How does the learned intermediary doctrine provide a shield against pharmacy malpractice, and what are its exceptions?

According to the learned intermediary doctrine, the individual who is in the best position to recommend or take precautions against the adverse effects linked to a prescription drug is the prescribing physician.  Vitanza v. Upjohn Co., 257 Conn. 365, 384, 778 A.2d 829 (2001)   This doctrine has not been extended to pharmacists and pharmacies but rather shields them from liability for dispensing medication prescribed a physician.  However, there are exceptions to this general rule, such as where a pharmacy has "specific knowledge of potential harm to specific persons in particular cases . . . ."  In that case, there is a duty to warn on the part of the pharmacy, and liability may be imposed for the consequences of its failure to do so.  Where the courts have held that pharmacies owe their clients a duty that goes beyond properly filling prescriptions, they have done so due to the presence of additional elements such as known contraindications, that would place a reasonably prudent pharmacist on notice of a potential problem.