Posted by Larry Hoover on November 6, 2005, at 9:20:36
In reply to Re: Effexor-Zyrtec drug interactions, posted by Phillipa on November 5, 2005, at 23:30:21
> Still want to know what the difference in plain old effexor and effexor xr. fondly, Phillipa. ps I maan pharmacologically
The XR version has the drug bound up in little spheroids with pores of a set size. It takes time for the drug to dissolve out of the spheroids, where it is then available for uptake across the membranes of the intestine. From the monograph: "Drug release is controlled by diffusion through the coating membrane on the spheroids and is not pH dependent."
The lack of pH dependency means that the delayed release is not due to an enteric coating, which would only slightly delay release.
If you accept what the manufacturer claims, the XR version delivers the same amount of drug as the Immediate Release version, but just does so over a longer period. This would maintain a more stable blood concentration, and reduce the dosing frequency required to maintain stable blood concentration.
Lar
poster:Larry Hoover
thread:575801
URL: http://www.dr-bob.org/babble/20051106/msgs/575926.html