A drug dispensed on a written or oral prescription of a practitioner licensed by law to administer such drug, except a drug dispensed in the course of the conduct of a business of dispensing drugs pursuant to diagnosis by mail, shall, if such drug bears a label containing the name and place of business of the dispenser, the serial number and date of filling or refilling of such prescription, the name of such practitioner licensed by law to administer such drugs and the name of the patient, be exempt from the requirements of section 21a-106, except that no prescription for a legend drug or any derivative of any legend drug, shall be refilled except upon the order of the practitioner licensed by law to administer such drug.