/kg every 12 hours 2
• In cases of suspected or confirmed resistant pathogens, consider carbapenems (e.g., ertapenem 1g every 24 hours) 2
• For critically ill patients with intra-abdominal abscesses, broader coverage may be warranted with regimens such as meropenem 1g every 6-8 hours 2

Clinical Pearls and Pitfalls

• Unasyn reaches peak serum levels within 15 minutes to 1 hour after a 15-minute IV infusion 5
• Clinical studies suggest that a 3-day Ertapenem regimen may be more effective than a 3-day Unasyn regimen for localized intra-abdominal infections of mild to moderate severity 6
• Antibiotic concentrations within abscesses vary by drug; piperacillin/tazobactam and metronidazole generally achieve adequate concentrations in all but the largest abscesses 4
• For abscesses with ≥3 identified organisms, clinical failure rates are significantly higher (58% vs 13%), suggesting the need for broader coverage or longer treatment 4
• Patients who have ongoing signs of infection beyond 7 days of antibiotic treatment warrant further diagnostic investigation 2