Pharmacology: Microbiology: Doxycycline is primarily bacteriostatic and is thought to exert its antimicrobial effect by inhibition of protein synthesis. Doxycycline is active against a wide range of gram-positive and gram-negative organisms. It is in the tetracycline class having similar antimicrobial spectra. Cross-resistance among tetracyclines is common.
Pharmacokinetics: Tetracyclines are readily absorbed and are bound to plasma proteins in varying degrees. They are concentrated by the liver in bile and excreted in the urine and faeces at high concentrations and in a biologically active form. Doxycycline is virtually completely absorbed after oral administration. Following a 200-mg dose, peak serum levels of 2.6 mcg/mL are reached in 2 hrs in normal adults. Excretion of doxycycline by the kidney is about 40%; serum half-life ranges between 18-22 hrs.