• Bacterial infections

Unasyn Generic Name & Formulations

General Description

Ampicillin sodium 1g, sulbactam sodium 0.5g (1.5g vial); or ampicillin sodium 2g, sulbactam sodium 1g (3g vial); IM or IV inj; sodium content 5mEq/g of ampicillin.

Pharmacological Class

Broad-spectrum penicillin + β-lactamase inhibitor.

How Supplied

Vials (1.5g, 3g)—1


Unasyn sterile powder is to be stored at or below 30°C (86°F) prior to reconstitution.


Generic Availability


Mechanism of Action

Ampicillin is similar to benzyl penicillin in its bactericidal action against susceptible organisms during the stage of active multiplication. It acts through the inhibition of cell wall mucopeptide biosynthesis. Ampicillin has a broad spectrum of bactericidal activity against many gram-positive and gram-negative aerobic and anaerobic bacteria. Although sulbactam alone possesses little useful antibacterial activity except against the Neisseriaceae, whole organism studies have shown that sulbactam restores ampicillin activity against beta-lactamase producing strains. In particular, sulbactam has good inhibitory activity against the clinically important plasmid mediated beta-lactamases most frequently responsible for transferred drug resistance. Sulbactam has no effect on the activity of ampicillin against ampicillin susceptible strains. Thus, Unasyn possesses the properties of a broad-spectrum antibacterial and a beta-lactamase inhibitor.

Unasyn Indications


Susceptible skin and skin structure, intraabdominal, gynecologic infections.


For the treatment of infections due to susceptible strains of the designated microorganisms in the following conditions:

  • Skin and skin structure infections caused by beta-lactamase producing strains of Staphylococcus aureus, Escherichia coli, Klebsiella spp. (including K. pneumoniae), Proteus mirabilis, Bacteroides fragilis, Enterobacter spp., and Acinetobacter calcoaceticus.

  • Intra-abdominal infections caused by beta-lactamase producing strains of Escherichia coli, Klebsiella spp. (including K. pneumoniae), Bacteroides spp. (including B. fragilis), and Enterobacter spp.

  • Gynecological infections caused by beta-lactamase producing strains of Escherichia coli, and Bacteroides spp. (including B. fragilis).

While Unasyn is indicated only for the conditions listed above, infections caused by ampicillin-susceptible organisms are also amenable to treatment with Unasyn due to its ampicillin content.

Unasyn Dosage and Administration


Dose is given as ampicillin + sulbactam. Normal renal function (CrCl ≥30mL/min): 1.5–3g IM or IV every 6hrs; CrCl 15–29mL/min: 1.5–3g every 12hrs; CrCl 5–14mL/min: 1.5–3g every 24hrs.


Intraabdominal infections: not established. Dose is given as ampicillin + sulbactam. <1yr: not established. ≥1yr (<40kg): 300mg/kg per day IV in equally divided doses every 6hrs; usual max 14 days. ≥40kg: as adult.

Unasyn Contraindications


History of cholestatic jaundice/hepatic dysfunction due to Unasyn. Penicillin, cephalosporin, or other β-lactam allergy.

Unasyn Boxed Warnings

Not Applicable

Unasyn Warnings/Precautions


Mononucleosis: not recommended. Discontinue if superinfection or hypersensitivity reactions occur, or if skin lesions progress. Hepatic impairment; monitor LFTs regularly. Pregnancy. Nursing mothers.



  • Serious and occasionally fatal hypersensitivity (anaphylactic) reactions have been reported. These reactions are more likely in those with a history of penicillin hypersensitivity and/or hypersensitivity reactions to multiple allergens.

  • Prior to initiation, ask patients carefully regarding any previous hypersensitivity reactions to penicillins, cephalosporins, and other allergens.

  • Discontinue Unasyn and treat appropriately if an allergic reaction occurs.


  • Hepatic dysfunction, including hepatitis and cholestatic jaundice has been associated with the use of Unasyn. Hepatic toxicity is usually reversible.

  • Monitor hepatic function at regular intervals in patients with hepatic impairment.

Severe Cutaneous Adverse Reactions

  • Severe skin reactions may occur including toxic epidermal necrolysis (TEN), Stevens-Johnson syndrome (SJS), dermatitis exfoliative, erythema multiforme, and Acute generalized exanthematous pustulosis (AGEP). 

  • Monitor closely if patients develop a skin rash and discontinue Unasyn if lesions progress.

Clostridium difficile-Associated Diarrhea (CDAD)

  • Consider CDAD in all patients who present with diarrhea after antibacterial drug use.

  • Careful medical history is necessary since CDAD has been reported to occur over two months after the administration.

  • If suspected or confirmed, antibacterial drug use not directed against C. difficile may need to be discontinued. 

Pregnancy Considerations

  • No adequate and well-controlled studies in pregnant women. Unasyn should only be used during pregnancy if clearly needed.

  • Labor and Delivery:

    • It is not known whether the use of Unasyn in humans during labor or delivery has immediate or delayed adverse effects on the fetus, prolongs the duration of labor, or increases the likelihood that forceps delivery or other obstetrical intervention or resuscitation of the newborn will be necessary.

Nursing Mother Considerations

  • Low concentrations of ampicillin and sulbactam are excreted in the milk. 

  • Exercise caution when Unasyn is administered to a nursing woman. 

Pediatric Considerations

For skin and skin structure infections:

  • Safety and efficacy of Unasyn has been established in pediatric patients 1 year of age and older.

For intra-abdominal infections:

  • Safety and efficacy of Unasyn has not been established in pediatric patients.

Unasyn Pharmacokinetics


After a 15-minute IV infusion of ampicillin 2000 mg plus sulbactam 1000 mg:

  • Peak serum levels ranged from: 109 to 150 mcg/mL for ampicillin; 48 to 88 mcg/mL for sulbactam.

After a 15-minute IV infusion of ampicillin 1000 mg plus sulbactam 500 mg:

  • Peak serum levels ranged from: 40 to 71 mcg/mL for ampicillin; 21 to 40 mcg/mL for sulbactam.

After an IM injection of ampicillin 1000 mg plus sulbactam 500 mg:

  • Peak serum levels ranged from: 8 to 37 mcg/mL for ampicillin; 6 to 24 mcg/mL for sulbactam.


  • Ampicillin is ~28% reversibly bound to human serum protein; Sulbactam is ~ 38% reversibly bound to human serum protein.


  • Renal. Half-life: ~1 hour.

Unasyn Interactions


Potentiated by probenecid. Increased incidence of rash with allopurinol. May cause false (+) Clinitest, Benedict's or Fehling's soln.

Unasyn Adverse Reactions

Adverse Reactions

Inj site reactions, diarrhea, rash, blood dyscrasias; C. difficile-associated diarrhea (evaluate if occurs), hypersensitivity or severe skin reactions (eg, SJS, TEN, dermatitis exfoliative, erythema multiforme, AGEP), hepatotoxicity.

Unasyn Clinical Trials

Clinical Trials

Skin and Skin Structure Infections in Pediatric Patients

  • A controlled clinical trial evaluated the efficacy and safety of Unasyn for the treatment of skin and skin structure infections in pediatric patients. Patients received either Unasyn (n=60) or cefuroxime (n=39) intravenously. Results showed similar outcomes between both treatment arms.

Unasyn Note

Not Applicable

Unasyn Patient Counseling

Patient Counseling

  • Advise patients that antibacterial drugs including Unasyn should only be used to treat bacterial infections. These drugs do not treat viral infections.

  • Complete the full course of therapy; skipping doses or not completing therapy may decrease the effectiveness of the treatment and increase the likelihood of drug-resistance bacteria. 

  • Diarrhea is common with antibiotics and usually ends with treatment. If watery, bloody stools develop even as late as 2 months after the last dose of antibiotic, contact a healthcare provider.