|
Drugs Highly Bound to Plasma Proteins Venlafaxine is not highly bound to plasma proteins; therefore, administration of Effexor XR to a patient taking another drug that is highly protein bound should not cause increased free concentrations of the other drug. Drugs that Inhibit Cytochrome P450 Isoenzymes CYP2D6 Inhibitors: Text Continues Below
In vitro and in vivo studies indicate that venlafaxine is metabolized to its active metabolite, ODV, by CYP2D6, the isoenzyme that is responsible for the genetic polymorphism seen in the metabolism of many ntidepressants. Therefore, the potential exists for a drug interaction between drugs that inhibit CYP2D6-mediated metabolism of venlafaxine, reducing the metabolism of venlafaxine to ODV, resulting in increased plasma concentrations of venlafaxine and decreased concentrations of the active metabolite. CYP2D6 inhibitors such as quinidine would be expected to do this, but the effect would be similar to what is seen in patients who are genetically CYP2D6 poor metabolizers (see Metabolism and Excretion under CLINICAL PHARMACOLOGY). Therefore, no dosage adjustment is required when venlafaxine is coadministered with a CYP2D6 inhibitor. The concomitant use of venlafaxine with drug treatment( s) that potentially inhibits both CYP2D6 and CYP3A4, the primary metabolizing enzymes for venlafaxine, has not been studied. Therefore, caution is advised should a patient's therapy include venlafaxine and any agent( s) that produce simultaneous inhibition of these two enzyme systems. Drugs Metabolized by Cytochrome P450 Isoenzymes CYP2D6: In vitro studies indicate that venlafaxine is a relatively weak inhibitor of CYP2D6. These findings have been confirmed in a clinical drug interaction study comparing the effect of venlafaxine with that of fluoxetine on the CYP2D6-mediated metabolism of dextromethorphan to dextrorphan. Page: << Prev | 1 | 2 | 3 | 4 | 5 | Next >>
|
.gif)
