My son is a junior in college on a full athletic scholarship. He also suffers from depression and has recently been prescribed EffexorER. During a routine drug (urine)sreening he was informed of a positive reading for PCP. His character came into question and he could have lost his scholarship. After sending the specimen to a certified lab he was cleared. Meanwhile...
My son is a junior in college on a full athletic scholarship. He also suffers from depression and has recently been prescribed EffexorER. During a routine drug (urine)sreening he was informed of a positive reading for PCP. His character came into question and he could have lost his scholarship. After sending the specimen to a certified lab he was cleared. Meanwhile all doctors and phamarcist we spoke with denied any possibility a false positive reading with this drug.
I hope his scholarship was reinstated.
I suggest in this case you should have a claim for defamation.
I believe this process is taken too lightly by the Schools/Company’s and enforcers they require to be held accountable when they get it wrong.
Salvador F. Sena1a, Syed Kazimi1 and Alan H.B. Wu2
1 Department of Pathology, and Laboratory Medicine, Danbury Hospital, Danbury, CT 06810;2 Department of Pathology, and Laboratory Medicine, Hartford Hospital, Hartford, CT 06102
aAuthor for correspondence....
aAuthor for correspondence. Fax 203-731-8678; e-mail firstname.lastname@example.org
To the Editor:
We recently observed three occurrences of false-positive results for phencyclidine (PCP) on urine samples tested with the Syva® RapidTest d.a.u.® 9 Test Panel (Syva Company, subsidiary of Dade Behring Inc.). The RapidTest d.a.u. 9 device is a single-use, one-step, solid-phase immunochromatographic assay for the qualitative, discrete detection of several drugs/drug metabolites in human urine (1). The urine samples were collected from three different patients who were seen in our Emergency Department within 3-4 weeks after we had implemented the RapidTest device in our laboratory (Danbury Hospital). Because PCP is not a commonly used drug in our locale and the rare positive results have usually been confirmed as false positives, three positive PCP results in such a short time period immediately aroused suspicion.
Patient A was a 52-year-old male with schizoaffective disorder who was admitted to the psychiatry service. Patient B was a 93-year-old female from a nursing home who was admitted with a hip fracture. Patient C was a 50-year-old female admitted for opiate and benzodiazepine overdose. None of these patients had a history of PCP use or presented with symptoms consistent with use of this drug.
Patient A's urine gave negative results for all other drugs tested with the RapidTest. Patient B's urine also tested positive for benzodiazepines and barbiturates; these results could be attributed to medications documented in this patient's medical record: lorazepam, clonazepam, and phenytoin (the latter is listed in the RapidTest package insert as an interferent in the barbiturates assay). Patient C's urine also tested positive for benzodiazepines and opiates; again, these results were consistent with this patient's known medications (lorazepam and hydrocodone). None of the patients was receiving dextromethorphan, diphenhydramine, ibuprofen, imipramine, meperidine, mesoridazine, or thioridazine-drugs known to produce false-positive results with other PCP immunoassays. The only drug that appeared on the medication lists of all three patients was venlafaxine, a relatively new antidepressant marketed as Effexor® (Wyeth-Ayerst Pharmaceuticals, Inc.) (2). We therefore suspected that this drug and/or one or more of its metabolites were the cause of these false-positive results via cross-reactivity with the anti-PCP antibodies used in the RapidTest devices (cutoff concentration for PCP, 25 µg/L).
Negative results were obtained when the same urine samples from these three patients were tested with the Syva Emit II Plus PCP assay (25 µg/L cutoff) on the Roche Cobas MIRA analyzer (performed at Danbury Hospital). Similarly, analysis by two other single-use immunochromatographic devices, OnTrak TesTstik PCP (Roche Diagnostics) and Biosite Triage 8 DOA (Biosite Diagnostics) also gave negative results for PCP (both 25 µg/L cutoff; performed at Hartford Hospital), and gas chromatographic-mass spectrometric analysis did not detect PCP (5 µg/L limit of detection; performed at Hartford Hospital). Of note, we also encountered a "true-positive" PCP sample from an 18-year-old male patient admitted with head trauma; this urine tested positive for PCP by the RapidTest, Emit, and gas chromatographic-mass spectrometric methods and thus served as a "positive control".
Venlafaxine undergoes both O- and N-demethylation, with the major metabolite, O-desmethylvenlafaxine (ODV), also exhibiting antidepressant activity. An average of 87% of a labeled oral dose is excreted in a 48-h urine, with 5% excreted as parent drug, 29-48% as ODV, 6-19% as di-N-desmethylvenlafaxine, and 0.2-7.4% as mono-N-desmethylvenlafaxine (2). To further test our hypothesis that venlafaxine and/or its metabolites were responsible for these false-positive results, we obtained pure samples of venlafaxine and the ODV metabolite from Wyeth-Ayerst Research, the manufacturer of this drug. We prepared solutions of venlafaxine and ODV in drug-free urine at final concentrations of 106, 105, 104, 103, and 102 µg/L venlafaxine or ODV and tested these solutions with both the Emit II and RapidTest PCP assays. The RapidTest gave a clearly positive PCP result (no signal line indicates positive result) at a concentration of 106 µg/L of either venlafaxine or ODV and equivocal or borderline results (extremely faint, barely visible line) at 105 µg/L of either venlafaxine or ODV, whereas the Emit II assay gave negative results at all concentrations. Additional testing narrowed the concentration where the RapidTest became clearly positive for PCP to somewhere between 1 x 105 and 2 x 105 µg/L of either venlafaxine or ODV, indicating similar cross-reactivities for these two compounds. From these data, we calculated a cross-reactivity of between 0.0125% and 0.025% for both the parent drug and metabolite, using the 50% displacement method described by Miller and Valdes (3). Although at face value this appears to be a very low degree of cross-reactivity, it becomes clinically significant if combined concentrations of venlafaxine and ODV of 1 x 105 µg/L are present in a urine sample.
According to the literature, predicted steady-state plasma concentrations of venlafaxine and ODV in healthy individuals receiving daily 150-mg doses are estimated as 70 and 254 µg/L, respectively (2). These concentrations are approximately three orders of magnitude lower than those that were found to give positive results in our addition experiments. Although we could find no published data on urine concentrations of venlafaxine and ODV, we learned that combined concentrations of these two substances on the order of 1 x 105 µg/L have indeed been measured in the urine of patients taking therapeutic doses of venlafaxine (K-T. J. Yeo, personal communication). Combined with the results of our addition experiments, this provides strong evidence that the false-positive results we observed were caused by cross-reactivity of venlafaxine and ODV with the RapidTest PCP assay.
Venlafaxine, designated (R/S)-1-[2-(dimethylamino)-1-(4-methoxyphenyl)ethyl] cyclohexanol, is a phenethylamine derivative that is chemically unrelated to tricyclic, tetracyclic, and other antidepressants. It is the first antidepressant in a new drug class referred to as the serotonin noradrenergic reuptake inhibitors (SNaRIs) (4). Aside from possessing phenyl and cyclohexyl groups, venlafaxine bears little structural similarity to phencyclidine [1-(1-phenylcyclohexyl)piperidine; see Fig. 1 ]. Given this structural dissimilarity, it is somewhat surprising that venlafaxine or any of its desmethyl metabolites would cross-react with the anti-PCP antibody used in the RapidTest device. However, other examples of unexpected interferences with immunoassays for drugs of abuse have been well documented in the literature, e.g., oxaprozin with the Emit assay for benzodiazepines (5) and efavirenz with the CEDIA test for cannabinoids (6)(7).
There are also reports in the literature of urine screen false positives for PCP occurring with diphenhydramine, found in Benadryl, Tylenol PM, and many other nonprescription medicines. A similar antihistamine, doxylamine (Unisom and other brands) has also caused false positives on gas chromatography.
I also tested positive for PCP. Never seen it, don't know how to "do it". I am also on Effexor XR. What is going on? I was tested a few months back and it was negative yet I was on Effexor XR at that time also. Same dose. If anyone knows anything, please share. I checked with my counties drug and alcohol rehabilitation and counseling service. They neveer...
I also tested positive for PCP. Never seen it, don't know how to "do it". I am also on Effexor XR. What is going on? I was tested a few months back and it was negative yet I was on Effexor XR at that time also. Same dose. If anyone knows anything, please share. I checked with my counties drug and alcohol rehabilitation and counseling service. They neveer had the problem. So many people take effexor! No one seeking drug/alcohol help is on medication for depression? Highly unlikely. What is with inconsistancy and why isn't everyone testing positive that takes Effexor.
The new anti-depressant Pristiq (desvenlafaxine; Effexor is venlafaxine) can also cause a false positive reaction to PCP. This occurred with a patient in my practice just today in fact.
I am on Effexor XR, aspirin, hydroxyurea (for thrombocytosis), and Nasonex. I have a history of drug abuse but have been clean for almost 9 months now. I tested positive twice for PCP and now am in alot of trouble with the court system due to being on probation. I truly have not used PCP at all (my drug of choice was opiates) and I am trying...
I am on Effexor XR, aspirin, hydroxyurea (for thrombocytosis), and Nasonex. I have a history of drug abuse but have been clean for almost 9 months now. I tested positive twice for PCP and now am in alot of trouble with the court system due to being on probation. I truly have not used PCP at all (my drug of choice was opiates) and I am trying to find out where I can get accurate information on this to show the courts. I have worked so hard to stay clean and to now test postive twice for PCP (via mouth swab) is absolutely devastating! Please if anyone has information, especially a medical professional, I would appreciate it. Thank you
I just took an onsight urine drug screen and it came up positive for PCP and amphetamines. I do not do either of these things. I take the following medications and was wondering if any of them could possibly do such a thing. Effexor XR, Seroqel and Anafrinil.
Hi MD Nelson,
I need to know what is Effexor half-life and detection time. I'm extremely well informed on neurotransmitters and hormones, so, consider you talk to someone who will understand your answer thoroughly.
This is urgent for me to have an answer.
Thank you very much
I'm fighting with my doctor because of effexor, i tested positive for pcp, i do not do drugs, my doctor threw me out of her office and told me she knew i was on drugs. Now i have to go on line and tell the hospital what test to use. YOU ARE A CARING DOCTOR, UNFORTUNATELY MINES NOT