To characterize the demographic, clinical, and epidemiologic features of levamisole-associated neutropenia in cocaine or heroin users.

State health departments were recruited for participation when the Centers for Disease Control and Prevention (CDC) was notified of potential cases by a clinician, a health department official, or a poison center between October 15, 2009, and May 31, 2010. A case was defined as a person with an absolute neutrophil count less than 1,000 cells/μL (or a WBC count <2,000 cells/μL) and a self-reported history or laboratory confirmation of cocaine or heroin use. Health department officials abstracted data from medical charts, attempted a patient interview, and submitted data to CDC for descriptive analysis.

Of the 46 potential cases reported from 6 states, half met eligibility criteria and had medical chart abstractions completed (n=23; 50%). Of these, close to half of the patients were interviewed (n=10; 43%). The average age was 44.4 years; just over half were men (n=12; 52%). The majority of patients presented to emergency departments (n=19; 83%). More than half presented with infectious illnesses (n=12; 52%), and nearly half reported active skin lesions (n=10; 44%). The majority of interview respondents used cocaine greater than 2 to 3 times a week (n=9; 90%), used cocaine more than 2 years (n=6; 60%), and preferred crack cocaine (n=6; 60%). All were unaware of exposure to levamisole through cocaine and of levamisole's inherent toxicity (n=10; 100%).

Physicians should suspect levamisole exposure in patients using illicit drugs, cocaine in particular, who present with unexplained neutropenia. Most patients reported chronic cocaine use and were unaware of levamisole exposure. Cocaine use is more prevalent among men; however, our results identified a higher-than-expected proportion of female users with neutropenia, suggesting women may be at higher risk. Emergency physicians and practitioners are uniquely positioned to recognize these patients early during their hospital course, elucidate a history of cocaine or other drug exposure, and optimize the likelihood of confirming exposure by arranging for appropriate drug testing.