Demeclocycline calcium is a semisynthetic tetracycline antibiotic which was derived from a strain of Streptomyces aureofaciens. Demeclocycline binds to bacterial 30S ribosomal subunit and prevents binding of aminoacyl-tRNA to the mRNA-ribosome complex, thereby inhibiting protein synthesis. Demeclocycline also inhibits the effect of vasopressin on the renal tubules, thereby causing diuresis.