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Antibacterial.
Pharmacology: Pharmacodynamics: Doxycycline is mainly bacteriostatic and is thought to exert antimicrobial effects by binding to the 16S rRNA portion of the ribosome, preventing binding of tRNA to the RNA-30S bacterial ribosomal subunit, which is necessary for the delivery of amino acids for protein synthesis. Bacteriostatic antibiotics suppress the growth of bacteria, or keep them in the stationary phase of growth. It has a broad spectrum of activity against a variety of gram-positive and gram-negative microorganisms, treating numerous infectious diseases.
Pharmacokinetics: Doxycycline is readily absorbed and is bound to plasma proteins by varying degrees. It is almost completely absorbed after oral administration. This drug is highly lipid soluble and has a low affinity for calcium binding label. Absorption is not significantly affected by the concomitant ingestion of food or milk. Peak serum levels of approximately 2.6 mcg/mL are reached at 2 hours following a 200 mg tablet oral dose. Doxycycline diffuses readily into most body tissues, fluid and/or cavities and the volume of distribution has been measured as 0.7 L/kg.
It is metabolized in the liver and gastrointestinal tract and concentrated in bile. In patients with normal renal function, excretion of the active drug is about 30% to 40% in the urine with the remainder eliminated in the feces within 48 hours of dosage. Doxycycline 100 mg has a long half-life ranging from 18 hours after a single dose to 22 hours after repeated doses. Its high persistent serum levels are due to its low renal clearance. A longer-lasting antibiotic protection is hereby attained with just once a day or twice a day dosage of Doxycycline hyclate 100 mg.
