Snapshot A 33-year-old man presents to the emergency department for fever, headache, and rash. His symptoms are accompanied by myalgias and malaise and began approximately 3 days ago. He returned from a trip in North Carolina, where he believes he was bitten by a tick. He has no significant past medical history. He is severely allergic to penicillin and doxycycline. Physical examination is notable for a blanching erythematous rash with macules on the wrist and ankles. He is started on chloramphenicol. (Rocky Mountain spotted fever) Introduction Mechanism of action reversibly binds to the 50S ribosomal subunits, blocking peptidyltransferase and impairing protein synthesis bacteriostatic prevents bacterial reproduction Mechanism of resistance drug inactivation via a plasmid-encoded acetyltransferase Clinical use meningitis Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae Rocky Mountain spotted fever Adverse events aplastic anemia (dose independent) anemia (dose dependent) gray baby syndrome seen in premature infants due to their lack of liver UDP-glucuronosyltransferase