What is the dose of Unasyn (Ampicillin/Sulbactam) for a patient with normal renal function?

Unasyn (Ampicillin/Sulbactam) Dosing for Normal Renal Function

For adults with normal renal function, the standard dose of Unasyn is 1.5 to 3 grams (1 to 2 grams ampicillin plus 0.5 to 1 gram sulbactam) administered intravenously every 6 hours, with a maximum daily dose of 12 grams (8 grams ampicillin plus 4 grams sulbactam). 1

Standard Adult Dosing Regimens

Intravenous Administration:

• Mild to moderate infections: 1.5 grams (1 gram ampicillin/0.5 gram sulbactam) IV every 6 hours 1
• Moderate to severe infections: 3 grams (2 grams ampicillin/1 gram sulbactam) IV every 6 hours 1, 2
• Maximum daily dose: 12 grams total (8 grams ampicillin/4 grams sulbactam) 1

Intramuscular Administration:

• 1.5 grams (1 gram ampicillin/0.5 gram sulbactam) IM can be used when IV access is not available 1
• Peak serum levels after IM injection range from 8 to 37 mcg/mL for ampicillin and 6 to 24 mcg/mL for sulbactam 1

Pharmacokinetic Considerations

Timing and Peak Levels:

• Peak serum concentrations are achieved immediately after a 15-minute IV infusion 1
• After 2 grams ampicillin/1 gram sulbactam IV: peak ampicillin levels reach 109-150 mcg/mL and sulbactam levels reach 48-88 mcg/mL 1
• After 1 gram ampicillin/0.5 gram sulbactam IV: peak ampicillin levels reach 40-71 mcg/mL and sulbactam levels reach 21-40 mcg/mL 1

Elimination:

• Mean serum half-life is approximately 1 hour for both ampicillin and sulbactam in healthy volunteers 1
• 75-85% of both drugs are excreted unchanged in urine during the first 8 hours after administration 1
• Ampicillin is approximately 28% protein-bound and sulbactam is approximately 38% protein-bound 1

Pediatric Dosing

For pediatric patients with normal renal function:

• Standard dose: 50 to 75 mg/kg body weight (combined ampicillin/sulbactam) administered IV every 6 hours 1
• Peak serum concentrations after 15-minute infusion: 82-446 mcg/mL for ampicillin and 44-203 mcg/mL for sulbactam 1
• Mean half-life is approximately 1 hour, similar to adults 1

Clinical Application by Infection Type

Urogenital Infections:

• Average daily dose of 6 to 9 grams total (administered as divided doses every 6 hours) for 7-10 days 2
• Clinical and bacteriological efficacy of 95% demonstrated in acute pyelonephritis 2
• Excellent efficacy against gram-positive flora and E. coli; satisfactory results against Proteus species 2

Oral Formulation (Sultamicillin):

• For mild to moderate infections when oral therapy is appropriate: 375 mg tablets twice daily 3
• Pediatric oral dose: 50 mg/kg per day divided into doses 4
• Mean treatment duration: 7.4 days (range 4-14 days) 4

Important Clinical Considerations

Tissue Penetration:

• Unasyn achieves therapeutic levels in peritoneal fluid, blister fluid, intestinal mucosa, and appendix 1
• Both ampicillin and sulbactam penetrate into cerebrospinal fluid in the presence of inflamed meninges 1

Administration Technique:

• Administer IV infusion over 15 minutes to achieve optimal peak concentrations 1, 5
• When using IM route, expect pain at injection site as the most common adverse effect 2

Common Pitfall to Avoid:

• Do not reduce dosing frequency in patients with normal renal function—the every 6-hour interval is essential to maintain therapeutic levels given the 1-hour half-life 1
• Ensure adequate hydration to support renal elimination of 75-85% of the drug 1