Amoxicillin is a ß-lactam bactericidal antibiotic. It inhibits biosynthesis of bacterial cell wall through inhibition of the synthesis of peptidoglycan, rendering cell more fragile and, therefore, unable to support endocellular osmotic pressure and, therefore, subject to lyses.

The main mechanism of bacterial resistance to the amoxicillin is the production of ß-lactamases, enzymes that in this way cause the inactivation of the antibacterial via hydrolysis of the ß-lactam ring obtaining penicilloic acid, stable but inactive compound. Resistance to ß-lactams can be transferred horizontally via plasmids or vertically (genes localized on bacterial chromosome). Cross-resistance between the amoxicillin and other penicillin exists, particularly, with other aminopenicillins (ampicillin).

In the pig, per os administration has a bioavailability of 47%, reaching the maximum serum concentration of 3 µg/ml one hour after the injection. After the administration per os, the plasma concentration (>2.5 µg/ml) is obtained in 1.5-2 hours. Amoxicillin is well distributed in the entire organism, reaching high concentrations in muscle, liver, gastrointestinal tract and kidney because of low percentage of plasmatic protein binding (17- 20%). It is little distributed in brain and spinal fluids, except when meninges are inflamed.

The metabolism of the amoxicillin is limited to the hydrolysis of the ß-lactam ring, which leads to inactive penicilloic acid liberation (20%). The biotransformation takes place in the liver.

Amoxicillin crosses the placental barrier. It is metabolised to a small extent; it is excreted mainly by the urine, and in smaller proportion by milk and bile (enterohepatic cycle).