Ampicillin: Price, Dosage & Where to Buy

Ampicillin is a penicillin antibacterial medicine used to treat infections caused by susceptible bacteria. It is most commonly prescribed for certain infections affecting the respiratory, genitourinary, or gastrointestinal tracts, and for meningitis. Ampicillin is available as a generic medicine and requires a prescription in the United Kingdom.

Ampicillin capsules are indicated for infections caused by susceptible bacteria. These include infections of the genitourinary tract, including gonorrhoea, and infections of the respiratory tract. It is also indicated for gastrointestinal infections caused by susceptible organisms, and for meningitis caused by Neisseria meningitidis.

The label states that treatment should be used only for infections that are proven or strongly suspected to be caused by bacteria. The organisms listed include certain strains of E. coli, Proteus mirabilis, enterococci, Shigella, Salmonella, Haemophilus influenzae, staphylococci, streptococci, Streptococcus pneumoniae, and Neisseria gonorrhoeae. Bacteriology studies can help identify the causative organism and whether it is susceptible to ampicillin.

Ampicillin is a penicillin antibacterial medicine in the beta-lactam group. It works by interfering with bacterial cell-wall formation. Bacteria need a strong cell wall to maintain their structure, particularly while growing and multiplying.

By blocking enzymes involved in building and maintaining that wall, ampicillin can cause susceptible bacteria to weaken and die. This action is directed at bacteria rather than viruses, so it does not treat viral illnesses such as ordinary colds.

Its effect depends on the infecting organism being susceptible to ampicillin. Some bacteria produce enzymes called penicillinases that can break down certain penicillins, which is why the label excludes infections caused by penicillinase-producing organisms.

The label lists oral capsules of 250 mg and 500 mg, as well as injectable powder formulations containing 125 mg, 250 mg, 500 mg, 1 g, 2 g, 10 g, 1 g/1 g, 2 g/2 g, 250 mg/250 mg, and 500 mg/500 mg, depending on the injection presentation. The usual starting dose is 500 mg four times daily for genitourinary or gastrointestinal infections in adults and children weighing over 20 kg. The usual starting dose is 250 mg four times daily for respiratory tract infections in that group.

The usual starting dose is 100 mg/kg/day total, divided four times daily, for genitourinary or gastrointestinal infections in children weighing 20 kg or less. The usual starting dose is 50 mg/kg/day total, divided three to four times daily, for respiratory infections in those children. The label lists administration at least one-half hour before or two hours after meals for maximal absorption.

A missed dose can reduce the regular exposure needed for an antibacterial medicine to work effectively. General pharmacy advice is to take the missed dose when remembered unless it is nearly time for the next scheduled dose, then omit the missed dose and continue the regular schedule.

Double doses should not be used to compensate. Advice from a pharmacist or prescriber is appropriate if several doses have been missed or symptoms are worsening.

Animal reproduction studies found no evidence of impaired fertility or harm to the fetus due to penicillin. There are no adequate and well-controlled studies in pregnant women, and animal findings may not predict human response.

The label states that penicillin should be used during pregnancy only if clearly needed. Pregnancy or breastfeeding decisions should be discussed with a doctor or pharmacist.

The label lists storage at 20°C to 25°C, protected in a tight container. Capsules should be kept as directed on the label to maintain quality and should be protected from unsuitable heat, moisture, and access by children.