Antibiotic Class

Penicillin (aminopenicillin)

Antimicrobial Spectrum

Gram-positive:  Streptococcus spp., Enterococcus spp., Listeria monocytogenes

Gram-negative:  H. influenzae, E. coli, Proteus mirabilis, Salmonella spp., Shigella spp.

Mechanism of Action

Exerts bactericidal activity via inhibition of bacterial cell wall synthesis by binding one or more of the penicillin binding proteins (PBPs). Exerts bacterial autolytic effect by inhibition of certain PBPs related to the activation of a bacterial autolytic process.


Penicillins produce time-dependent killing


Cmax: 40mcg/ml; Half-life: 1-1.3h; Table 6 

Adverse Effects

Hematologic:  anemia, thrombocytopenia, neutropenia, agranulocytosis

CNS:  seizures

Renal:  nephrotoxicity, interstitial nephritis

Hepatic:  transient increases in transaminases

Other:  Jarisch-Herxheimer Reaction (fever, chills, sweating, tachycardia, hyperventilation, flushing, and myalgia)


Adult:  250-500mg po q6h

1-2g IV q4h

Pediatric:   1 month and < 40 kg: 50-200 mg/kg day IV in 4-6 divided doses

< 1 week: 25 mg/kg IV/IM q 8-12h

1 week and < 1 month: 25 mg/kg IV/IM q6-8h

> 40 kg: usual adult dose

Disease state based dosing

Renal failure:  CrCL 10-50 mL/min: Extend dosing interval to q 6-12h

                     CrCL < 10 mL/min: Extend dosing interval to q8-16h



hypersensitivity to ampicillin or other penicillins


Drug Interactions

Allopurinol higher probablility of ampicillin rash; Atenolol decreased atenolol effectiveness; Contraceptives - decreased contraceptive effectiveness; Lansoprazole loss of ampicillin efficacy; Live Typhoid Vaccine - decreased immunological response to the typhoid vaccine; Omeprazole loss of ampicillin efficacy; Pantoprazole loss of ampicillin efficacy; Probenecid - increased ampicillin levels; Rabeprazole loss of ampicillin efficacy


Category B:No evidence of risk in humans but studies inadequate.

Monitoring Requirements

Therapeutic:  Culture and sensitivities, signs and symptoms of infection

Toxic:  Periodic CBC, urinalysis, BUN, Creatinine, AST and ALT, diarrhea, skin rash

Brand names/Manufacturer

Available by many names and manufacturers (click here)