Composition and Formulation

Ampicillin is a beta-lactam antibiotic composed primarily of the active ingredient, ampicillin trihydrate. This formulation is available in oral capsules, oral suspensions, and as powder for injection. The capsule typically includes additional inactive ingredients, such as magnesium stearate and talc, to stabilize the compound and assist in its absorption. Oral suspensions may contain sodium benzoate and flavoring agents to enhance palatability. The injectable form may be prepared using sterile water for injection as a diluent, offering a concentrated form suitable for intravenous or intramuscular delivery.

Mechanism of Action

Ampicillin functions by inhibiting bacterial cell wall synthesis. It binds to penicillin-binding proteins within the bacterial cell wall, disrupting cross-linking of peptidoglycans, which are crucial for structural integrity. This disruption leads to cell lysis and, ultimately, the death of susceptible bacteria. Ampicillin is effective particularly against Gram-positive bacteria, and some Gram-negative bacteria, due to its ability to penetrate different bacterial cell walls.

Indications for Use

Ampicillin is prescribed for the treatment of a variety of infections. It is effective in treating respiratory tract infections such as pneumonia and bronchitis. Additionally, it is indicated for use in treating urinary tract infections and gastrointestinal infections, such as salmonella or shigella. Ampicillin is also employed in the treatment of infections caused by susceptible strains of enterococci, streptococci, and certain strains of E. coli. Further, it is used as a prophylactic agent against bacterial endocarditis in high-risk patients undergoing dental or surgical procedures.

Dosing and Administration

The dosing of ampicillin varies based on the type and severity of infection, patient’s age, and kidney function. For oral administration, typical adult dosing ranges from 250 mg to 500 mg every six hours. The oral suspension should be shaken well before each use and measured accurately. For intravenous or intramuscular administration, doses may range from 500 mg to 2 grams every four to six hours. Proper reconstitution of the injectable form is crucial. Dosage adjustments should be made for patients with renal impairment to prevent accumulation of the drug and potential toxicity.

Pharmacokinetics and Metabolism

Ampicillin is absorbed from the gastrointestinal tract when administered orally, but absorption is reduced by food intake. Its bioavailability ranges from 30% to 55%. Following oral administration, peak plasma concentrations occur within 1 to 2 hours. The drug is widely distributed in body tissues and fluids, including bile, synovial fluid, and pleural fluid, but less so into cerebrospinal fluid unless the meninges are inflamed. Ampicillin is excreted primarily through the kidneys, with approximately 30% to 50% of the administered dose eliminated unchanged in the urine. The half-life of ampicillin is approximately one to two hours in individuals with normal renal function.

Drug Interactions

Ampicillin may interact with other pharmaceutical agents, affecting its efficacy or safety profile. Concurrent use with allopurinol increases the risk of skin rash. The efficacy of oral contraceptives may be reduced when used in conjunction with ampicillin, increasing the risk of unplanned pregnancy. Probenecid can increase ampicillin levels by decreasing renal tubular secretion, extending the drug’s duration of action. When used with anticoagulants, ampicillin may affect coagulation tests, necessitating monitoring for potential excessive anticoagulation. Also, tetracyclines may inhibit its bactericidal activity if used simultaneously, reducing treatment effectiveness.

Contraindications and Precautions

Ampicillin is contraindicated in individuals with a known hypersensitivity to penicillins or cephalosporins. Special care should be taken in administering to patients with a history of asthma or other allergic conditions, as they may have an increased risk of hypersensitivity reactions. Patients with impaired renal function or those undergoing dialysis should receive adjusted doses due to altered drug excretion kinetics. Intrahepatic cholestasis may occur, leading to adverse hepatic effects; hence, liver function tests may be warranted during prolonged therapy.

Effects on Laboratory Tests

Ampicillin can potentially affect the outcomes of certain laboratory tests. For instance, it may lead to false-positive results in urinary glucose tests that rely on copper reduction methods. It may also cause erroneous readings in protein-bound iodine tests. The medication can influence liver function tests by altering alkaline phosphatase and transaminase levels, which should be considered when evaluating lab results. Potential leukopenia and thrombocytopenia during prolonged therapy necessitate regular monitoring of complete blood counts.

Adverse Effects

The administration of ampicillin may result in a range of adverse reactions. Common effects include gastrointestinal disturbances such as nausea, vomiting, diarrhea, and abdominal cramps. Hypersensitivity reactions can manifest as rashes, urticaria, or rarely, anaphylaxis. Hematologic effects, such as neutropenia, anemia, or thrombocytopenia, might occur but are less common. Hepatic challenges include transient rises in liver enzymes and cholestatic jaundice, particularly following prolonged therapy. Furthermore, non-specific nervous system effects, like headache or dizziness, may be reported by some individuals during treatment.