In recent years, increasing numbers of drugs have been created through processes that differ from the older, traditional methods. The terms used to describe these drugs all start with the prefix "bio." Here is a guide to understanding and differentiating between these terms.

Biologic.Biologic or biological products (commonly called biologics) are generally made from human or animal materials (or both), in contrast to most traditional prescription drugs, which are made through chemical processes. The chemical structure of most biologics is larger and more complex than that of typical prescription drugs. There are several types of biologic products: vaccines, blood and blood components, allergenics, somatic cells, tissues, proteins, and agents used in gene therapy.

Biosimilar. A biosimilar product is similar to an existing biologic product that has been approved by the Food and Drug Administration (FDA). The term was defined under the Biologics Price Competition and Innovation Act of 2009. Under the act there must be data showing that the product is "highly similar" to the approved biologic. There must be no clinically meaningful differences in terms of safety, purity, and potency, although there could be minor differences in "clinically inactive components." Most "biosimilars" can't be dispensed without a prescription for that particular drug. A few, however, might be considered interchangeable, meaning they could be substituted for the original product without increasing the risk of adverse effects or a decrease in efficacy; this substitution could be made by the pharmacist without a prescriber's order. Pharmacists will be responsible for knowing which biosimilar products require a prescriber's order. Currently, all biosimilars and interchangeable biologics are still under development; none is currently on the market.

So is a biosimilar the same thing as a generic? No. Biosimilar products are similar to other biologic products. The term generic refers only to "small-molecule" drugs. Generics must have the same active ingredient or ingredients, previously approved conditions of use, dosage form, strength, route of administration, and (with certain exceptions) labeling as the reference drug. The generic drug and the brand name drug must also be bioequivalent (see below).

Bioequivalent. A bioequivalent drug is the pharmaceutical equivalent of another drug, with bioavailability (see below) comparable to that of the reference drug. For drugs to be considered pharmaceutically equivalent, they must contain the same active ingredient or ingredients, the same amount (dose), the same route of administration, and the same strength or concentration. Pharmaceutical equivalents may differ from the original approved drug in characteristics such as shape, scoring, mechanism of action, packaging, colors, flavors, preservatives, and expiration time.

Bioavailability has to do with the pharmacokinetics of a drug. The term refers to the rate at which and extent to which the active ingredient is absorbed into the body and is made available at the intended site of drug action.

NPs who prescribe bioequivalent drugs should realize that there may be some individual variation in response to medications that's unrelated to the active ingredient. On some rare occasions, dyes and other inactive ingredients in bioequivalent products have produced allergic responses or a loss of therapeutic response. Patients' responses to such medications should be monitored. If undesired responses occur, the NP should specify the original product on the prescription. Pharmacists must also be familiar with the differences between bioequivalent products and inform patients when one product is substituted for another.

For more information on these terms and concepts, see FDA Drugs; Development and Approval Process: Biosimilars at http://1.usa.gov/1kS8MXT and the preface to the Orange Book: Approved Drug Products with Therapeutic Equivalence Evaluations: http://1.usa.gov/1l6Pxi4.