Ampicillin and Sulbactam
Ampicillin sodium and sulbactam sodium
Also known as: Ampibactan · Bacimex · Begalin-P · Bethacil · Comabactan · Galotam · Loricin · Sulam · Sulperazon · Synergistin · Unacid · Unacim · Unasyna
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For respiratory infections | 50 mg/kg (combined) IV q8h | IV | q8h | — | 🌎 NA |
| For respiratory infections | 20 mg/kg IV or IM q6-8h | IV/IM | q6-8h | — | 🌎 NA |
| As adjunctive treatment of serious bite wounds | 30-50 mg/kg q8h IV | IV | q8h | — | 🌎 NA |
| For intra-abdominal infections | 20 mg/kg IV or IM q6-8h | IV/IM | q6-8h | — | 🌎 NA |
- For intra-abdominal infections: Extrapolation of human dose with limited studies in dogs and cats
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For respiratory infections using ampicillin/sulbactam (Unasyn®) | 50 mg/kg (combined) IV q8h | IV | q8h | — | 🌎 NA |
| As adjunctive treatment of serious bite wounds | 30-50 mg/kg q8h IV | IV | q8h | — | 🌎 NA |
| For intra-abdominal infections | 20 mg/kg IV or IM q6-8h | IV/IM | q6-8h | — | 🌎 NA |
- For intra-abdominal infections: Extrapolation of human dose with limited studies in dogs and cats
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Ampicillin/sulbactam is a parenteral potentiated aminopenicillin. It combines the broad-spectrum bactericidal activity of ampicillin with sulbactam, a beta-lactamase inhibitor.
- Spectrum of Activity: Effective against many beta-lactamase-producing strains of E. coli, Pasteurella spp., Staphylococcus spp., Klebsiella, and Proteus. Also covers anaerobes like Clostridium, Bacteroides, Fusobacterium, and Peptostreptococcus.
- Clinical Utility: Primarily used in dogs and cats when oral amoxicillin/clavulanate is not viable (e.g., patient is NPO, critically ill, or vomiting) or when high parenteral concentrations are required for severe infections like sepsis, pneumonia, or serious bite wounds.
- Limitations: Ineffective against Pseudomonas aeruginosa and certain Type I beta-lactamase producers (Citrobacter, Enterobacter, Serratia).
Clinical Pearl: On a mg-for-mg basis, clavulanic acid is a more potent beta-lactamase inhibitor than sulbactam, but sulbactam offers advantages such as reduced likelihood of inducing chromosomal beta-lactamases, greater tissue penetration, and greater stability.
Mechanism of action
- Ampicillin binds to penicillin-binding proteins (PBPs) located inside the bacterial cell wall → inhibits the third and final stage of bacterial cell wall synthesis → cell lysis and death.
- Sulbactam irreversibly binds to and inactivates beta-lactamases (Richmond-Sykes types II-VI) → protects the beta-lactam ring of ampicillin from enzymatic hydrolysis.
- Note: Sulbactam has weak intrinsic antibacterial activity against certain organisms (Neisseria, Moraxella, Bacteroides) by binding to specific PBPs, providing a synergistic effect when combined with ampicillin.
Safety & warnings
Contraindications
- Patients with a history of severe hypersensitivity (e.g., anaphylaxis) to penicillins
Adverse effects
- Pain at intramuscular injection sites
- Thrombophlebitis (with intravenous injection)
- Hypersensitivity reactions (including severe anaphylaxis, particularly after IV administration)
- Neurotoxicity (e.g., ataxia in dogs) at high doses or prolonged use
- Elevated liver enzymes
- Tachypnea, dyspnea, edema, and tachycardia (reported in dogs)
Precautions
Use cautiously in patients with documented hypersensitivity to other beta-lactam antibiotics (e.g., cephalosporins, cefamycins, carbapenems) due to potential cross-reactivity. Patients with severe renal dysfunction may require increased intervals between doses. Safe use during pregnancy has not been firmly established (FDA Category B; Papich Class A), use only when potential benefits outweigh risks.
Drug interactions
In vitro inactivation if mixed together; synergistic in vivo, but penicillins can inactivate aminoglycosides in patients with renal failure or when used in massive dosages. Amikacin is the most resistant to this inactivation.
Potential in vitro antagonism between beta-lactam antibiotics and bacteriostatic antibiotics; clinical importance is unclear.
Reduces the renal tubular secretion of both ampicillin and sulbactam, maintaining higher systemic levels for a longer period.
Monitoring
- Clinical efficacy (resolution of infection signs)
- Adverse effects (signs of hypersensitivity, neurological symptoms at high doses)
Pharmacokinetics
Absorption
Sulbactam sodium is not appreciably absorbed from the GI tract; must be given parenterally. When administered IV/IM, sulbactam's pharmacokinetic profile closely mirrors that of ampicillin in most species.
Distribution
Penicillins cross the placenta. Both ampicillin and sulbactam are distributed into breast milk in low concentrations.
Metabolism
Ampicillin undergoes minimal hepatic metabolism.
Elimination
Primarily excreted unchanged in the urine via glomerular filtration and active tubular secretion. In calves, plasma concentrations of sulbactam were consistently higher than ampicillin during the elimination phase.
Overdose
Neurological effects (e.g., ataxia) have rarely been reported in dogs receiving very high dosages of penicillins. In humans, very high dosages of parenteral penicillins, especially in those with renal disease, have induced CNS effects. If neurological signs develop, weigh the risks of continued use versus dosage reduction or switching to a different antibiotic class.
Available products
Formulations
- Powder for injection (reconstitution required)
Human-labeled
- Ampicillin Sodium/Sulbactam Sodium Powder (injection): 1.5 g (1 g ampicillin/0.5 g sulbactam)
- Ampicillin Sodium/Sulbactam Sodium Powder (injection): 3 g (2 g ampicillin/1 g sulbactam)
- Ampicillin Sodium/Sulbactam Sodium Powder (injection): 15 g bulk (10 g ampicillin/5 g sulbactam)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Unreconstituted powder should be stored at or below 30°C. Reconstituted to 45 mg/mL: stable for 8 hours at room temperature and 48 hours at 4°C. Reconstituted to 30 mg/mL: stable for 72 hours at 4°C. Diluted solutions in 0.9% NaCl for IV administration are stable at room temperature for 8 hours. IM reconstituted solutions should be administered within 1 hour.
Client information
- Hospital Use Only: Because this medication must be given by injection (IV or IM) and requires frequent dosing (every 6 to 8 hours), it is best administered to hospitalized patients.
- Purpose: It is a potent antibiotic combination used to treat severe or resistant bacterial infections, often utilized when oral medications cannot be tolerated.
- Safety: Generally very safe, but let your veterinary team know if your pet has ever had an allergic reaction to penicillin-type drugs.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.