Generic drugs are often considerably cheaper than the brand name product. Although a generic drug may have the same amount of active ingredient and undergone testing for bioequivalence, sometimes a patient will show a suboptimal response when using these agents. One should never assume that a generic will work as well as one would hope.


Common problems explaining why a generic drug may not work as well as the brand name:

(1) reduced bioavailability, resulting in lower peak concentration

(2) rapid absorption with early peak concentration and excretion, with subtherapeutic levels towards the end of the dosing interval


Situations when a generic should be investigated for therapeutic effectiveness:

(1) special release formulation (time-released, extended release, etc)

(2) known problem with generic formulation (such as coumadin, phenytoin, etc)

(3) inadequate therapeutic response

(4) drug with a low therapeutic index and/or narrow therapeutic range

(5) patient likely to have a problem with drug absorption or excretion (short bowel, dialysis, etc)

(6) critical drug for the patient


How to investigate:

(1) clinical monitoring of effectiveness (blood pressure, pain control, etc)

(2) therapeutic drug monitoring (peak and trough levels, kinetic curve)

(3) consulting with a pharmacist knowledgable about generic drugs

(4) check the current edition of the FDA's "Approved Drug Products with Therapeutic Equivalence Evaluations"


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