indication

For the treatment of infections of the ear, nose, and throat, the genitourinary tract, the skin and skin structure, and the lower respiratory tract due to susceptible (only b-lactamase-negative) strains of Streptococcus spp. (a- and b-hemolytic strains only), S. pneumoniae, Staphylococcus spp., H. influenzae, E. coli, P. mirabilis, or E. faecalis. Also for the treatment of acute, uncomplicated gonorrhea (ano-genital and urethral infections) due to N. gonorrhoeae (males and females).

pharmacology

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 β-lactamase-producing bacteria, and so may be given with clavulanic acid to increase its susceptability. The incidence of β-lactamase-producing resistant organisms, including E. coli, appears to be increasing. Amoxicillin is sometimes combined with clavulanic acid, a β-lactamase inhibitor, to increase the spectrum of action against Gram-negative organisms, and to overcome bacterial antibiotic resistance mediated through β-lactamase production.

mechanism of action

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.

toxicity

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.

biotransformation

Hepatic metabolism accounts for less than 30% of the biotransformation of most penicillins

absorption

Rapidly absorbed after oral administration.

half life

61.3 minutes

route of elimination

Most of the amoxicillin is excreted unchanged in the urine; its excretion can be delayed by concurrent administration of probenecid.

drug interactions

Demeclocycline: Possible antagonism of action

Doxycycline: Possible antagonism of action

Ethinyl Estradiol: This anti-infectious agent could decrease the effect of the oral contraceptive

Mestranol: This anti-infectious agent could decrease the effect of the oral contraceptive

Methacycline: Possible antagonism of action

Methotrexate: The penicillin increases the effect and toxicity of methotrexate

Minocycline: Possible antagonism of action

Oxytetracycline: Possible antagonism of action

Rolitetracycline: Possible antagonism of action

Tetracycline: Possible antagonism of action