Traditional drugs, such as antibiotics and blood pressure drugs, are called small-molecule agents because the active ingredient is usually a single, discrete chemical entity.
Biologic drugs are complex products that are derived from biologic sources (human, animal, microorganisms, or yeast). Biologics include viruses, genes, blood and body tissues, antibodies, toxins or antitoxins, vaccines, and related products used for treating disease. Until now, it has not been possible to develop generic versions of these products because of their complex manufacturing requirements and the difficulty in defining their exact composition.
The U.S. Food and Drug Administration (FDA) requires manufacturers to submit a proposed product for approval as a biosimilar drug or an interchangeable drug, rather than as a generic equivalent. Biosimilars are very similar to the original brand-name biologic drug they are compared to. Only minor differences in clinically inactive components are allowable in biosimilar products. Interchangeable drugs, additionally, are expected to provide the same benefits and risks as the original brand name biologic. Zarxio is a biosimilar drug to filgrastim (a drug used in cancer patients to help maintain their white blood cell counts). It is the first drug approved by the FDA as a biosimilar, not as an interchangeable, product. This means that Zarxio may be prescribed by a doctor, but it cannot be substituted (interchanged) for filgrastim by a pharmacist without the approval of the prescribing doctor.
Ongoing scientific developments may allow the creation of generic biologic products in the next several years. The advantage of generic biologic drugs for manufacturers, pharmacies, and consumers is that they could be freely interchanged and compete against one another for inclusion on a hospital or health plan drug list. Having different brands of very similar biologic products, as with epoetin, a hormone to increase red blood cell count, does not offer all the benefits of generically equivalent products.
(See also Overview of Generic Drugs and Drug Naming.)