Amoxicillin binds to penicillin-binding protein 1A (PBP-1A) located inside the bacterial cell well. Penicillins acylate the penicillin-sensitive transpeptidase C-terminal domain by opening the lactam ring. This inactivation of the enzyme prevents the formation of a cross-link of two linear peptidoglycan strands, inhibiting the third and last stage of bacterial cell wall synthesis. Cell lysis is then mediated by bacterial cell wall autolytic enzymes such as autolysins; it is possible that amoxicllin interferes with an autolysin inhibitor.
Amoxicillin is a moderate-spectrum antibiotic active against a wide range of Gram-positive, and a limited range of Gram-negative organisms. It is usually the drug of choice within the class because it is better absorbed, following oral administration, than other beta-lactam antibiotics. Amoxicillin is susceptible to degradation by _-lactamase-producing bacteria, and so may be given with clavulanic acid to increase its susceptability. The incidence of _-lactamase-producing resistant organisms, including E. coli, appears to be increasing. Amoxicillin is sometimes combined with clavulanic acid, a _-lactamase inhibitor, to increase the spectrum of action against Gram-negative organisms, and to overcome bacterial antibiotic resistance mediated through _-lactamase production.
Serious toxicity is unlikely following large doses of amoxicillin. Acute ingestion of large doses of amoxicillin may cause nausea, vomiting, diarrhea and abdominal pain. Acute oliguric renal failure and hematuria may occur following large doses.