Ampicillin is an antibiotic in the beta-lactam family of antibiotics. It is a Penicillin derivative.

  • Type: Penicillin
  • Dosage Forms: capsule, oral suspension, powder for injection
  • Dosage Strengths: capsule: 250, 500mg; oral suspension: 125, 250mg/5mL; powder for injection: 125mg, 250mg, 500mg, 1g, 2g, 10g
  • Routes of Administration: PO, IV, IM
  • Common Trade Names: Ampi, Omnipen, Penglobe, Principen

Adult Dosing


  • 12 g daily (continuous IV infusion or in 6 equally divided dosages) in conjunction with gentamicin

Perinatal Group B Streptococcal Prevention

  • Initial 2 g dose at time of labor or rupture of membranes, followed by 1 g q4hrs until delivery

Pediatric Dosing

Pneumonia (peds)

  • 150-200mg/kg/day IV divided Q6hours (max dose: 4g per day)

Other Pediatric Bacterial Infections

  • 100-400mg/kg/day IM/IV divided q4-16Hours (max dose 12g/day IM/IV)

Special Populations

  • Pregnancy Rating: B
  • Lactation: Excreted in breastmilk, use caution
  • Renal dosing:
    • CrCl <10 mL/min: Administer q12-24hr
    • CrCl 10-50 mL/min: Administer q6-12hr
    • CrCl >50 mL/min: Administer q6hr
  • Hepatic Dosing: not studied


  • Allergy to class/drug

Adverse Reactions


  • Pseudomembranous colitis, enterocolitis
  • Agranulocytosis
  • Seizure
  • Interstitial nephritis
  • Stridor
  • Anaphylaxis


  • Rash, urticaria
  • Diarrhea, nausea
  • Fever
  • Oral candidiasis
  • Stomatitis, glossitis
  • Anemia/hemolytic anemia, leukopenia, thrombocytopenia, eosinophilia
  • Serum sickness like reaction
  • Elevated AST
  • Erythema multiforme


  • Half-life: 1-1.8 hr (normal renal function); 7-20 hr (anuria/ESRD)
  • Metabolism: Hepatic
  • Excretion: Urine
  • Mechanism of Action: Bactericidal; inhibits bacterial cell wall synthesis

Antibiotic Sensitivities[1]

Group Organism Sensitivity
Gram Positive Strep. Group A, B, C, G S
Strep. Pneumoniae S
Viridans strep I
Strep. anginosus gp S
Enterococcus faecalis S
Enterococcus faecium I
Staph. Epidermidis R
C. jeikeium R
L. monocytogenes S
Gram Negatives N. gonorrhoeae R
N. meningitidis S
Moraxella catarrhalis R
H. influenzae I
E. coli I
Klebsiella sp R
E. coli/Klebsiella ESBL+ R
E coli/Klebsiella KPC+ R
Enterobacter sp, AmpC neg R
Enterobacter sp, AmpC pos R
Serratia sp R
Serratia marcescens X1
Salmonella sp I
Shigella sp I
Proteus mirabilis S
Proteus vulgaris R
Providencia sp. R
Morganella sp. R
Citrobacter freundii R
Citrobacter diversus R
Citrobacter sp. R
Aeromonas sp R
Acinetobacter sp. R
Pseudomonas aeruginosa R
Burkholderia cepacia R
Stenotrophomonas maltophilia R
Yersinia enterocolitica R
Francisella tularensis X1
Brucella sp. X1
Legionella sp. R
Pasteurella multocida S
Haemophilus ducreyi R
Vibrio vulnificus X1
Misc Chlamydophila sp R
Mycoplasm pneumoniae R
Rickettsia sp X1
Mycobacterium avium X1
Anaerobes Actinomyces S
Bacteroides fragilis R
Prevotella melaninogenica S
Clostridium difficile X1
Clostridium (not difficile) S
Fusobacterium necrophorum S
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. Sanford Guide to Antimicrobial Therapy 2014