Ampicillin + sulbactam !

Ampicillin protected by sulbactam for mixed intra-abdominal, gynaecological and skin infections.

Updated 2026-11-01

Class: Beta-lactams
Enzyme: Bacterial PBPs (ampicillin) and β-lactamases (sulbactam)
ATC code: J01CR01

Also called: ampicillin–sulbactam

Bacterial PBPs (ampicillin) and β-lactamases (sulbactam)Ampicillin + sulbactam

The figure shows sulbactam in the SHV-1 β-lactamase of Klebsiella pneumoniae (E166A variant), trapped as a trans-enamine intermediate in the active site.

Target in 3D: Bacterial PBPs (ampicillin) and β-lactamases (sulbactam). PDB structure 2A3U (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Ampicillin acylates the PBPs, but β-lactamases break it down. Sulbactam, a penicillin sulfone, irreversibly inhibits many of those β-lactamases and restores ampicillin's activity against methicillin-susceptible S. aureus, H. influenzae, enteric bacteria and anaerobes such as Bacteroides. On its own, sulbactam has little useful antibacterial action, except against the Neisseriaceae.

Sulbactam binds the β-lactamase and inactivates it
Ampicillin stays intact and reaches the PBPs
Peptidoglycan cross-linking is blocked
The wall fails and the bacterium lyses

Pharmacokinetics

Absorption: Intravenous or intramuscular only.
Elimination: Both components leave unchanged in the urine; adjusted in kidney failure.
Half-life: About 1 hour for both in healthy people.

Indications

Intra-abdominal infections. Peritonitis →
Gynaecological infections such as endometritis and pelvic inflammatory disease. Pelvic inflammatory disease →
Skin and soft-tissue infections. Cellulitis of the leg →

Adverse effects

Common

Injection-site pain and phlebitis
Diarrhoea, rash
Transient rise in transaminases

Contraindications

History of a serious hypersensitivity reaction (anaphylaxis, Stevens–Johnson syndrome) to any penicillin or other β-lactam
Previous cholestatic jaundice or liver dysfunction linked to ampicillin + sulbactam

Key interactions

Probenecid: Reduces tubular secretion: higher and longer-lasting β-lactam levels.
Allopurinol: Raises the rate of rash with aminopenicillins.
Aminoglycosides (in the same mixture): Ampicillin inactivates them in vitro; they are reconstituted and given separately.

What is monitored

Liver tests if jaundice or liver disease
Kidney function and blood count in long courses

Administration and safety

Intravenous (slow injection or infusion) or deep intramuscular.
Do not mix with aminoglycosides in the same syringe or bag.
Do not confuse with plain ampicillin: the spectrum is different.

Nursing care

Before the first dose: ask about allergy to penicillins, cephalosporins and other β-lactams, and what the reaction was.
After the first dose, watch for hives, wheeze, low blood pressure or swelling of lips and tongue, with anaphylaxis equipment at hand.
Check the IV site for phlebitis.
Watch for jaundice, dark urine or itching.
Teach the patient to report watery or bloody diarrhoea, even weeks after the course ends.

Pregnancy and breastfeeding

Animal studies showed no fetal harm and there are no controlled studies in pregnant women; used when clearly needed.

Test yourself

Think of the answer, then tap the question to see it.

Why is sulbactam not used alone as an antibiotic?

Because on its own it has little useful antibacterial activity (except against the Neisseriaceae); its job is to inhibit the β-lactamases that would destroy ampicillin.

Why does ampicillin + sulbactam cover anaerobes such as Bacteroides while ampicillin alone does not?

Because Bacteroides makes β-lactamases that destroy ampicillin; sulbactam inhibits them.

Which liver history rules out the combination?

Previous cholestatic jaundice or liver dysfunction linked to ampicillin + sulbactam.

Add to my cards (3)

← Back to the class: Beta-lactams

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Ampicillin and Sulbactam Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); DailyMed - AMPICILLIN AND SULBACTAM injection, powder, for solution (DailyMed (U.S. National Library of Medicine), 2026); RCSB PDB - 2A3U: Crystal structure of sulbactam bound to E166A variant of SHV-1 beta-lactamase (RCSB Protein Data Bank, 2026); Farmacología básica y clínica (Katzung), cap. 43 (McGraw Hill, 2025).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.