Provided herein are methods of determining NAT acetylation status of a subject with a 3,4-DAP-sensitive disease, methods of selecting a dose of 3,4-DAP or a pharmaceutically acceptable salt thereof adjusted to a subject's acetylation status, methods of administering 3,4-diaminopyridine or a pharmaceutically acceptable salt thereof to a patient in need thereof, and methods of treating 3,4-DAP sensitive diseases.