Doxin Mechanism of Action

Pharmacology: Mechanism of Action: Doxycycline is primarily bacteriostatic but is also described as " bactericidal" in low concentrations against some bacterial species eg, Streptococcus pyogenes and Streptococcus pneumoniae.
Doxycycline inhibits bacterial protein synthesis. It binds principally to the 30s subunits of bacterial ribosomes and specifically inhibits the enzyme binding of aminoacyl-t-RNA to the adjacent ribosomal acceptor site.
Doxycycline also inhibits mammalian protein synthesis in higher concentrations.
Spectrum of Activity: Doxycycline exhibits in vitro activity against a wide range of gram-positive and gram-negative organisms. Cross resistance of these organisms to tetracyclines is uncommon.
Because many strains of groups of gram-positive and gram-negative microorganisms have been shown to be resistant to tetracycline, culture and susceptibility testing are recommended. Up to 44% of strains of Streptococcus pyogenes and 74% of Streptococcus faecalis have been found to be resistant to tetracycline drugs. Therefore, tetracycline should not be used for streptococcal disease unless the organism has been demonstrated to be susceptible.
Doxycycline has been found to be active against the asexual erythrocytic forms of Plasmodium falciparum but not against the gametocytes of Plasmodium falciparum.
Clinical Pharmacology: Doxycycline is completely absorbed (90 to 100%) after oral administration. Following a single 100 mg dose in fasting adults with normal renal function, peak serum concentrations are attained within 1.5 to 4 hours and average 1.5 to 2.1 μg/mL. A 200 mg dose produces peak serum concentrations of 2.6 to 3 μg/mL.
Doxycycline is highly lipid soluble and readily penetrates into the cerebrospinal fluid, brain, eye and prostate.
Doxycycline's serum half-life is 14 to17 hours after a single dose and 22 to 24 hours after multiple doses in patients with normal renal function. In patients with severe renal impairment, serum half-life is 18 to 26 hours after a single dose and 20 to 30 hours after multiple doses. Serum half-life of doxycycline is not altered in patients undergoing hemodialysis.
Doxycycline is excreted largely by nonrenal routes. Approximately 20 to 26% of a single oral or IV doxycycline dose is excreted in urine and 20 to 40% is excreted in feces within 48 hours as active drug in patients with normal renal function. In patients with creatinine clearances less than 10 mL/minute, the fraction of doxycycline excreted in urine within 72 hours may decrease to about 1 to 5%. Recent studies show that doxycycline is not metabolized in the liver but is partially deactivated in the intestine by chelate formation.
Spectrum of Activity: Doxycycline exhibits in vitro activity against a wide range of gram-positive and gram-negative organisms. Cross-resistance of these organisms to tetracyclines is uncommon.
Because many strains of groups of gram-positive and gram-negative microorganisms have been shown to be resistant to tetracycline, culture and susceptibility testing are recommended. Up to 44% of strains of Streptococcus pyogenes and 74% of Streptococcus faecalis have been found to be resistant to tetracycline drugs. Therefore, tetracycline should not be used for streptococcal disease unless the organism has been demonstrated to be susceptible.
Doxycycline has been found to be active against the asexual erythrocytic forms of Plasmodium falcifarum but not against the gametocytes of Plasmodium falciparum.