If you have a question about generic substitution, consult the FDA’s Approved drug products with therapeutic equivalence evaluations4—also known as the “Orange Book,” which is available online (see Related Resources). This resource provides guidance about which drugs are interchangeable. The Orange Book is the “gold standard” on approved drug products and their interchangeability.
The Table lists certain psychiatric medications that may have issues with generic substitutions. Most pharmacies stock and dispense only generic drugs that the FDA considers bioequivalent to the brand-name product.
Allergic reactions may occur because of different inert ingredients within each generic or brand-name drug. Generic drug manufacturers are not required to use the same inactive or “filler” ingredients. Some patients may be allergic to 1 version and may require a specific brand or generic version to overcome this potential allergy.3
Although most generic substitutions occur without incident, consider BE differences among products and your patient’s medical condition before initiating a switch. When switching between generics, carefully monitor your patient as you would when switching from the brand-name product to a generic. If new treatment-related issues arise or lack of efficacy occurs, ask your patient if the pharmacy switched to a new generic formulation.
Table
Bioequivalence among generic psychotropics: What to know before you switch
| Medication | Comments |
|---|---|
| Amitriptyline/perphenazine | Generic formulations may not be interchangeable* |
| Anticonvulsants | Because these medications have a narrow therapeutic index when used for seizure disorders, patients are recommended to not switch formulations. When used for psychiatric disorders, the margin of safety is unknown and switching may be appropriate |
| Chlorpromazine | Generic formulations are not bioequivalent |
| Clozapine | Generic formulations may not be bioequivalent at all dosages* Dosage adjustments may be needed in patients who need to switch formulations during treatment |
| Venlafaxine | Some formulations may not be interchangeable* |
| *Consult the FDA’s Approved drug products with therapeutic equivalence evaluations to determine if generics are interchangeable | |
| Source: Reference 4 | |
- Food and Drug Administration. www.fda.gov/Drugs/default.htm.
- Generic Pharmaceutical Association. www.gphaonline.org.
- Food and Drug Administration. Orange book: approved drug products with therapeutic equivalence evaluations. www.accessdata.fda.gov/scripts/cder/ob/default.cfm.
Drug brand names
- Amitriptyline/Perphenazine • Triavil
- Chlorpromazine • Thorazine
- Clozapine • Clozaril
- Fluoxetine • Prozac
- Venlafaxine • Effexor
Disclosure
Dr. Ellingrod is a member of an advisory board for Eli Lilly and Company.