Posted by Sunnely on July 15, 2000, at 22:56:57
In reply to generic medications, posted by CarolAnn on July 15, 2000, at 18:59:10
> Ya'll be careful 'out there'. CarolAnn
Indeed. Please allow me to express my 2-cents about generic substitutions.
Except for certain restrictions, generic substitution is performed routinely in almost every pharmacy in America. Of course, HMOs love generics for one reason alone which I'm sure everyone knows.
There are at least 4 scenarios wherein generic substitution can take place: 1) a new prescription is written for a brand-name product filled with a generic; 2) a prescription previously filled with a brand-name product is refilled with a generic; 3) a prescription previously filled with a generic is refilled with the brand-name product (rarely happens with HMOs), and 4) a prescription previously filled with one generic is refilled with a generic from a different manufacturer (the most frequent type of generic substitution).
For a generic product to be approved by the FDA as bioequivalent or "similar" to its brand-name counterpart, the mean rate and extent of absorption of the generic drug must fall within -20% and +25% of the mean bioavailability measures for the brand-name product. What this means is that a generic drug could be no less than 20% bioequivalent or no more than 25% bioequivalent of the brand-name drug. This could lead to either lack of effectiveness or increased side effects, respectively. The FDA is responsible for testing the "bioavailability" of generic drugs. However, these studies are done on a small number of normal volunteers and can miss subtle effects. This rule of generic substitution does not usually present major problems but the potential exists. For example, if an epileptic person stable on a brand-name anti-epileptic Tegretol is substituted to the generic drug (carbamazepine), it may increase chance of breakthrough seizures. Another scenario is the substitution of drugs with narrow therapeutic index or NTI (the margin between safe therapeutic blood level and toxic blood level). For example, a person stable on a blood thinner Coumadin (brand name) may experience bleeding episodes including brain hemorrhage or the opposite, formation of clots, if the generic drug (warfarin) is substituted.
The fourth scenario of generic substitution mentioned above is actually the form that a patient is most likely to experience. This may present an even greater problem than the other forms of generic substitutions. A significant and even potentially serious change in bioequivalence may occur between generic drugs by different manufacturers. This is the reason why it is very important to stay with the same generic drug manufacturer if you find a specific generic drug that works well for you.
The following cases illustrate example of problems encountered with generic drug substitution (clonazepam or Klonopin):
1) A 63-year-old woman with nocturnal panic attacks and recurrent major depression had been stabilized on 1.5 mg of clonazepam and 40 mg Prozac for more than two years. At that time, she refilled her prescription for clonazepam and developed dizziness and fatigue. She had received a new generic form of clonazepam. When she was restarted on the brand form of the drug, her fatigue and dizziness resolved within 24 hours.
2) A 38-year-old woman with an eight-year history of panic disorder who had taken alprazolam (Xanax) in the past had been medication-free for several years. She experienced a return of spontaneous panic attacks and started taking 0.5 mg clonazepam, which relieved her symptoms. When the patient went to get her prescription refilled, the pharmacist switched her from the brand name to the generic form of the drug. The next day, the patient noticed an increase in her symptoms, such as anticipatory anxiety.
The author of the these case reports says that the 2 cases suggest that the generic and brand name forms of clonazepam may have "subtle differences in bioavailibity" that may cause differences in clinical response.
Reference: Case reports from Journal of Clinical Psychopharmacology 1997;17:425.
poster:Sunnely
thread:40585
URL: http://www.dr-bob.org/babble/20000708/msgs/40607.html