A synthetic, broad-spectrum tetracycline with antimicrobial activity. Doxycycline binds reversibly to the 30S ribosomal subunit and possibly to the 50S ribosomal subunit, blocking the binding of aminoacyl-tRNA to the mRNA-ribosome complex, which results in an inhibition of bacterial protein synthesis. In addition, this agent may inhibit collagenase activity. Check for active clinical trials using this agent. (NCI Thesaurus)