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"
