Amoxicillin, a semi-synthetic aminopenicillin, kills bacteria by interfering with the synthesis of the bacterial cell wall. It binds to penicillin-binding proteins on the bacterial cell wall and blocks peptidoglycan synthesis. Peptidoglycan is a heteropolymeric structure that gives cell wall its mechanical stability. The final stage of peptidoglycan synthesis involves the completion of the cross-linking with the terminal glycine residue of the pentaglycine bridge linking to the fourth residue of the pentapeptide. The transpeptidase that performs this step is inhibited by penicillins. The bacterial cell wall, thus weakened, leads to swelling and rupture of the microorganisms.
Amoxicillin is generally stable in the presence of acidic gastric secretions and well-absorbed after oral administration. Oral absorption of amoxicillin is 90% and peak serum level is 10 mg/L after a 500 mg oral dose. Peak levels are attained after 1-2 hours. Food has no significant influence on amoxicillin absorption.
Amoxicillin is widely distributed after absorption from the GI tract. The drug is generally distributed into ascitic, synovial and pleural fluids. Amoxicillin is distributed into middle ear effusions, bronchial secretions, sputum, maxillary sinus secretions, and tonsils. It is also distributed into liver, lungs, gallbladder, prostate, and muscle. Only minimal concentration of aminopenicillins including amoxicillin, are attained in the cerebrospinal fluid. Amoxicillin is 17-20 % bound to serum protein. It readily crosses the placenta; amoxicillin concentrations in cord blood are reportedly 25-33% of concurrent maternal serum concentrations.
Approximately 19-33% of a single oral dose of amoxicillin is excreted in urine as penicilloic acids. Like other penicillins, amoxicillin is excreted by renal tubular secretion and to a lesser extent by glomerular filtration. Small amounts of the drug are also excreted in feces and bile. Serum clearance of amoxicillin is reportedly 283 mL/minute. Serum half-life is generally inversely proportional to birthweight, gestational age and chronological age. The serum half-life of amoxicillin is reportedly 3.7 hours in full-term neonates and 0.9-1.9 hours in infants and children.
Amoxicillin is removed by hemodialysis; a 4 - 6 hour period of hemodialysis generally removes 30-40% of a single oral dose of the drug into the dialysate when the dose is given immediately prior to dialysis. Only minimal amounts of amoxicillin appear to be removed by peritoneal dialysis.
Microbiology: Antimicrobial Spectrum of Activity:
Amoxicillin has been shown to be active against most strains of the following microorganisms both in vitro
and in clinical infections: (See Table 1.)
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