Delivery Mechanism and Rate of Release May Be Different

Particularly with generic versions of time-release tablets (such as once-a-day formulations), the way in which the tablet releases active ingredient may be very different from that of the brand name drug. This is because the drug delivery technology used in the brand name drug may be proprietary and patent-protected, even though the patent on the active compound has expired.

As a result, each generic version of a time-release drug may employ a different drug release technology, consisting of different inactive ingredients and somewhat different rates of release of the drug. These different pills may be affected in a different way than the brand name drug when taken with foods or beverages. For example, when taken without food, a generic form of Wellbutrin XL 300 known as Budeprion XL 300 reaches a maximum blood level that is only 89% of that of brand name Wellbutrin. When taken with food, the opposite happens -- the maximum blood level with the generic is 110% of that of the brand name drug.

In addition to this food effect, Budeprion XL 300 releases drug much earlier than Wellbutrin XL 300. Dissolution laboratory testing by ConsumerLab.com showed the generic to release 34% of its drug in the first two hours while the original released only 8%. At four hours, the generic released 49% while the original released 25%. The FDA revealed that a similar effect is seen in human subjects – the generic reaches peak blood concentration 2 to 3 hours but the original peaks at 5 to 6 hours.
 
These differences are generally not noted in product literature, nor made publicly available. The FDA feels that these differences are not significant. The FDA does not typically release any of the bioequivalence data for generics, claiming that that information is proprietary to the manufacturer.  However, such information could be useful to consumers and physicians when it appears that a generic may not be performing like the brand name drug.