Ampicillin: Broad-Spectrum Antibiotic for Bacterial Infection Control
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Synonyms | |||
Ampicillin is a broad-spectrum aminopenicillin antibiotic derived from the penicillin nucleus, specifically designed to combat a wide range of 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 clinical settings due to its activity against both aerobic and anaerobic organisms, making it a first-line option for numerous common and serious infections. Available in oral and parenteral formulations, it combines efficacy with a well-established safety profile when used appropriately under medical supervision.
Features
- Semi-synthetic beta-lactam antibiotic from the aminopenicillin class
- Available as capsules (250 mg, 500 mg), oral suspension (125 mg/5 mL, 250 mg/5 mL), and injectable formulations
- Broad-spectrum activity covering Streptococcus spp., Listeria, Enterococcus, Haemophilus influenzae, E. coli, Proteus mirabilis, and Salmonella
- Stable in gastric acid, allowing for effective oral absorption
- Excreted largely unchanged in urine, with a serum half-life of approximately 1 hour in adults with normal renal function
Benefits
- Effectively treats respiratory, urinary, gastrointestinal, and meningeal infections
- Provides reliable coverage for mixed aerobic-anaerobic infections
- Suitable for use in both adult and pediatric populations
- Lower risk of Clostridium difficile-associated diarrhea compared to broader-spectrum alternatives
- Cost-effective option for empiric and directed therapy in many clinical scenarios
- May be used prophylactically in certain surgical procedures
Common use
Ampicillin is commonly prescribed for bacterial infections caused by susceptible organisms, including respiratory tract infections such as bronchitis and pneumonia, urinary tract infections, otitis media, sinusitis, and gastrointestinal infections including salmonellosis and shigellosis. It is also utilized in the treatment of bacterial meningitis, endocarditis prophylaxis in high-risk patients, and intra-abdominal infections when combined with a beta-lactamase inhibitor. In obstetric practice, it is frequently employed for Group B Streptococcus prophylaxis during delivery.
Dosage and direction
Dosage varies significantly based on infection severity, patient age, renal function, and route of administration. For mild to moderate infections in adults, the typical oral dosage is 250-500 mg every 6 hours. For severe infections, intravenous administration of 1-2 g every 4-6 hours is common. Pediatric dosing is typically 50-100 mg/kg/day divided every 6 hours for oral administration, and 100-200 mg/kg/day divided every 4-6 hours for IV administration, not to exceed adult doses. All dosage regimens should be adjusted in renal impairment. Treatment should continue for at least 48-72 hours after symptoms resolve and cultures become negative, typically ranging from 7-14 days depending on infection type.
Precautions
Patients should complete the entire prescribed course even if symptoms improve to prevent resistance development. Use with caution in patients with mononucleosis due to high risk of rash. Monitor renal, hepatic, and hematopoietic function during prolonged therapy. May result in overgrowth of nonsusceptible organisms including fungi. Use during pregnancy only if clearly needed (Category B). Ampicillin is excreted in breast milk and may cause sensitization, diarrhea, or candidiasis in nursing infants. False-positive urinary glucose tests may occur with copper reduction methods.
Contraindications
Ampicillin is contraindicated in patients with known hypersensitivity to penicillins, other beta-lactam antibiotics, or any component of the formulation. History of amoxicillin/clavulanate-associated cholestatic jaundice or hepatic dysfunction constitutes a relative contraindication. Should not be administered to patients with previous ampicillin-associated antibiotic-associated colitis.
Possible side effect
Common adverse reactions include diarrhea (6%), nausea (4%), vomiting (2%), rash (5-10%), and urticaria. Less frequently observed effects include glossitis, stomatitis, black hairy tongue, enterocolitis, pseudomembranous colitis, hemolytic anemia, thrombocytopenia, eosinophilia, leukopenia, agranulocytosis, transient elevations in liver enzymes, and interstitial nephritis. Hypersensitivity reactions ranging from skin rashes to anaphylaxis may occur, particularly in patients with history of allergy, asthma, or hay fever.
Drug interaction
Probenecid decreases renal tubular secretion of ampicillin, increasing and prolonging serum levels. Concurrent use with allopurinol may increase incidence of skin rashes. Ampicillin may reduce the efficacy of oral contraceptives; additional contraceptive methods are recommended. May potentiate anticoagulant effect of warfarin through reduction of vitamin K-producing gut flora. Bacteriostatic antibiotics (tetracyclines, erythromycin) may interfere with bactericidal activity. False-positive urinary glucose tests may occur with Benedict’s solution, Fehling’s solution, or Clinitest tablets.
Missed dose
If a dose is missed, it should be taken as soon as remembered unless it is almost time for the next scheduled dose. In that case, skip the missed dose and resume the regular dosing schedule. Do not double the dose to make up for a missed one. Maintaining consistent antibiotic levels is important for efficacy, so patients should strive for regular dosing intervals.
Overdose
Ampicillin overdose may manifest as neuromuscular hypersensitivity or convulsions, particularly in patients with renal impairment. Gastrointestinal effects including nausea, vomiting, and diarrhea are common. Management is primarily supportive, with maintenance of hydration and electrolyte balance. Hemodialysis can remove approximately 15-25% of the circulating ampicillin and may be considered in severe cases, particularly with renal impairment.
Storage
Store capsules and powder for oral suspension at controlled room temperature (20-25°C or 68-77°F). Keep container tightly closed and protect from moisture. Reconstituted oral suspension is stable for 14 days at room temperature or under refrigeration; discard any unused portion after this period. Parenteral solutions should be stored according to manufacturer instructions and used within specified stability periods after reconstitution.
Disclaimer
This information is for educational purposes only and does not constitute medical advice. Ampicillin is a prescription medication that should be used only under the supervision of a qualified healthcare provider. Dosage and treatment duration must be individualized based on specific infection, patient factors, and local resistance patterns. Always consult with a healthcare professional for diagnosis and appropriate treatment recommendations.
Reviews
Clinical studies consistently demonstrate ampicillin’s efficacy in treating susceptible infections, with success rates of 85-95% for indicated uses. Healthcare providers appreciate its predictable spectrum and cost-effectiveness, though note increasing resistance in some regions. Patients generally tolerate it well, with gastrointestinal complaints being the most frequently reported issue. The drug remains a valuable tool in antimicrobial therapy nearly six decades after its introduction, particularly in settings where resistance patterns remain favorable.