Generally a pharmacist cannot be held liable to someone injured by a prescribed drug unless he or she failed to fill a prescription exactly as prescribed by a physician. An exception to this general rule is when the prescription is so clearly contraindicated that "ordinary prudence" imposes a duty on the pharmacist to verify facts with the physician, patient history on record with the pharmacy and/or the patient/customer. An example of this is when a pharmacist was aware that a prescribed drug was contraindicated given the known medical history of a particular customer. Burton v Sciano, 110 A.D.3d 1435  A pharmacist may have far greater knowledge of a patient's current medication regimen (to determine adverse drug interaction) than the emergency room physician who prescribed the contraindicated medication having a single encounter with the patient.
In the case of a pharmacist, nurse or auto mechanic, one who undertakes to render specialized services is: "held to the level of skill and care used by others in the community who practice the same profession or trade." The public policy rationale behind this concept recognizes that the duty of care required is proportionate to the degree of danger or risk involved. On the one hand we don't allow or expect pharmacists to practice medicine, but on the other hand we do expect them to catch some but not all of the errors committed by physician's. "A pharmacist's education and expertise will require that he or she do more to help protect their patrons from risks which pharmacists can reasonably foresee." Abrams v Bute, 138 A.D.3d 179