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In 2012, the FDA conceded that several generic antidepressant medications had never been tested and one was pulled from the market.
A company that makes a generic drug must show that its version of the drug is 80%-125% “bioequivalent” to the original brand name drug. For example: a brand name drug is taken and it is found that 100mg of medicine reaches the person’s bloodstream. For a generic version of the drug to be considered safe and effective, the active drug in the tablet or capsule must release between 80mg and 125mg reach the bloodstream (80-125%). This means that some companies might make generic versions that have 80mg reach the bloodstream and other companies might make generic versions that have 125mg reach the bloodstream. This difference isn’t a problem in most drugs. There are a few drugs, however, in which this can be an issue.
For example, some drugs are only safe and effective when the amount of medicine is within a small range in the bloodstream. This small range is called a “narrow therapeutic window.” This means that a small change in dose can cause a large change in the way the drug acts in the body. Below the therapeutic window, the drug is not effective. Above the therapeutic window, the drug could be harmful because too much drug is getting into the bloodstream. It is critical that the medicine be given in a dose that falls in the safe and effective range.
Let’s say a person is taking one of these drugs with a narrow therapeutic window. They have been taking a generic version of the drug that is 80% bioequivalent to the original brand name drug. After a few months, their pharmacy orders a generic version of the same drug that is made by a different company. This new version is 125% bioequivalent to the original brand name drug. This means that the new version of the drug could contain as much as 45% more active drug than the old version.
There are only a few drugs that have narrow therapeutic windows that need to be worried about. Some of these drugs include:
• Warfarin (used to prevent blood clots)
• Theophylline (used to improve breathing in people with asthma and other lung diseases)
• Phenytoin (used to prevent and treat seizures)
• Clonidine (used to treat high blood pressure)
• Quinidine (used to keep your heartbeat normal)
• Levothyroxine (used to treat low thyroid activity)
Most of the ingredients in a pill are not the active ingredient but other ingredients needed to hold the pill together, coat it, and control the way the pill delivers its drug in your body. These other ingredients can be different in a generic version of a drug. It is possible to have an allergic reaction or sensitivity to one of these ingredients. With some extended-release products, the brand name formula is still patented, so the generics may be completely different in their formulation. This can affect how fast or slow they release their drug and how this is affected by things like whether you take the pills with food or not.
FDA requires that the package inserts for generic drugs show the data (the “pharmacokinetic” data) from the brand name medication as if it is were based on the performance of the generic drug. In actuality, the data for the generic is typically different, but the FDA does not release this information.
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