Patients with chronic pain on opioid therapy taking dronabinol: incidence of false negatives using radioimmunoassay.
BACKGROUND
Serum blood toxicology screens are believed to be important to monitor compliance and to identify levels of illicit substances in patients taking opioids for their chronic pain.


METHODS
In this study, the authors examine the incidence of tetrahydrocannabinol (THC) in consecutive blood samples of patients given dronabinol. We assessed the incidence of THC in 27 patients who participated in a single-dose, double-blind crossover trial of dronabinol (Marinol capsules), a synthetic Delta9-THC, as part of a larger study, to determine the reliability of the toxicology screening. Subjects were randomly administered 10 mg or 20 mg of dronabinol or placebo over the course of three 8-hour visits for a combined 228 serum blood samples. Levels of THC were quantified using radioimmunoassay.


RESULTS
The majority of the samples (57.4 percent) showed presence of study drug as expected. However, 43 samples (42.6 percent) showed no detectable evidence of THC 4 and 8 hours after administration of dronabinol. Five subjects showed lower serum levels on the higher dose (20 mg) than on the lower dose (10 mg) after 4 hours, and two subjects showed lower levels with the higher dose after 8 hours. One subject had no detectable THC on any dose of dronabinol.


CONCLUSIONS
These toxicology reports point to higher than anticipatedfalse-negative results with radioimmunoassay blood serum screening. Results could be explained by the lower sensitivity of this screening technique and also in how oral cannabinoids are metabolized. Further investigations are needed on the accuracy of the detection of THC among patients known to have used dronabinol.
Narang
Sanjeet
S
Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Wasan
Ajay D
AD
Ross
Edgar L
EL
Michna
Edward
E
Chen
Jui-Yuan
JY
Jamison
Robert N
RN
D000328:Adult; D000368:Aged; D000701:Analgesics, Opioid / Q000627:therapeutic use*; D002908:Chronic Disease; D018592:Cross-Over Studies; D004311:Double-Blind Method; D013759:Dronabinol / Q000097:blood* / Q000378:metabolism*; D005188:False Negative Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000188:drug therapy*; D010349:Patient Compliance; D011863:Radioimmunoassay
D000701:Analgesics, Opioid; D013759:Dronabinol