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Ampicillin: Wikis


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Systematic (IUPAC) name
(2S,5R,6R)-6-([(2 R)-2-amino-2-phenylacetyl]amino)
carboxylic acid
CAS number 69-53-4
ATC code J01CA01 S01AA19 QJ51CA01
PubChem 6249
DrugBank APRD00320
ChemSpider 6013
Chemical data
Formula C 16H19N3O4S 
Mol. mass 349.41 g·mol−1
SMILES eMolecules & PubChem
Pharmacokinetic data
Bioavailability 40% (oral)
Protein binding 15 to 25%
Metabolism 12 to 50%
Half life approx 1 hour
Excretion 75 to 85% renal
Therapeutic considerations
Pregnancy cat. A (Au), B (U.S.)
Legal status
Routes Oral, intravenous
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Ampicillin is a beta-lactam antibiotic that 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. Ampicillin 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 non-in allergic rash (in the case of patients that may unwitting have mononucleosis) to potentially lethal allergic reactions such as anaphylaxis. However, as with other penicillin drugs, it is relatively non-toxic and adverse effects of a serious nature are encountered only infrequently.


Mechanism of action

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 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 a competitive 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.

Effects on chloroplasts division

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 Lycopersicon esculentum L. (tomato) [2].


Ampicillin is closely related to amoxicillin, another type of penicillin, and both are used to treat urinary tract infections, otitis media, uncomplicated community-acquired pneumonia, Haemophilus influenzae, 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 the Staphylococcus aureus bacterium. Of concern is the number of bacteria that become resistant to Ampicillin necessitating combination therapy or use of other antibiotics.

All Pseudomonas and most strains of Klebsiella and Aerobacter are considered resistant.[3]

Use in research

Ampicillin is often used as a selective agent in molecular biology to select for and to confirm the uptake of genes (e.g., of plasmids) by bacteria (e.g., E. coli). A gene that is to be inserted into a bacterium is coupled to a gene coding for an ampicillin resistance (in E. coli, usually the bla (TEM-1) gene, coding for β-lactamase). The treated bacteria are then grown in a medium containing ampicillin (typically 50–100 mg/L). Only the bacteria that successfully take up the desired genes become ampicillin resistant, and therefore contain the other desired gene as well. It can be used with Cloaxicillin as well. As a powder ampicillin is white with slight yellow cast and is soluble in water (150 mg/ml).


  1. ^ a b AHFS DRUG INFORMATION 2006 (2006 ed.). American Society of Health-System Pharmacists. 2006.  
  2. ^ Britta Kasten und Ralf Reski (1997): β-lactam antibiotics inhibit chloroplast division in a moss (Physcomitrella patens) but not in tomato (Lycopersicon esculentum). Journal of Plant Physiology 150, 137-140. [1]
  3. ^ Mosby's Drug Consult 2006 (16 ed.). Mosby, Inc.. 2006.  

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