Except as provided in subsection (b) of this section, a person may not dispense a controlled dangerous substance without a written prescription or an electronic prescription from an authorized provider if the substance is: listed in Schedule II; and a drug to which § 21–220 of the Health – General Article applies. A controlled dangerous substance to which subsection (a) of this section applies may be dispensed without a written prescription or an electronic prescription by: an authorized provider who: is not a pharmacist; and dispenses the controlled dangerous substance directly to an ultimate user; or a pharmacist if: an emergency exists; the pharmacist dispenses the drug under regulations of the Department on an oral prescription that the pharmacist reduces promptly to writing and keeps on file; and federal law authorizes the oral prescription. A prescription for a controlled dangerous substance listed in Schedule II shall be kept on file in conformity with the requirements for records and inventories under § 5–306 of this title. A person may not refill a prescription for a controlled dangerous substance listed in Schedule II.