Ampicillin

Systematic (IUPAC) name

7-(2-amino-2-phenyl-acetyl)amino-3 ,3-dimethyl-6-oxo-2-thia-5-azabicyclo [3.2.0]heptane-4-carboxylic acid

Formula C16H19N3O4S
Mol. mass 349.406 g/mol

Pharmacokinetic data

Protein binding 15 to 25%
Protein binding 15 to 25%
Metabolism 12 to 50%
Half life approx 1 hour
Excretion 75 to 85% renal
Bioavailability 40% (oral)

Ampicillin is a beta-lactam antibiotic that has been used extensively to treat bacterial infections since 1961. It is considered part of the aminopenicillin family and is roughly equivalent to amoxicillin in terms of spectrum and level of activity.[1] It can sometimes result in allergic reactions that range in severity from a rash (e.g. patients with mononucleosis) to potentially lethal anaphylaxis.

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. Transpeptidase is needed by bacteria to make their cell walls.[1] It inhibits the third and final stage of bacterial cell wall synthesis, which ultimately leads to cell lysis.
All Pseudomonas and most strains of Klebsiella and Aerobacter are considered resistant.

Use in research
Ampicillin is often used as a selective agent in molecular biology 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 on a medium containing ampicillin. 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.
From : Wikipedia