Tetracyclines are antimicrobial agents that interact with bacterial ribosomes and block protein synthesis. They have activity against a wide range of gram positive, gram-negative, anaerobic and aerobic bacteria, cell-wall free myco plasmas, chlamydiae, mycobacteria, rickettsia, Helicobacter, Listeria, and protozoan parasites, such as Entamoeba histolytica, Gzardia lamblia, and Plas modiumfalciparum 1-6. Tetracyclnes have been extenstvely used in humans for therapy of bacterial respiratory and urogenital tract diseases, as well as perrodontal, Lyme, and rtckettsial diseases. They are also used for therapy in animals and as growth promoters for animal food produciton (1), Tetracyclines were the first major group of antibrotrcs to which the term "broad-spectrum" was applied. Because of this spectrum of actrvity, their relative safety and low cost, tetracyclines have been widely used throughout the world, and are second after the penicillins in world consumption (7).