Doxycycline is a synthetic tetracycline derivative with similar antimicrobial activity. Doxycycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit. Doxycycline has bacteriostatic activity against a broad range of Gram-positive and Gramnegative bacteria. Doxycycline has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections.