Ampicillin

Ampicillin is a type of antibiotic from the aminopenicillin subgroup within the penicillin family. It is prescribed to both prevent and treat a range of bacterial infections, such as those affecting the respiratory tract, urinary tract, and the lining of the heart (endocarditis), as well as meningitis and salmonellosis. It can also be given to prevent group B streptococcal infection in newborns. The drug is available in oral forms, as an injection into a muscle, or through an intravenous line.

Side effects

Common side effects include rash, nausea, and diarrhea. People with a known penicillin allergy should not take it. More serious risks include Clostridioides difficile colitis and anaphylaxis. For those with kidney issues, a lower dose may be necessary.

Use during pregnancy and while breastfeeding is generally considered safe. First discovered in 1958 and introduced commercially in 1961, ampicillin is included on the World Health Organization's List of Essential Medicines and is classified by the WHO as critically important for human medicine. It is available as a generic medication.

Bacteria

Ampicillin is used to treat bacterial meningitis (often with an aminoglycoside to improve effectiveness against gram-negative bacteria), enterococcal endocarditis (frequently combined with an aminoglycoside, though this is an off-label use), gastrointestinal infections from contaminated food or water (e.g., Salmonella), genito-urinary tract infections, healthcare-associated infections from urinary catheters that do not respond to other drugs, otitis media, sepsis, respiratory infections (including bronchitis, pharyngitis), sinusitis, and whooping cough (to prevent and treat secondary infections). It is also used prophylactically in people with a history of rheumatic heart disease or those undergoing dental procedures, vaginal hysterectomies, or C-sections, and in pregnant women carrying group B streptococci to prevent early-onset neonatal infections. Ampicillin was once used for gonorrhea, but resistant strains are now too common. The drug works against many gram-positive and gram-negative bacteria.

It was the first broad-spectrum penicillin, effective against gram-positive organisms like Streptococcus pneumoniae, Streptococcus pyogenes, some Staphylococcus aureus (excluding penicillin-resistant or methicillin-resistant strains), Trueperella, and some Enterococcus. It is one of the few antibiotics active against multidrug-resistant Enterococcus faecalis and E. faecium. Against gram-negative bacteria, it targets Neisseria meningitidis, some Haemophilus influenzae, and some Enterobacteriaceae (though most Enterobacteriaceae and Pseudomonas are resistant). Its spectrum is widened when combined with sulbactam, which inhibits beta-lactamase.

Available forms

It is sometimes used with other antibiotics such as vancomycin, linezolid, daptomycin, and tigecycline. Ampicillin is given orally (as capsules or oral suspension), by intramuscular injection, or by intravenous infusion. The oral form is not used for initial treatment of severe infections but as a follow-up to injections. For injections, it is supplied as a powder that must be reconstituted.

Specific populations

IV injections must be given slowly, as rapid administration can cause convulsive seizures. Ampicillin is one of the most commonly used drugs in pregnancy and is considered generally harmless (U.S. FDA category B, Australian TGA category A). It is the drug of choice for treating Listeria monocytogenes in pregnant women, sometimes with an aminoglycoside. Pregnancy increases ampicillin clearance by up to 50%, so a higher dose may be needed.

It crosses the placenta, reaching 50–100% of maternal plasma levels in amniotic fluid, which can lead to high concentrations in the newborn. Only minimal amounts pass into breast milk. In newborns, the drug has a longer half-life and lower plasma protein binding, and kidney clearance is reduced due to immature kidney function. Ampicillin is contraindicated in people with penicillin hypersensitivity, as it can cause fatal anaphylaxis.

Hypersensitivity reactions may include frequent skin rashes, hives, exfoliative dermatitis, erythema multiforme, and a temporary decrease in red and white blood cells. It is not recommended for people with concurrent mononucleosis, as over 40% develop a skin rash. Ampicillin is relatively less toxic than other antibiotics.

Side effects are more likely in those sensitive to penicillins or with a history of asthma or allergies. Rare but severe side effects include angioedema, anaphylaxis, and C. difficile infection (ranging from mild diarrhea to serious pseudomembranous colitis). Some people develop a black, "furry" tongue. Other serious effects include seizures and serum sickness.

The most common side effects, occurring in about 10% of users, are diarrhea and rash. Less common effects include nausea, vomiting, itching, and blood dyscrasias. Gastrointestinal issues (hairy tongue, nausea, vomiting, diarrhea, colitis) are more common with the oral form. Some conditions may appear weeks after treatment ends.