Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Venlafaxine is a serotonin and norepinephrine reuptake inhibitor approved for treatment of major depression, anxiety and panic disorders, and social phobias. It is also used for bipolar disorder, bulimia, post-traumatic stress, obsessive behavior, and attention-deficit disorder. Venlafaxine is converted by CYP2D6 to the active metabolite, O-desmethylvenlafaxine. The therapeutic range for venlafaxine includes measurement if O-desmethylvenlafaxine; optimal response is seen when combined concentrations of parent and metabolite are between 195 and 400 ng/mL. Venlafaxine is significantly affected by reduced hepatic function, but only slightly by reduced renal function.
Average elimination half-lives are 5 hours for venlafaxine and 10 hours for O-desmethylvenlafaxine, which are much shorter than many other antidepressants. For this reason, extended release formulations are available. Time to peak serum concentration is 2 hours for the regular product and 8 hours for the extended release product. Common toxicities are mild, including drowsiness, dizziness, nausea, and headache.
Monitoring serum concentration during therapy
Evaluating potential toxicity
The test may also be used to evaluate patient compliance.
Most individuals display optimal response to venlafaxine when combined serum levels of venlafaxine and O-desmethylvenlafaxine are between 195 and 400 ng/mL. Some individuals may respond well outside of this range, or may display toxicity within the therapeutic range, thus interpretation should include clinical evaluation. Risk of toxicity is increased with combined levels >1,000 ng/mL. Therapeutic ranges are based on specimens drawn at trough (ie, immediately before the next dose).
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Serum must be separated from cells within 2 hours of draw. Specimens that are obtained from gel tubes are not acceptable.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Venlafaxine + O-desmethylvenlafaxine: 195-400 ng/mL
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Wille SM, Cooreman SG, Neels HM, Lambert WE: Relevant issues in the monitoring and toxicology of antidepressants. Crit Rev Clin Lab Sci 2008;45(1):25-89
2. Baumann P, Hiemke G, Ulricj S, et al: The AGNP-TDM expert group consensus guidelines: therapeutic drug monitoring in psychiatry. Pharmacopsychiatry 2004;37:243-265