Ampicillin is a broad-spectrum aminopenicillin antibiotic derived from the penicillin class, widely prescribed for its efficacy against both gram-positive and gram-negative bacteria. It functions by inhibiting bacterial cell wall synthesis, leading to osmotic instability and cell lysis. This bactericidal agent is particularly valuable in treating a diverse range of infections, including respiratory, urinary, gastrointestinal, and meningeal infections, making it a cornerstone in empirical and targeted antimicrobial therapy.

Features

• Broad-spectrum activity against gram-positive and gram-negative organisms
• Beta-lactam structure with enhanced stability in acidic environments compared to earlier penicillins
• Available in oral (capsules, suspension) and parenteral (IV, IM) formulations
• Well-established pharmacokinetic profile with good tissue penetration, including cerebrospinal fluid when meninges are inflamed

Benefits

• Rapid bactericidal action reduces bacterial load and hastens clinical improvement
• Effective against common pathogens such as Streptococcus pneumoniae, Haemophilus influenzae, Escherichia coli, and Proteus mirabilis
• Suitable for use in both community and hospital settings due to its versatile administration routes
• Lower incidence of serious adverse effects compared to some broader-spectrum alternatives when used appropriately
• Cost-effective option within the antibiotic armamentarium

Common use

Ampicillin is indicated for the treatment of infections caused by susceptible strains of microorganisms. Common clinical applications include respiratory tract infections such as bronchitis and pneumonia, urinary tract infections, bacterial meningitis (especially in pediatric populations), gastrointestinal infections including salmonellosis, and septicemia. It is also used prophylactically to prevent bacterial endocarditis in high-risk patients undergoing dental or surgical procedures.

Dosage and direction

Dosage varies based on infection severity, patient age, renal function, and route of administration. For mild to moderate infections in adults, the typical oral dose is 250–500 mg every 6 hours. For severe infections or parenteral administration, doses range from 1–2 g every 4–6 hours intravenously or intramuscularly. Pediatric dosing is weight-based, generally 50–100 mg/kg/day divided every 6–8 hours, not exceeding adult doses. Duration of therapy typically ranges from 7 to 14 days depending on infection type and clinical response. Always complete the full course as prescribed, even if symptoms improve earlier.

Precautions

Use with caution in patients with a history of hypersensitivity reactions to penicillins, cephalosporins, or other beta-lactam antibiotics due to cross-reactivity risk. Monitor renal and hepatic function during prolonged therapy. Superinfection with resistant organisms, including fungi, may occur. Ampicillin may reduce the efficacy of oral contraceptives; advise alternative contraception during treatment. In patients with mononucleosis, a high incidence of maculopapular rash has been observed.

Contraindications

Ampicillin is contraindicated in individuals with a known hypersensitivity to penicillins or other beta-lactam antibiotics. It should not be used in patients with a history of ampicillin-associated hepatitis or cholestatic jaundice. Avoid administration to patients with infectious mononucleosis due to the high likelihood of non-allergic rash.

Possible side effect

Common side effects include gastrointestinal disturbances such as nausea, vomiting, diarrhea, and glossitis. Hypersensitivity reactions range from maculopapular rash to urticaria, fever, and eosinophilia. Rare but serious adverse effects include Clostridium difficile-associated diarrhea, Stevens-Johnson syndrome, anaphylaxis, hematologic abnormalities (e.g., leukopenia, thrombocytopenia), and transient elevations in liver enzymes. Interstitial nephritis has been reported with prolonged use.

Drug interaction

Probenecid decreases renal tubular secretion of ampicillin, increasing and prolonging serum levels. Concurrent use with allopurinol may increase the incidence of skin rashes. Ampicillin may reduce the effectiveness of oral contraceptives. Bacteriostatic antibiotics like tetracyclines may antagonize ampicillin’s bactericidal effect. It may also potentiate the effects of warfarin, requiring closer monitoring of INR.

Missed dose

If a dose is missed, take it 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. Maintaining consistent serum levels is important for efficacy, so try to adhere to the prescribed dosing schedule.

Overdose

Symptoms of overdose may include nausea, vomiting, diarrhea, and electrolyte imbalances. Neurological manifestations such as convulsions may occur, especially in patients with renal impairment. Management is supportive; hemodialysis can enhance elimination of the drug. There is no specific antidote.

Storage

Store capsules and powder for oral suspension at room temperature (15–30°C), protected from light and moisture. Reconstituted oral suspension is stable for 14 days under refrigeration (2–8°C); do not freeze. Parenteral solutions should be used immediately after reconstitution; follow manufacturer guidelines for stability under refrigeration.

Disclaimer

This information is intended for medical professionals and should not replace personalized advice from a qualified healthcare provider. Always confirm susceptibility testing and dosing based on individual patient factors, local resistance patterns, and current clinical guidelines.

Reviews

Ampicillin remains a well-regarded antibiotic in clinical practice, particularly noted for its reliability in treating susceptible infections and its favorable safety profile. Clinicians appreciate its versatility across age groups and infection sites, though emerging resistance patterns necessitate ongoing susceptibility testing. It continues to be a first-line option in many guidelines for specific indications such as Listeria meningitis and enterococcal infections.