Ampicillin
PRINCIPEN
Pronunciation: am-pi-SIL-in
“Prince Amp-a-ceiling”
beta lactam ring
What it isAminopenicillin; Listeria, enterococcal and susceptible Gram-negative infection.
Why this oneThe drug for Listeria meningitis, which cephalosporins do not cover.
What limits itBeta-lactamase producers escape it. Rash with concurrent EBV; frequent dosing.
Ampicillin prescription history
Animated chart of estimated U.S. prescriptions per year, Penicillins (oral) (1955–2026). Ampicillin enters in 1963.
FDA-approved for
- bacterial infections (1963)
- Listeria/Enterococcus infections (1963)
Principal riskHypersensitivity; beta-lactamase producers escape it
Classes and tags
Clinical profile
Legacy pregnancy categoryB
Defining liabilityAllergy, gastrointestinal effects and agent-specific renal, hepatic, hematologic or interaction risks.
FDA label
Read the full label on DailyMed ↗
NO BOXED WARNINGS
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Genitourinary/GI tract infections | Adults & children >20 kg | 500 mg QID | ||
| Respiratory tract infections | Adults & children >20 kg | 250 mg QID | ||
| Gonorrhea | Adult | Single 3.5 g dose with 1 g probenecid | ||
| Genitourinary/GI tract infections | Children <=20 kg | 100 mg/kg/day divided QID | ||
| Respiratory tract infections | Children <=20 kg | 50 mg/kg/day divided TID-QID |
Renal Undefined
Hepatic Undefined
Instructions
- Administer at least 30 min before or 2 h after meals for maximal absorption
- Doses for children should not exceed doses recommended for adults
Available strengths
- cap 250, 500 mg
Contraindications
- Serious hypersensitivity (e.g., anaphylaxis, Stevens-Johnson syndrome) to ampicillin or other beta-lactams
- Infections caused by penicillinase-producing organisms
- Previous history of cholestatic jaundice/hepatic dysfunction associated with ampicillin
Cautions
- Hypersensitivity/anaphylactic reactions (more likely with prior penicillin allergy)
- Clostridioides difficile-associated diarrhea
Adverse reactions
- Hypersensitivity reactions (rash, urticaria)
- Diarrhea (incl. C. difficile-associated)
- Nausea, vomiting
- Glossitis, stomatitis
Pregnancy Animal reproduction studies revealed no evidence of impaired fertility or fetal harm; no adequate and well-controlled studies in pregnant women.
Lactation Undefined
Cost
| Strength | #/mo | generic $/mo | CostPlus | |
|---|---|---|---|---|
| 250 mg | cap | 120 QID | not offered | |
| 500 mg | cap | 120 QID | $52.93 | offered |
Available combined with: ampicillin / sulbactam
Generic entry1985
Open Ampicillin in the interactive console ↗
Self-check
- Which meningitis pathogen does ampicillin cover but cephalosporins do not?
Listeria. - What bacterial defense defeats ampicillin?
Beta-lactamase production.