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|Systematic (IUPAC) name|
|Pregnancy cat.||A (Au), B (U.S.)|
|Protein binding||15 to 25%|
|Metabolism||12 to 50%|
|Half-life||approx 1 hour|
|Excretion||75 to 85% renal|
|ATC code||J01 S01 QJ51|
|Mol. mass||349.41 g·mol−1|
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Ampicillin is a beta-lactam antibiotic that is part of the aminopenicillin family and is roughly equivalent to its successor, amoxicillin in terms of spectrum and level of activity.1 It can sometimes result in reactions that range in severity from a rash (in the case of patients who may unwittingly have mononucleosis) to potentially lethal allergic reactions such as anaphylaxis. However, as with other penicillin drugs, it is relatively nontoxic, and adverse effects of a serious nature are encountered only rarely.
Belonging to the penicillin group of beta-lactam antibiotics, ampicillin is able to penetrate Gram-positive and some Gram-negative bacteria. It differs from penicillin G, or benzylpenicillin, only by the presence of an amino group. That amino group helps the drug penetrate the outer membrane of Gram-negative bacteria.
Ampicillin acts as an irreversible inhibitor of the enzyme transpeptidase, which is needed by bacteria to make their cell walls.1 It inhibits the third and final stage of bacterial cell wall synthesis in binary fission, which ultimately leads to cell lysis. Ampicillin has received FDA approval for its mechanism of action.
Ampicillin, like other β-lactam antibiotics, not only blocks the division of bacteria, but also the division of chloroplasts of the glaucophytes (called cyanelles) and chloroplasts of the moss Physcomitrella patens, a bryophyte. In contrast, it has no effect on the plastids of the higher-developed vascular plant Solanum lycopersicum (tomato).2
Ampicillin has a broad spectrum of activity and has been used to treat bacteria responsible for causing infections in the genitourinary and lower respiratory tract. The following represents ampicillin MIC susceptibility data for a few medically significant microorganisms.
- Escherichia coli: 0.5 μg/mL - 1024 μg/mL
- Haemophilus influenzae: 0.07 μg/mL - 128 μg/mL
- Streptococcus pneumoniae: 1 μg/mL - >50 μg/mL
Ampicillin is closely related to amoxicillin, another type of penicillin, and both are used to treat urinary tract infections, otitis media, H. influenzae infection, salmonellosis, and Listeria meningitis. It is used with flucloxacillin in the combination antibiotic co-fluampicil for empiric treatment of cellulitis, providing cover against group A streptococcal infection whilst the flucloxacillin acts against Staphylococcus aureus. Of concern is the number of bacteria that have become resistant to ampicillin, necessitating combination therapy or use of other antibiotics.
All Pseudomonas species and most strains of Klebsiella and Aerobacter are considered resistant.4 Additionally, resistance to ampicillin is seen in enterobacter, citrobacter, serratia, indole-positive proteus species, and other hospital-acquired gram negative infections.5
An ampicillin resistance gene (abbreviated ampR) is commonly used as a selectable marker in routine biotechnology. Due to concerns over horizontal gene transfer to pathogenic organisms in the wild, the European Food Safety Authority restricts use of this gene (among other resistance genes) in commercial genetically modified organisms. The enzyme responsible for degrading ampicillin is called beta-lactamase, in reference to the beta-lactam structure of ampicillin and related drugs.
Ampicillin has been used extensively to treat bacterial infections since 1961. Until the introduction of ampicillin by the British company Beecham, penicillin therapies had only been effective against Gram-positive organisms such as staphylococci and streptococci. Ampicillin (originally branded as 'Penbritin') also demonstrated activity against Gram-negative organisms such as H. influenzae, coliforms and Proteus spp. Ampicillin was the first of a number of so-called broad-spectrum penicillins subsequently introduced by Beecham.
- AHFS DRUG INFORMATION 2006 (2006 ed.). American Society of Health-System Pharmacists. 2006.
- Britta Kasten und Ralf Reski (1997): β-lactam antibiotics inhibit chloroplast division in a moss (Physcomitrella patens) but not in tomato (Solanum lycopersicum). Journal of Plant Physiology 150, 137-140. 
- Mosby's Drug Consult 2006 (16 ed.). Mosby, Inc. 2006.
- Katzung, Bertram G. (2007). Basic and Clinical Pharmacology, 10th edition. New York, NY: McGraw Hill Medical. p. 733. ISBN 978-0-07-145153-6.