Ampicillin is a broad-spectrum aminopenicillin antibiotic derived from the penicillin class, designed to combat a wide range of gram-positive and gram-negative bacterial infections. Its bactericidal action inhibits bacterial cell wall synthesis, making it a first-line treatment for respiratory, urinary, gastrointestinal, and meningeal infections. Trusted by healthcare professionals for decades, ampicillin combines efficacy with a well-understood safety profile when used appropriately under medical supervision.

Features

• Broad-spectrum activity against susceptible gram-positive and gram-negative bacteria
• Available in oral (capsules, suspension) and parenteral (IV, IM) formulations
• Acid-stable for reliable oral absorption
• Bactericidal mechanism via inhibition of transpeptidase enzymes in cell wall synthesis
• Typically dosed 2–4 times daily based on infection severity and patient factors

Benefits

• Effectively treats common and serious bacterial infections, reducing complication risks
• Suitable for both community-acquired and some hospital-acquired infections
• May be used in certain pediatric populations under careful dosing guidance
• Lower cost compared to many newer broad-spectrum antibiotics
• Rapid onset of action when administered intravenously in severe cases
• Can be part of combination therapy for enhanced spectrum coverage

Common use

Ampicillin is commonly prescribed for infections caused by susceptible organisms, including streptococci, enterococci, Listeria monocytogenes, Haemophilus influenzae, Escherichia coli, Proteus mirabilis, and Salmonella species. Typical indications include respiratory tract infections (such as bronchitis and pneumonia), urinary tract infections, bacterial meningitis, gastrointestinal infections (including Salmonella typhi), endocarditis prophylaxis in high-risk patients, and septicemia. It is also used in obstetric and gynecological infections and intra-abdominal infections when combined with beta-lactamase inhibitors.

Dosage and direction

Dosage varies significantly based on infection type, severity, patient age, renal function, and route of administration. Adults typically receive 250–500 mg orally every 6 hours, or 1–2 g IV/IM every 4–6 hours for severe infections. For meningitis, doses up to 12 g/day IV in divided doses may be used. Pediatric dosing is weight-based, generally 50–100 mg/kg/day in divided doses every 6–8 hours, not exceeding adult doses. Oral administration should occur on an empty stomach (1 hour before or 2 hours after meals) for optimal absorption, unless gastrointestinal upset occurs. Treatment duration typically ranges from 5–14 days depending on infection resolution. Always complete the full prescribed course even if symptoms improve earlier.

Precautions

Use with caution in patients with history of hypersensitivity reactions to other beta-lactam antibiotics. Monitor renal, hepatic, and hematopoietic function during prolonged therapy. May cause antibiotic-associated colitis; discontinue if diarrhea develops. Use cautiously in patients with mononucleosis due to increased rash risk. Superinfections with fungi or resistant bacteria may occur. In pregnancy, use only if clearly needed (Category B). Ampicillin excretes in breast milk; consider temporary discontinuation of nursing. False-positive urinary glucose tests may occur with copper reduction methods.

Contraindications

Hypersensitivity to ampicillin, other penicillins, or any component of the formulation. History of ampicillin-associated cholestatic jaundice/hepatic dysfunction. Concomitant use with bacteriostatic antibiotics may reduce efficacy. Not recommended for treatment of viral infections or prophylactic use without specific indication. Avoid in patients with previous penicillin-associated hemolytic anemia.

Possible side effect

Common: diarrhea, nausea, vomiting, rash, urticaria. Less common: pseudomembranous colitis, glossitis, stomatitis, black “hairy” tongue, vaginal candidiasis, eosinophilia. Rare but serious: anaphylaxis, Stevens-Johnson syndrome, toxic epidermal necrolysis, hepatitis, cholestatic jaundice, leukopenia, neutropenia, thrombocytopenia, anemia, interstitial nephritis, seizures (with high doses in renal impairment). Report any severe rash, difficulty breathing, or persistent diarrhea to healthcare provider immediately.

Drug interaction

Probenecid decreases renal excretion, increasing ampicillin levels. Allopurinol may increase incidence of skin rashes. Ampicillin may reduce efficacy of oral contraceptives; recommend alternative contraception during therapy. May potentiate anticoagulant effect of warfarin; monitor INR closely. Concurrent use with bacteriostatic antibiotics (e.g., tetracyclines, chloramphenicol) may diminish bactericidal effect. Live bacterial vaccines (typhoid) may have reduced efficacy; avoid concurrent administration.

Missed dose

Take the missed dose as soon as remembered, unless it is almost time for the next scheduled dose. Do not double the dose to make up for a missed one. Maintain regular dosing intervals to ensure consistent therapeutic blood levels. If multiple doses are missed, contact healthcare provider for guidance on resuming therapy.

Overdose

Symptoms may include nausea, vomiting, diarrhea, electrolyte imbalances, and neuromuscular hypersensitivity. Seizures may occur with massive overdoses, particularly in patients with renal impairment. Management is supportive; maintain hydration and electrolyte balance. Hemodialysis may enhance elimination in cases of significant overdose, removing approximately 30–40% of the drug in 4–6 hours. There is no specific antidote.

Storage

Store at controlled room temperature (20–25°C/68–77°F). Keep oral suspension refrigerated after reconstitution; discard after 14 days. Protect from moisture and light. Keep all medications out of reach of children and pets. Do not use after expiration date. Do not freeze. IV solutions should be used within specified stability periods (typically 1–8 hours at room temperature depending on concentration and diluent).

Disclaimer

This information is for educational purposes only and does not constitute medical advice. Ampicillin is a prescription medication that should only be used under the supervision of a qualified healthcare professional. Dosage and treatment duration must be individualized based on specific infection, patient factors, and local resistance patterns. Always consult with a healthcare provider for diagnosis and appropriate treatment recommendations. Self-medication with antibiotics contributes to antimicrobial resistance.

Reviews

“Ampicillin remains a workhorse antibiotic in our infectious disease department, particularly for susceptible enterococcal infections and Listeria meningitis. Its predictable pharmacokinetics and cost-effectiveness make it valuable in both inpatient and outpatient settings.” — Infectious Disease Specialist, 15 years experience

“I’ve prescribed ampicillin for decades for appropriate UTIs and respiratory infections. When susceptibility is confirmed, it provides reliable coverage without the expense of broader-spectrum agents. The main challenge is increasing resistance patterns in some communities.” — General Practitioner, 28 years experience

“As a clinical pharmacist, I appreciate ampicillin’s well-characterized safety profile and flexibility in dosing. The need for multiple daily doses can affect adherence, but for serious infections, IV administration provides excellent tissue penetration.” — Hospital Pharmacist, 10 years experience

“My child was successfully treated with ampicillin for a confirmed streptococcal infection. The liquid formulation was tolerable, and we completed the full course without issues. I appreciate that it’s a older antibiotic with extensive safety data in children.” — Parent of pediatric patient