The debate over substitution policy. Its evolution and scientific basis.

Considerations about differences in bioavailability between brand-name drugs and generic formulations of these agents are discussed as are the meaning of drug quality, the national regulatory situation concerning generic substitution, and state-to-state variations in product selection laws. Actual and potential problems with generic substitution are described with regard to current and future prescribing practices. Proposed regulations permitting or mandating substitution of generic alternatives and therapeutic substitutes are mentioned. Although there is no consensus on the proper use of generic drugs, physicians should be aware of potential differences in bioavailability and therapeutic effectiveness that may arise when one drug product is substituted for another. Such differences are of particular concern for certain therapeutic categories such as psychotropic, cardiovascular, and endocrine/metabolic drugs, as well as for special population groups, such as the elderly, infants, and children. If physicians are to prescribe in an optimal manner, they should be knowledgeable about the bioavailability of different drug products and the national and state laws addressing substitution. Generic substitution is linked to current and future policy changes in the area of therapeutic substitution.