[Doxycycline].

Doxycyclin is a semi-synthetic structural isomer of the tetracycline family. It exhibits good intra-cellular penetration, with bacteriostatic activity on many bacteria. Different types or bacterial resistance are known. Acquired resistance has a ribosomal or a plasmidic mechanism. Resistance of Propionibacterium acnes is secondary to a mutation of ARNr. Doxycyclin also has an anti-inflammatory activity, via numerous pathways. Doxycyclin is rapidly and almost completely absorbed by the digestive tract. Food has no incidence on the absorption. It has a high but labile affinity for proteins with 90 p. 100 of the molecule linked. It rapidly diffuses in the extravascular compartment and in most of the tissues. Bile excretion is the main excretion route. It occurs more slowly by the kidney with tubular reabsorption. The main dermatological indication is acne with daily dose varing between 50 mg and 100 mg. Although good assays are lacking, a large professional consensus has validated its use. It is also active at the same dosage in rosacea. Chlamydial and mycoplasma urethritis may be treated by doxycyclin, and this antibiotic is presently used as second choice. Many other diseases may be treated as a primary or secondary choice, such as treponematoses, brucellosis, pasteurellosis, borreliosis, rickettsioses and cholera. Some non infectious diseases have been occasionally treated by doxycycline. Digestive side effects are the more frequent. Esophageal toxicity has been reduced with tablets and sufficient concomitant water ingestion. Phototoxicity is dose-dependent. Various cutaneous side effects have been described, some of them severe. Systemic toxicity is rare. Pregnancy is a contra-indication, and as other tetracyclines, it should not be given to children and during lactation. Doxycycline is commercialized as tablets. No reduction of the dose is necessary in renal failure. Association with retinoids is not recommended. Anticoagulants are potentialized. Didanosin, iron, and mineral salts lower its activity.