Effexor (venlafaxine HCl) tablets and Effexor XR (venlafaxine HCl) extended-release capsule
Detailed View: Safety Labeling Changes Approved By FDA Center for Drug Evaluation and Research (CDER)
Drug-Laboratory Test Interactions
- False-positive urine immunoassay screening tests for phencyclidine (PCP) and amphetamine have been reported in patients taking venlafaxine. This is due to lack of specificity of the screening tests. False positive test results may be expected for several days following discontinuation of venlafaxine therapy. Confirmatory tests, such as gas chromatography/massspectrometry, will distinguish venlafaxine from PCP and amphetamine.
CONTRAINDICATIONS (section is a revised version of the information previously found in WARNINGS)
- Effexor must not be used concomitantly in patients taking MAOIs or in patients who have taken MAOIs within the preceding 14 days due to the risk of serious, sometimes fatal, drug interactions with SNRI or SSRI treatment or with other serotonergic drugs. These interactions have been associated with symptoms that include tremor, myoclonus, diaphoresis, nausea, vomiting, flushing, dizziness, hyperthermia with features resembling neuroleptic malignant syndrome, seizures, rigidity, autonomic instability with possible rapid fluctuations of vital signs, and mental status changes that include extreme agitation progressing to delirium and coma. Based on the half-life of venlafaxine, at least 7 days should be allowed after stopping Effexor before starting an MAOI.