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effexor can cause a false/positive pcp result

Posted by Jaynee on January 20, 2004, at 21:13:47

In reply to Re: Effexor Dangerous? Ask Andrea Yates? » oracle, posted by shelye on January 18, 2004, at 20:08:28

Journal Article | Print Published: 12/31/2003 | Online Published: 12/03/2003
Pages: 999 - 1002 | PDF File Size: 55 KB
DOI: 10.1081/CLT-120026525


Venlafaxine, Phencyclidine, Urine drug screen, Abbott AxSYM® immunoassay


Case report: A 13-yr-old girl overdosed on 48 × 150 mg venlafaxine (Effexor XR®). She was taking venlafaxine regularly for depression. Her only other medications included topical Benzamycin and pyridoxine 50 mg daily for acne. The Abbott AxSYM® assay was positive only for phencyclidine, but GC/MS did not confirm the presence of phencyclidine. Toxilab® identified only one substance, confirmed by GC/MS as venlafaxine. A serum sample obtained 3 h after her ingestion revealed a venlafaxine concentration of 24460 ng/mL and an O-desmethylvenlafaxine concentration of 3930 ng/mL, confirming the massive acute overdose (therapeutic range of venlafaxine and O-desmethylvenlafaxine together is 250–750 ng/mL). Urine spiked with 4.2 mg/mL of venlafaxine and 0.7 mg/mL of O-desmethylvenlafaxine was interpreted as positive with the Abbott AxSYM® fluorescent polarized immunoassay for phencyclidine (readout of 28 ng/mL). Conclusion: Venlafaxine may cause a false positive Abbott AxSYM® phencyclidine assay when present in very high concentrations. Physicians should be aware of this potential reaction when interpreting urine drug immunoassays.




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