The type 2 supplemental approval of tiamulin is the third of its kind since retapamulin was approved for humans in 2007. Each of these approvals was an opportunity for FDA to require drug sponsors to provide microbial safety data related to antimicrobial resistance. Yet in each case the Agency failed to act. The signatories to this letter are asking that FDA change its policy and evaluate the microbial safety related to antimicrobial resistance of all new approvals of medically important antimicrobial drugs including type 2 supplementals.