Penicillin   (PDF Version)


Antibiotic Class:

Penicillin (natural penicillin)


Antimicrobial Spectrum:

Gram-positive:  non-beta-lactamase producing gram-positive cocci (including viridans streptococci, group A streptococci, Streptococcus pneumoniae, anaerobic Streptococcus), Enterococcus spp., non-penicillinase producing strains of Staphylococcus aureus, coagulase negative Staphylococcus aureus, Clostridium spp. (excluding C. difficile), Actinomyces spp.


Gram negative:  Neisseria meningitides, non-penicillinase producing Neisseria gonorrheae, Pasteurella multocida


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



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)



Table 7


Disease state based dosing:

Renal failure:  Table 7



Contraindications:  hypersensitivity to ampicillin or other penicillins



Drug Interactions:

Chloramphenicol - decreased antibacterial effectiveness

Cholestyramine - decreased penicillin absorption

Contraceptives - decreased contraceptive effectiveness

Live Typhoid Vaccine - decreased immunological response to the typhoid vaccine

Probenecid - increased penicillin levels



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, SCr, AST and ALT, diarrhea, skin rash


Brand names/Manufacturer:

Available by many names and manufacturers (click here)