Drug reference

Ampicillin

Penicillin · Antibiotic

PenicillinAntibioticATC null

CDSCO approvedSchedule H

EXCRETION

—

not curated

INTERACTIONS

8 major

SEVERE in our sources

PREGNANCY

Not known to be harmful

FDA category + note

Top interactionssee all 12 →

DesogestrelSevereTextbook-citedKDT 7e · p948
EthinylestradiolSevereTextbook-citedKDT 7e · p948
LevonorgestrelSevereTextbook-citedKDT 7e · p948
NorethisteroneSevereTextbook-citedKDT 7e · p948

Mechanism

Ampicillin, a beta-lactam antibiotic, inhibits bacterial cell wall synthesis by irreversibly binding to penicillin-binding proteins (PBPs), which are transpeptidases essential for peptidoglycan cross-linking. This action prevents the formation of a stable cell wall, compromising bacterial structural integrity. The clinical consequence is bactericidal activity, leading to bacterial lysis and death.

Indications

Respiratory tract infections (sinusitis, otitis media, acute exacerbations of chronic bronchitis, epiglottitis, pneumonia)Enterococcus faecalis infectionsListeria infections (meningitis)Urinary tract infectionsEnterococcal bloodstream infectionsEnterococcal endocarditisWound infections (Pasteurella multocida)Prophylaxis for gonorrhoea/syphilisProphylaxis for catheterization (in patients with cardiac valvular lesions)Prevention of acute exacerbations in chronic obstructive lung disease (doubtful value)Prevention of acute exacerbations in chronic bronchitis (doubtful value)Surgical prophylaxisPPNG gonorrhoea (in combination with sulbactam)Mixed aerobic-anaerobic infections (intra-abdominal, gynaecological, surgical and skin/soft tissue infections), especially hospital-acquired (in combination with sulbactam)nonpenicillinase producing gonorrhoeaMild leptospirosis

Dosing

Adult: Oral: 0.5-1 g every 6 hours. IV/IM: 500 mg every 4-6 hours; up to 2 g every 4 hours for severe infections (endocarditis, meningitis).
Pediatric: 1-11 months: 125 mg QDS. 1-4 years: 250 mg QDS. 5-11 years: 500 mg QDS (max 1 g/dose). 12-17 years: 500 mg-1 g QDS.
Renal adjustment: Reduce dose if eGFR <10 mL/min/1.73m²
Max dose: 2 g every 4 hours IV (severe infections)

Pharmacokinetics

Half-life

Ampicillin has a relatively short half-life, but this is therapeutically acceptable in many cases.

Bioavailability

Food interferes with absorption

Excretion

Ampicillin attains high concentrations in bile.

Contraindications

Penicillin hypersensitivity

Side effects

Common

NauseaVomitingDiarrhoeaRash (especially with EBV/CLL)Superinfection risk (especially diarrhoea)Pseudomembranous enterocolitisPain at site of injection (with sulbactam)Thrombophlebitis of injected vein (with sulbactam)Rash (with sulbactam)Diarrhoea (with sulbactam)Gastrointestinal side effects (e.g., diarrhea)

Serious

Anaphylaxis
Clostridioides difficile colitis
Interstitial nephritis
Haemolytic anaemia
Hypersensitivity reactions (rash to anaphylaxis)
Serum sickness
Stevens-Johnson syndrome
Nephropathy
Hematologic reactions (neutropenia, prolonged use)
Neurotoxicity (seizure, high doses, renal impairment)

Pregnancy & lactation

Pregnancy

Not known to be harmful

Drug interactions

Desogestrel

Severe

Textbook-cited

Reduced contraceptive efficacy; risk of unintended pregnancy

Advise use of alternative or additional contraception during antibiotic course

Source: KDT 7e · p948

Ethinylestradiol

Severe

Textbook-cited

Reduced contraceptive efficacy; risk of unintended pregnancy

Advise use of alternative or additional contraception during antibiotic course

Source: KDT 7e · p948

Levonorgestrel

Severe

Textbook-cited

Reduced contraceptive efficacy; risk of unintended pregnancy

Advise use of alternative or additional contraception during antibiotic course

Source: KDT 7e · p948

Norethisterone

Severe

Textbook-cited

Reduced contraceptive efficacy; risk of unintended pregnancy

Advise use of alternative or additional contraception during antibiotic course

Source: KDT 7e · p948

Warfarin

Severe

Textbook-cited

Elevated INR and increased bleeding risk.

Monitor INR closely; reduce anticoagulant dose if needed

Source: KDT 7e · p948

Cloxacillin

Severe

Textbook

Reduced efficacy, increased bacterial resistance, higher cost, and more adverse effects. Ineffective against MRSA.

Blind therapy with this fixed-dose combination is irrational and harmful and should be avoided.

Source: KDT 7e · p723

Hydrocortisone

Severe

Textbook

Loss of ampicillin's antibacterial activity.

Do not mix hydrocortisone and ampicillin in the same IV solution.

Source: KDT 7e · p723

Methotrexate

Severe

Database

Increased risk of methotrexate toxicity (e.g., myelosuppression, mucositis, nephrotoxicity).

Monitor methotrexate levels and for signs of toxicity. Consider a dose reduction of methotrexate or an alternative antibiotic if co-administration is necessary. Ensure adequate hydration.

Source: DDInter

Allopurinol

Moderate

Textbook-cited

Significantly increased incidence of skin rashes.

Avoid concurrent use where possible

Source: KDT 7e · p948

Azithromycin

Moderate

Textbook-cited

Reduced antibacterial efficacy; therapeutic failure.

Avoid concurrent use of bacteriostatic and bactericidal antibiotics