What is the recommended dosage of Unasyn (Ampicillin/Sulbactam) for treating infections?

Unasyn (Ampicillin-Sulbactam) Dosing

The standard adult dose of Unasyn is 1.5 to 3 grams IV every 6 hours, with the total sulbactam component not exceeding 4 grams per day. 1

Standard Adult Dosing

• 1.5 grams (1g ampicillin/0.5g sulbactam) to 3 grams (2g ampicillin/1g sulbactam) IV every 6 hours is the FDA-approved dosing range 1
• Administer by slow IV injection over 10-15 minutes, or as an infusion in 50-100 mL compatible diluent over 15-30 minutes 1
• The maximum total sulbactam dose should not exceed 4 grams daily 1
• IM administration is also approved, given by deep intramuscular injection 1

Pediatric Dosing (≥1 Year of Age)

• 300 mg/kg/day IV (total ampicillin + sulbactam content) divided every 6 hours is the standard pediatric dose 1
• This corresponds to 200 mg/kg/day ampicillin plus 100 mg/kg/day sulbactam 1
• Children weighing ≥40 kg should receive adult dosing 1
• Maximum sulbactam dose should not exceed 4 grams per day 1
• IM administration safety and efficacy have not been established in pediatric patients 1
• Treatment duration should not routinely exceed 14 days IV 1

High-Dose Regimens for Severe/Resistant Infections

For severe infections or multidrug-resistant organisms (particularly Acinetobacter baumannii), higher doses of 9-12 grams sulbactam per day are recommended. 2, 3

• 9-12 g/day sulbactam divided into 3-4 doses for severe infections caused by organisms with MIC ≤4 mg/L 2, 3
• Administer as 4-hour extended infusions to optimize pharmacokinetic/pharmacodynamic properties 2, 3
• This translates to approximately 3-4 grams sulbactam every 8 hours 3

Clinical Context for High-Dose Therapy

• High-dose sulbactam is particularly effective for carbapenem-resistant Acinetobacter baumannii (CRAB) infections 2, 3
• Clinical outcomes with high-dose sulbactam for severe A. baumannii infections are comparable to imipenem 2
• Sulbactam demonstrates lower nephrotoxicity rates compared to colistin, making it preferable for susceptible strains 2, 3

Specific Infection Dosing

Endocarditis (Adults)

• 12 g/day IV in 4 equally divided doses (3g every 6 hours) combined with gentamicin 3 mg/kg/day for 4-6 weeks 4
• For HACEK endocarditis: 12 g/24 hours IV in 4 divided doses for 4 weeks (native valve) or 6 weeks (prosthetic valve) 4

Endocarditis (Pediatric)

• 300 mg/kg/day IV in 4-6 equally divided doses for 4-6 weeks 4

Complicated Intra-Abdominal Infections (Pediatric)

• 200 mg/kg/day IV divided every 6 hours 4

Surgical Site Infections

• 3 grams every 6 hours IV when used in combination with gentamicin or tobramycin 5 mg/kg every 24 hours for infections involving intestinal or genitourinary tract 2

Renal Impairment Dosing

Dosing frequency must be reduced in renal impairment while maintaining the same individual dose range (1.5-3 grams). 1

• CrCl ≥30 mL/min: 1.5-3 grams every 6-8 hours 1
• CrCl 15-29 mL/min: 1.5-3 grams every 12 hours 1
• CrCl 5-14 mL/min: 1.5-3 grams every 24 hours 1

The elimination kinetics of ampicillin and sulbactam are similarly affected by renal impairment, maintaining a constant ratio 1

Common Pitfalls to Avoid

• Underdosing for resistant organisms: Standard doses (≤6 g/day sulbactam) may be insufficient for severe infections caused by multidrug-resistant pathogens 3
• Not using extended infusions for high-dose therapy: 4-hour infusions are critical for optimizing efficacy and safety when using 9-12 g/day sulbactam 2, 3
• Exceeding maximum sulbactam dose: Never exceed 4 grams sulbactam per day in standard dosing (this limit does not apply to high-dose regimens for resistant organisms) 1
• Ignoring local resistance patterns: Sulbactam efficacy depends on MIC values; verify susceptibility testing shows MIC ≤4 mg/L before selecting sulbactam-based therapy 2, 3
• Using IM route in pediatrics without established safety data: Stick to IV administration in children 1