Tetracycline is a linear tetracyclic broad spectrum antibiotic first prepared chemically by dechlorination of chlortetracycline and subsequently isolated from several Streptomyces species. Tetracycline has broad spectrum antibacterial and antiprotozoan activity, and acts by binding to the 30S and 50S ribosomal subunits blocking protein synthesis. Tetracycline is a pigment and, like many pigments, is degraded by light, oxygen, trace metal ions and pH variations. The purity of tetracycline is often variable, with significant levels of degradation products.