(a) A pharmacist who is requested to dispense a dangerous drug under a prescription issued by a practitioner shall determine, in the exercise of the pharmacist's professional judgment, that the prescription is a valid prescription. A pharmacist may not dispense a dangerous drug if the pharmacist knows or should have known that the prescription was issued without a valid patient-practitioner relationship.
(b) A pharmacist who is requested to dispense a dangerous drug under a prescription issued by a therapeutic optometrist shall determine, in the exercise of the pharmacist's professional judgment, whether the prescription is for a dangerous drug that a therapeutic optometrist is authorized to prescribe under Section 351.358, Occupations Code.