Ampicillin injection for bacterial infections

Ampicillin for injection is a synthetic penicillin antibiotic administered by injection. It is effective against a broad range of bacteria, including many Gram-positive and Gram-negative strains, and is used to treat various moderate to severe bacterial infections.

Ampicillin for injection is prescribed to treat infections caused by bacteria susceptible to ampicillin, including:

• Respiratory tract infections caused by Streptococcus pneumoniae, Staphylococcus aureus (both penicillinase and nonpenicillinase-producing strains), Haemophilus influenzae, and Group A beta-hemolytic streptococci.
• Bacterial meningitis caused by E. coli, Group B streptococci, Listeria monocytogenes, and Neisseria meningitidis. Aminoglycoside antibiotics may be added to enhance activity against Gram-negative bacteria.
• Septicemia and endocarditis from susceptible Gram-positive organisms (like Streptococcus spp., penicillin G-susceptible staphylococci, and enterococci) and Gram-negative sepsis due to E. coli, Proteus mirabilis, and Salmonella spp. Aminoglycosides can improve outcomes in streptococcal endocarditis.
• Urinary tract infections caused by sensitive strains of E. coli and Proteus mirabilis.
• Gastrointestinal infections including typhoid fever caused by Salmonella typhi and other Salmonella and Shigella species (dysentery).

Parenteral ampicillin is recommended for moderately severe or severe infections and patients unable to take oral antibiotics. Therapy should ideally be guided by culture and susceptibility results.

Ampicillin sodium

Ampicillin works by interfering with the formation of bacterial cell walls. It binds to specific proteins inside bacteria, inhibiting their ability to form cross-links in the cell wall peptidoglycan, which weakens the wall and leads to bacterial cell death. It is bactericidal against many Gram-positive and Gram-negative bacteria but can be destroyed by bacterial enzymes called penicillinases.

Adults and children weighing ≥40 kg:

• Respiratory and soft tissue infections: 250 to 500 mg every 6 hours.
• Gastrointestinal and genitourinary infections: 500 mg every 6 hours.
• Urethritis due to Neisseria gonorrhoeae: Two doses of 500 mg each, 8–12 hours apart. Repeat or extend treatment as needed.

Children weighing <40 kg:

• Respiratory/soft tissue infections: 25 to 50 mg/kg/day divided every 6 to 8 hours.
• Gastrointestinal/genitourinary infections: 50 mg/kg/day divided every 6 to 8 hours.

Bacterial meningitis (adults and children): 150 to 200 mg/kg/day in divided doses every 3 to 4 hours, initially by intravenous drip.

Neonates (≤28 days postnatal age): Dosage based on gestational and postnatal age; for example, ≤34 weeks gestational and ≤7 days postnatal: 100 mg/kg/day divided every 12 hours; other regimens adjust frequency and dose accordingly.

Treatment duration should continue at least 48 to 72 hours beyond symptom resolution or bacterial eradication; for Group A beta-hemolytic streptococci infections, a minimum of 10 days is recommended to prevent complications.

Administration: Ampicillin injection is prepared fresh and should be administered intramuscularly or intravenously within one hour of reconstitution. Intravenous dosing varies by vial strength and should be given slowly to avoid seizures.

Ampicillin injection is contraindicated in patients with a history of hypersensitivity to any penicillin.

Serious hypersensitivity reactions: Anaphylaxis, including fatal outcomes, can occur, especially in patients with prior penicillin allergy or other allergies. Cephalosporin cross-reactivity is possible. Emergency treatment with epinephrine, oxygen, steroids, and airway management is required for severe reactions.

Clostridium difficile-associated diarrhea (CDAD): Use of ampicillin may cause CDAD ranging from mild diarrhea to fatal colitis. CDAD can develop during or up to two months after antibiotic use. Prompt recognition and management including discontinuing non-CDAD-directed antibiotics and supportive care are critical.

Common: Skin rashes, urticaria, diarrhea (mostly with oral use), nausea, vomiting, stomatitis, glossitis.

Serious: Anaphylaxis, exfoliative dermatitis, erythema multiforme, linear IgA bullous dermatosis, pseudomembranous colitis, hematologic reactions (anemia, thrombocytopenia, leukopenia, eosinophilia, agranulocytosis), seizures, and transient liver enzyme elevations.

The occurrence of skin rashes is increased when ampicillin is given concurrently with allopurinol. Ampicillin excretion can be delayed by probenecid. False-positive urine glucose tests may occur with some chemical reagent tests; enzyme-based tests are recommended instead.

Pregnancy: Classified as Category B. Animal studies show no adverse fetal effects; however, adequate controlled studies in pregnant women are lacking. Use only if clearly needed.

Labor and delivery: It is unknown if ampicillin affects labor or the fetus in humans, though animal studies showed some uterine contractility changes.

Lactation: Ampicillin is excreted in trace amounts in human milk; use caution when administering to nursing women.

Overdose may cause seizures especially with rapid intravenous administration. Management includes stopping the drug and providing supportive measures; rapid infusion should be avoided to reduce seizure risk.

Store the dry powder at controlled room temperature, 20 to 25°C (68 to 77°F). Protect reconstituted solutions from freezing.