Pipacycline (mepicycline) is a semi-synthetic tetracycline formed by a Mannich condensation of formaldehyde and 4-hydroxyethylpiperazine with tetracycline. The introduction of the piperazine improves bioavailability, but Mannich bases are pro-drugs, converting back to the parent compound. Pipacycline is used commercially as a salt in combination with penicillin V for parenteral use (penimepicycline). The intrinsic in vitro activity and SARs for the amide region of the tetracycline molecule have not been investigated extensively. Pipacycline has not been extensively cited in the literature.