C. diff Risk


Oral Bioavailability


Approximate Cost


Usual dose
2g IV q4-6h

Meningitis OR Infective Endocarditis OR Osteomyelitis
2g IV q4h

General Information

Common Usage

Ampicillin is commonly used as pathogen directed therapy for intravascular, intra-abdominal and urinary infections secondary to certain Enterococcus spp.

Ampicillin is used as empiric therapy for bacterial meningitis if risk factors for Listeria monocytogenes are present.

Adverse Effects

Allergic reactions, rash
Clostridium difficile associated diarrhea

Major Interactions

Allopurinol - increased risk of rash

Additional Information

Patients with infectious mononucleosis secondary to EBV and given amoxicillin or ampicillin may develop a rash and this is not indicative of a true allergy.


Antimicrobial class: Aminopenicillin

Pregnancy category: B

Average serum half life: 1 hour

Biliary penetration: Therapeutic

CSF penetration: Therapeutic

Lung penetration: Therapeutic

Urine penetration: Therapeutic