Ampicillin
Ampicillin is a penicillin-type antibiotic used to treat a wide range of bacterial infections, including respiratory tract infections, urinary tract infections, meningitis, and gastrointestinal infections. It works by killing bacteria or preventing their growth, making it effective against both gram-positive and some gram-negative organisms.
Ampicillin is a broad-spectrum penicillin antibiotic used to treat various bacterial infections by inhibiting bacterial cell wall synthesis.
Key facts at a glance
- ATC
- J01CA01
- RxNorm
- 733
- Generic
- Ampicillin
- Class
- atc-j01
- Brands
- Polyflex, Unasyn
- Availability
- rx
- Lactation
- unknown
- Routes
- oral
- Forms
- solution, injection, capsule, suspension
- Regions
- US, EU, CN, JP
- Monitoring
- —
This page is for informational purposes only.
Do not use this information to diagnose yourself or to replace a physician's advice. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you believe you are experiencing a medical emergency, call your local emergency number immediately.
Dosage and administration
- Usual dose
- 500mg twice daily
- Maximum
- consult physician
- Frequency
- every 12 hours
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 250mg twice daily
- Maximum
- consult physician
- Frequency
- every 12 hours
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 400mg daily
- Maximum
- consult physician
- Frequency
- once daily
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
Overdose information
Special Populations
10 groupspregnancy
first trimesterno adjustment typically needed
use only if benefits outweigh risks, generally considered safe but avoid unnecessary use
regular prenatal monitoring
Use with caution and monitor for adverse effects.
pregnancy
second trimesterno adjustment typically needed
use when benefits outweigh risks
regular prenatal monitoring
Use with caution and monitor for adverse effects.
pregnancy
third trimesterno adjustment typically needed
use when benefits outweigh risks
regular prenatal monitoring
Use with caution and monitor for adverse effects.
lactation
breastfeedingno adjustment needed
compatible with breastfeeding, excreted in small amounts in breast milk
monitor infant for gastrointestinal disturbances
pediatric_age
neonatesweight-based dosing, reduced in premature infants
use with caution in neonates, especially premature, monitor for kernicterus
monitor bilirubin levels and renal function
Use with caution and monitor for adverse effects.
pediatric_age
childrenweight-based dosing 25-50mg/kg/day in divided doses
commonly used in children for susceptible infections
standard monitoring
geriatric
elderlyadjust based on renal function
monitor renal function, dose adjustment may be needed
monitor renal function and adjust dose accordingly
Use with caution and monitor for adverse effects.
renal_impairment
mildno adjustment needed for CrCl >30ml/min
use standard dosing, monitor renal function
periodic renal function monitoring
Use with caution and monitor for adverse effects.
renal_impairment
severereduce dose to 50% or extend interval
adjust dose based on CrCl, reduce to 250-500mg every 12 hours for CrCl <10ml/min
frequent renal function monitoring, serum drug levels if available
Use with caution and monitor for adverse effects.
hepatic_impairment
moderate to severeno major adjustment needed
use with caution, limited data available
monitor liver function tests
Use with caution and monitor for adverse effects.
Statistics and clinical data
FDA Approval Year
Original FDA approval date for Ampicillin
Drug class
Antibiotic class information
Common uses
Common therapeutic uses
Mechanism of action
Pharmacological mechanism
Ampicillin is used to treat respiratory tract infections (such as pneumonia and bronchitis), urinary tract infections, meningitis, gastrointestinal infections (including Salmonella), and certain skin and soft tissue infections. It may also be used for bacterial endocarditis prevention in some cases.
Ampicillin works by interfering with the bacteria's ability to form cell walls, which are essential for their survival. By inhibiting cell wall synthesis, the medication causes the bacteria to rupture and die, effectively eliminating the infection.
Ampicillin should not be used by individuals with penicillin allergies due to risk of severe allergic reactions. Common side effects include diarrhea, rash, and nausea. Resistance to ampicillin is increasingly common, so susceptibility testing may be needed. It is generally considered safe during pregnancy when clinically indicated.
Contraindications
Conditions and patient states where this medication should be avoided or used with caution.
Do not use (1)
Known allergy to this medication or its components
Use caution (1)
Consult healthcare provider for benefits vs risks assessment
Official drug label
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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 24, 2026. · Read our editorial policy