May 6th, 2008

Therapeutic substitution by pharmacists is the act of dispensing an alternative chemical entity from the same therapeutic class for the drug product prescribed by the doctor.  In simplest terms, it is switching a patient from one medication to a completely different medication than was originally intended by the prescriber.  i.e. Zantac (ranitidine) for Tagamet (cimetidine); Lipitor(atorvastatin) for Mavacor (lovastatin)

Therapeutic substitution is often confused with generic substitution, but actually is completely different.  Generic substitution is when a doctor prescribes a drug and leaves the choice of the brand to the pharmacist.  When this happens the patient essentially receives a different brand of the same medication, but it will always be the same generic name as the prescribed medication. 

Programs that have the ultimate goal of therapeutic substitution are making an assumption – that all medications in a therapeutic class are easily interchangeable.  In reality, each medication possesses unique chemical qualities that may work better for one patient than for another. 

In practice, therapeutic substitution without prescriber authorization rarely takes place in the outpatient setting.   Pre-authorized therapeutic substitution most often takes place in an inpatient setting.  There, problems that could result from the substitution presumably can be detected and more easily fixed, while this would not be possible in an outpatient setting.

The American Medical Association has written a policy position on therapeutic substation.