• Type: Amino-Penicillins
  • Dosage Forms: powder for solution
  • Dosage Strengths: 1.5g, 3g, 15g
  • Routes of Administration: IM, IV
  • Common Trade Names: Unasyn

Adult Dosing


  • 1.5-3g IV/IM q6 hours
  • Max: 12g/day

Bite (for Pasteurella multocida Coverage)

  • 1.5-3g IM/IV q6 hours

Orbital Cellulitis

  • 3g IM/IV q6 hours

Diabetic Foot Osteomyelitis[1]

  • 3g IM/IV q6 hours



  • Aspiration or CAP
    • 1.5-3g IM/IV q6 hours
  • Hospital-acquired: 3g IM/IV q6 hours

UTI, Pyelonephritis

  • 3g IM/IV q6 hours x 14 days

Pediatric Dosing (<40kg)

Unasyn (ampicillin/sulbactam) is formulated at a 2:1 ratio (3g vial = 2g ampicillin + 1g sulbactam)


  • Mild-moderate
    • 100-200mg ampicillin/kg/day IM/IV divided q6 hours
    • First Dose: 25-50mg ampicillin/kg IM/IV x 1 (37.5-75mg Unasyn/kg IM/IV x 1)
    • Max: 1000mg ampicillin (1500mg Unasyn)
  • Severe
    • 200mg ampicillin/kg/day IM/IV divided q6 hours
    • First Dose: 50mg ampicillin/kg IM/IV x 1 (75mg Unasyn/kg IM/IV x 1)
    • Max: 2000mg ampicillin (3000mg Unasyn)


  • 400mg ampicillin/kg/day IM/IV divided q6 hours
  • First Dose: 100mg ampicillin/kg IM/IV x 1 (150mg Unasyn/kg IM/IV x 1)
  • Max: 2000mg ampicillin (3000mg Unasyn)


  • 200mg ampicillin/kg/day IM/IV divided q4-6 hours +/- gentamicin x 4-6 weeks


  • 200mg ampicillin/kg/day IM/IV divided q6 hours

Special Populations

  • Pregnancy: B
  • Lactation: Use caution
  • Renal Dosing
    • Adult
    • Pediatric
  • Hepatic Dosing
    • Adult
    • Pediatric


  • Allergy to class/drug

Adverse Reactions


  • Anaphylaxis


  • Headache
  • Itching
  • Nausea
  • Vomiting


  • Half-life: One hour
  • Metabolism:
  • Excretion: Renal (75% excreted in active form), Bile (very small amount)[3]
  • Mechanism of Action: Bactericidal (Binds to penicillin-binding proteins to block cell wall synthesis), coupled with β-lacatamase inhibitor

Antibiotic Sensitivities[4]

Group Organism Sensitivity
Gram PositiveStrep. Group A, B, C, GS
Strep. PneumoniaeS
Viridans strepI
Strep. anginosus gpS
Enterococcus faecalisS
Enterococcus faeciumS
Staph. EpidermidisR
C. jeikeiumR
L. monocytogenesS
Gram NegativesN. gonorrhoeaeS
N. meningitidisS
Moraxella catarrhalisS
H. influenzaeS
E. coliS
Klebsiella spS
E. coli/Klebsiella ESBL+R
E coli/Klebsiella KPC+R
Enterobacter sp, AmpC negR
Enterobacter sp, AmpC posR
Serratia spR
Serratia marcescensX1
Salmonella spS
Shigella spS
Proteus mirabilisS
Proteus vulgarisS
Providencia sp.S
Morganella sp.S
Citrobacter freundiiR
Citrobacter diversusR
Citrobacter sp.R
Aeromonas spS
Acinetobacter sp.S
Pseudomonas aeruginosaR
Burkholderia cepaciaR
Stenotrophomonas maltophiliaR
Yersinia enterocoliticaI
Francisella tularensisX1
Brucella sp.X1
Legionella sp.R
Pasteurella multocidaS
Haemophilus ducreyiS
Vibrio vulnificusX1
MiscChlamydophila spR
Mycoplasm pneumoniaeR
Rickettsia spX1
Mycobacterium aviumX1
Bacteroides fragilisS
Prevotella melaninogenicaS
Clostridium difficileX2
Clostridium (not difficile)S
Fusobacterium necrophorumS
Peptostreptococcus sp.S


  • S susceptible/sensitive (usually)
  • I intermediate (variably susceptible/resistant)
  • R resistant (or not effective clinically)
  • S+ synergistic with cell wall antibiotics
  • U sensitive for UTI only (non systemic infection)
  • X1 no data
  • X2 active in vitro, but not used clinically
  • X3 active in vitro, but not clinically effective for Group A strep pharyngitis or infections due to E. faecalis
  • X4 active in vitro, but not clinically effective for strep pneumonia

See Also


  1. Lipsky, 2004
  2. Red Book, 2012
  3. Campoli-Richards DM, Brogden RN. (1987). ". Sulbactam/ampicillin: a review of its antibacterial activity, pharmacokinetic properties, and therapeutic use". Drugs. 33 (6): 577–609. doi:10.2165/00003495-198733060-00003. PMID 3038500
  4. Sanford Guide to Antimicrobial Therapy 2014
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