to the editor: A 24-year-old man presented to the emergency department with a fever, sore throat, and a lingering productive cough for the past month. He also had experienced myalgias and shortness of breath, and noticed he had sores in his mouth and throat for two days. He denied any recent travel or exposure to anyone with tuberculosis.

Physical examination revealed a temperature of 102.5°F (39.2°C) and an apparent left-sided peritonsillar abscess that was confirmed on head computed tomography (see accompanying figure). The patient was leukopenic (white blood cell count of 2,100 cells per mm³ [2.1 × 10⁹ per L]) with an absolute neutrophil count of zero. His urine drug screening was positive for cocaine, opiates, and cannabinoids. The cause of the neutropenia was determined to be levamisole, a common contaminant in cocaine. The patient eventually admitted to heavy crack cocaine use. The abscess was drained and he was discharged on intravenous antibiotics in stable condition five days later.

Approximately 2 million Americans use cocaine each month.¹ Cocaine contaminated with levamisole has been reported in North America and Europe since 2004.² As of July 2009, levamisole contaminated at least 70 percent of the cocaine that came into the United States and was seized by the U.S. Drug Enforcement Administration.³

Levamisole is a veterinary antihelminthic previously used as an immunomodulator in rheumatoid arthritis, and as adjuvant therapy in the treatment of colorectal cancer. It is no longer available in North America for human use; it is still available in the United States and South America for veterinary administration.⁴ Up to 20 percent of users develop agranulocytosis.⁵ This adverse effect appears to be caused by an autoimmune response, but the exact mechanism is unknown.^4–6 Once patients become neutropenic, they are at risk of opportunistic infections. The likelihood of finding levamisole in blood or urine decreases markedly after 48 hours of use because of its short half-life of approximately five hours.³ The effect of levamisole on cocaine is unknown, but it has been speculated that it may increase the drug's psychoactive effects.^1,4–6

We recommend that patients who use cocaine and develop signs of infection have a complete blood count to evaluate for neutropenia. In addition, levamisole-tainted cocaine use should be considered in the differential diagnosis of patients with unexplained agranulocytosis.