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HOUSTON -- Half of a group of cocaine users tested positive for levamisole, a potentially hazardous veterinary drug that cocaine dealers often use to prepare street product, investigators reported here.

Preliminary data from an ongoing study showed that 24 of 46 cocaine-positive urine samples also contained the anthelmintic, which has been banned for human use in the United States since 2000.

Four of the 46 cocaine users had evidence of vasculitis, an adverse effect of levamisole, and three of the four also tested positive for the deworming drug.

"The potential public health implications are huge," Jennifer Hong, MD, of Vanderbilt University in Nashville, Tenn., told 名媛直播 during a poster presentation at the Society of Critical Care Medicine meeting.

"Levamisole can be highly toxic in humans, but unless you're specifically looking for it in a urine sample, you won't know it's there. Physicians who treat cocaine users need to be aware of this because most users probably wouldn't care, even if they knew the drug was contaminated with levamisole."

Although not available for human use, levamisole remains widely used in veterinary medicine for treating worms in livestock and domesticated animals. The drug can cause agranulocytosis, as well as vasculitis, which prompted the FDA ban on human use.

Drug dealers have long used levamisole in preparing bulk product for street sales. In late 2009 the CDC confirmed a link between levamisole-tainted cocaine and almost two dozen cases of agranulocytosis among users.

Despite the hazards, levamisole use in the illicit drug trade remains widespread. The U.S. Drug Enforcement Agency reported last year that more than 80% of cocaine seized by law enforcement officials contained levamisole. In humans, the drug is thought to bind to the same receptors as cocaine does, thereby enhancing the euphoric effects.

A case report published last year provided details of a half dozen cocaine users who developed severe vasculitis and neutropenia as a result of levamisole exposure (J Am Acad Derm 2011; 65: 722-725).

Given the history of levamisole-contaminated cocaine, Hong and colleagues examined the issue at their center, reviewing records on urine samples submitted for drug screening from January 2009 to March 2010. They identified 46 specimens that tested positive for the cocaine metabolite benzoylecgonine (BEG).

Investigators reanalyzed those specimens by gas chromatography/mass spectometry, including screens for cocaine, BEG and other cocaine metabolites, as well as certain contaminants, such as levamisole.

Hong reported that 52% of the cocaine-positive urine samples contained levamisole, and none of the patients had a prescription for the anthelmintic. In addition to the four patients with vasculitis, four others had tachydysrhythmias, three of whom tested positive for levamisole.

Of 24 patients with results from complete blood count analysis, one had evidence of neutropenia.

Exploration of the cocaine-levamisol toxicity link will continue, said Hong. Their team hopes to study the issue prospectively to learn more about the presence of levamisole and other contaminants introduced into cocaine for street sales and about potential health hazards associated with use of tainted cocaine.

"For now I think the best thing that can be done is to make physicians and other healthcare professionals aware of the problems associated with contaminated cocaine and keep them in mind when treating patients who use cocaine, especially patients who have symptoms that suggest use of a contaminated drug," said Hong.

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