Ampicillin: Broad-Spectrum Antibiotic for Effective Bacterial Infection Control
Ampicillin
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| Product dosage: 500mg | |||
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Synonyms | |||
Ampicillin is a broad-spectrum aminopenicillin antibiotic belonging to the beta-lactam class, widely utilized in clinical practice for its efficacy against a diverse range of gram-positive and gram-negative bacteria. It functions by inhibiting bacterial cell wall synthesis, leading to osmotic instability and eventual cell lysis. This bactericidal agent is particularly valuable in treating respiratory, urinary, gastrointestinal, and meningeal infections, and remains a cornerstone in empiric and targeted antimicrobial therapy. Its well-established pharmacokinetic profile and generally favorable safety record make it a first-line option in both inpatient and outpatient settings.
Features
- Chemical structure: Aminopenicillin, beta-lactam antibiotic
- Mechanism of action: Inhibition of bacterial cell wall synthesis via binding to penicillin-binding proteins (PBPs)
- Spectrum: Active against many gram-positive organisms (including Streptococcus species, Enterococcus faecalis) and gram-negative bacteria (such as Haemophilus influenzae, Escherichia coli, Proteus mirabilis, Salmonella, Shigella)
- Administration forms: Oral capsules (250 mg, 500 mg), powder for oral suspension (125 mg/5 mL, 250 mg/5 mL), intravenous and intramuscular formulations
- Bioavailability: Approximately 40% orally; significantly higher with parenteral administration
- Half-life: Approximately 1–1.5 hours in adults with normal renal function
- Excretion: Primarily renal (unchanged)
Benefits
- Provides broad-spectrum coverage against common pathogenic bacteria, reducing the need for combination therapy in many cases
- Bactericidal action ensures rapid reduction in bacterial load, promoting quicker symptomatic relief and recovery
- Well-tolerated profile with a lower incidence of severe adverse effects compared to many other antibiotic classes
- Suitable for use across diverse patient populations, including pediatric and geriatric cohorts, with appropriate dosing adjustments
- Cost-effective therapeutic option with widespread availability in both generic and branded formulations
- May be used prophylactically in certain surgical procedures to prevent postoperative infections
Common use
Ampicillin is indicated for the treatment of infections caused by susceptible strains of designated microorganisms. Common clinical applications include respiratory tract infections such as bronchitis and pneumonia, urinary tract infections including cystitis and pyelonephritis, gastrointestinal infections such as Salmonella typhi and Shigella, bacterial meningitis (often in combination with other agents like gentamicin or chloramphenicol), and septicemia. It is also employed for prophylaxis against bacterial endocarditis in high-risk patients undergoing dental or surgical procedures. Off-label uses may include treatment of Listeria monocytogenes infections in immunocompromised individuals.
Dosage and direction
Dosage must be individualized based on infection severity, pathogen susceptibility, renal function, and patient age.
Adults:
- Mild to moderate infections: 250–500 mg orally every 6 hours
- Severe infections: 1–2 g IV/IM every 4–6 hours
- Meningitis: 2 g IV every 4 hours
- Endocarditis prophylaxis: 2 g IM/IV 30 minutes before procedure
Pediatrics:
- 50–100 mg/kg/day in equally divided doses every 6 hours (oral/IV/IM)
- Meningitis: 200–400 mg/kg/day IV in divided doses every 6 hours
Renal impairment: Dosage adjustment required for creatinine clearance below 30 mL/min.
Oral doses should be taken on an empty stomach (1 hour before or 2 hours after meals) for optimal absorption. Complete the full prescribed course even if symptoms improve earlier.
Precautions
- Use with caution in patients with history of hypersensitivity reactions to penicillins, cephalosporins, or other beta-lactam antibiotics
- Monitor renal, hepatic, and hematopoietic function during prolonged therapy
- Superinfection with fungi or resistant bacteria may occur; discontinue use if superinfection is suspected
- Avoid in patients with mononucleosis due to high incidence of skin rash
- May cause false-positive urinary glucose tests when using copper reduction methods; use glucose oxidase methods instead
- Use during pregnancy only if clearly needed (Category B)
- Excreted in breast milk; use with caution in nursing mothers
Contraindications
- History of serious hypersensitivity reaction (e.g., anaphylaxis, Stevens-Johnson syndrome) to ampicillin or other penicillins
- Infectious mononucleosis
- Previous history of ampicillin-associated cholestatic jaundice/hepatic dysfunction
Possible side effect
Common (≥1%):
- Diarrhea
- Nausea
- Vomiting
- Rash
- Urticaria
Less common (<1%):
- Pseudomembranous colitis
- Glossitis
- Stomatitis
- Black “hairy” tongue
- Hepatitis
- Transient leukopenia
- Thrombocytopenia
- Eosinophilia
- Serum sickness-like reactions
- Interstitial nephritis
Rare:
- Anaphylaxis
- Seizures (especially with high doses in renal impairment)
- Candidiasis
Drug interaction
- Probenecid: Decreases renal tubular secretion of ampicillin, increasing and prolonging serum levels
- Allopurinol: Increases incidence of skin rash
- Oral contraceptives: May decrease efficacy; recommend alternative contraception during therapy
- Aminoglycosides: Synergistic against enterococci but physically incompatible when mixed in same IV solution
- Warfarin: May potentiate anticoagulant effect
- Methotrexate: May decrease renal clearance of methotrexate
- Bacteriostatic antibiotics (e.g., tetracyclines, chloramphenicol): May interfere with bactericidal action
Missed dose
Take the missed dose as soon as remembered. If it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not double the dose to make up for a missed one.
Overdose
Ampicillin overdose is primarily associated with neurological effects including seizures, especially in patients with renal impairment. Management is supportive and symptomatic. Hemodialysis may enhance elimination. Maintain hydration and electrolyte balance. Monitor renal function closely.
Storage
- Store capsules and powder for oral suspension at controlled room temperature (20–25°C/68–77°F)
- Reconstituted oral suspension stable for 14 days at room temperature or refrigerated; discard after this period
- IV solutions should be used immediately after reconstitution; stability varies with diluent and concentration
- Protect from moisture and light
- Keep all medications out of reach of children
Disclaimer
This information is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment of medical conditions. Do not initiate, discontinue, or change dosage of any medication without professional supervision. The prescribing information provided here may not be comprehensive or current.
Reviews
“Clinical experience spanning decades confirms ampicillin’s continued relevance in modern antimicrobial therapy. Its predictable pharmacokinetics and established efficacy profile make it particularly valuable in settings where resistance patterns remain favorable. While emerging resistance mechanisms necessitate careful susceptibility testing, ampicillin remains a workhorse antibiotic for many common community-acquired infections.” — Infectious Disease Specialist, 15 years experience
“From a primary care perspective, ampicillin offers an excellent balance of efficacy, safety, and cost-effectiveness for appropriate indications. The oral formulation is particularly useful for compliant outpatient therapy, though the frequency of dosing can present adherence challenges for some patients. The predictable side effect profile allows for confident prescribing with appropriate patient education.” — General Practitioner, 22 years experience
“Pharmacological studies continue to demonstrate ampicillin’s favorable tissue penetration characteristics, particularly in respiratory and genitourinary tissues. Its stability in gastric acid allows for reliable oral absorption, though food interaction requires careful patient instruction. The drug’s renal elimination pathway necessitates dosage adjustment in renal impairment but provides the advantage of dialyzability in overdose situations.” — Clinical Pharmacologist, 18 years experience