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Prescribing via therapeutic substitution should be limited to drugs within the same therapeutic class

April 1, 2014

We have received several questions about adapting a prescription via therapeutic substitution, and it has come to our attention that some pharmacists are applying this authority very liberally. This authority must not be confused with initiating therapy or prescribing to manage ongoing therapy, which requires additional prescribing authorization.

The legislation and standards indicate that a pharmacist may adapt a prescription from another prescriber by substituting another drug that is expected to have a similar therapeutic effect. This type of adaptation should be limited to drugs within the same therapeutic class. Substituting a drug that employs a different pharmacologic action to achieve a similar therapeutic effect virtually always requires an assessment of the patient and a prescribing judgment. Prescribing based on the pharmacist’s own assessment of the patient requires additional prescribing authorization. 


  • While it may be appropriate for a pharmacist who does not have additional prescribing authorization to substitute one beta blocker for another or one proton pump inhibitor for another when filling a new prescription, it is not appropriate to substitute a beta-blocker for an ace inhibitor or vise versa when treating hypertension.
  • It is not appropriate for a pharmacist to substitute a topical product containing calcipotriol with one that also contains betamethasone when treating psoriasis.

These examples are prescribing decisions limited to pharmacists who have APA privileges.

Additional information

  • Prescribing by adaptation is allowed for new prescriptions only. Changing a prescription by therapeutic substitution at a refill is considered managing ongoing therapy which requires additional prescribing authorization.
  • Substituting a product that includes a combination of more than one drug when only one drug was initially prescribed would be considered initiating drug therapy which requires additional prescribing authorization.