by Chris Bojrab, MD
As we look for ways to contain the spiraling increases in the cost of healthcare, one area of potentially significant savings is generic medication. However, there are a number of misconceptions about generic medications among both patients and healthcare providers.
A generic drug is defined by the FDA as “a drug product that is comparable to brand/reference listed drug product in dosage form, strength, route of administration, quality and performance characteristics, and intended use.”
Generic drugs must contain the same active pharmaceutical ingredient (API), which is the chemical that provides the desired pharmacologic effect. Generic medications may differ in the non-API components, called excipients, which include binders, fillers, coatings, sweeteners, disintegrants, coloring agents, preservatives, etc.
The pharmacokinetics of a medication are studied in patients by giving a group of test subjects a known dose of the drug under standardized conditions, then checking serial blood levels of the medication at known time intervals. This information is used to establish standard parameters such as the Cmax (maximum serum concentration, usually expressed in ng/ml), the Tmax (length of time to reach the maximum serum concentration), T1/2 (half life or length of time for the medication level to drop to 50% of the Cmax), and AUC (the area under the curve, which is calculated using integral calculus and reflects the total dose exposure to the drug).
Understanding both the pharmacodynamics and pharmacokinetic actions of the medication allows us to determine the minimum effective concentration (MEC) and the maximum tolerated concentration (MTC). The area between the MEC and MTC is often referred to as the “therapeutic window”.
Generic medications are regulated in similar ways to brand name medications. Since the efficacy and safety of the API was established by the manufacturer of the brand name version of the medication, generic manufacturers are typically only required to demonstrate the “bioequivalence” of their product. Bioequivalence refers to the rate and extent of absorption of the generic compared to the name brand of the medication. Basically, it is a way of comparing the pharmacokinetic profile of the generic to the brand name medication.
According to the FDA and most of its counterparts in other countries, variability of up to 20% is not felt to be clinically significant for most patients. Per the FDA regulations, a generic is said to be bioequivalent if the 90% confidence intervals for the ratios of the average Cmax and AUC of the generic is within 80% to 125% of that of the brand name medication.
So, what is the bottom line? Based on my understanding of the science and nearly twenty years of clinical experience, I think that it is safe to say that most generic medications work perfectly well for most patients, but that they are not identical and therefore do not work exactly the same for every patient. There may be patients where the a precise blood level is more important (for a patient on a dose that is just barely therapeutic for them, or for a patient taking a medication with a more narrow therapeutic window) and for whom a change to a generic or a change from one generic to another may cause a clinically relevant difference.
However, I am always suspicious of patients who report that they cannot take generics in general, as there is not a plausible reason to explain why all generics (different categories and classes of medications) would be problematic for a given patient.
For more detailed information, I would recommend the excellent article by Scott Gavura on the Science Based Medicine blog at http://www.sciencebasedmedicine.org/generic-drugs-are-they-equivalent/
How do you handle generics in your clinical practice?
Chris Bojrab, MD, is the president of Indiana Health Group, the largest multidisciplinary behavioral health private practice in Indiana, established in 1987. He is a board certified psychiatrist and a Distinguished Fellow of the American Psychiatric Association who treats child, adolescent, adult, and geriatric patients. His areas of interest include psychopharmacology, sleep disorders, and gambling addiction. For more information and disclosures, visit www.chrisbojrabmd.com
The views expressed on this blog are solely those of the blog post author and do not necessarily reflect the views of Psych Congress Network or other Psych Congress Network authors.