title: Immune-mediated agranulocytosis caused by the cocaine adulterant levamisole: a case for reactive metabolite(s) involvement.
abstract: The United States Public Health Service Administration is alerting medical professionals that a substantial percentage of cocaine imported into the United States is adulterated with levamisole, a veterinary pharmaceutical that can cause blood cell disorders such as severe neutropenia and agranulocytosis. Levamisole was previously approved in combination with fluorouracil for the treatment of colon cancer; however, the drug was withdrawn from the U.S. market in 2000 because of the frequent occurrence of agranulocytosis. The detection of autoantibodies such as antithrombin (lupus anticoagulant) and an increased risk of agranulocytosis in patients carrying the human leukocyte antigen B27 genotype suggest that toxicity is immune-mediated. In this perspective, we provide an historical account of the levamisole/cocaine story as it first surfaced in 2008, including a succinct review of levamisole pharmacology, pharmacokinetics, and preclinical/clinical evidence for levamisole-induced agranulocytosis. Based on the available information on levamisole metabolism in humans, we propose that reactive metabolite formation is the rate-limiting step in the etiology of agranulocytosis associated with levamisole, in a manner similar to other drugs (e.g., propylthiouracil, methimazole, captopril, etc.) associated with blood dyscrasias. Finally, considering the toxicity associated with levamisole, we propose that the 2,3,5,6-tetrahydroimidazo[2,1-b]thiazole scaffold found in levamisole be categorized as a new structural alert, which is to be avoided in drug design.
authors.affiliation: Pharmacokinetics, Dynamics, and Metabolism Department, Pfizer Worldwide Research and Development, Groton, Connecticut, USA.
authors.forename: Angela
authors.initials: A
authors.lastname: Wolford
authors.forename: Thomas S
authors.initials: TS
authors.lastname: McDonald
authors.forename: Heather
authors.initials: H
authors.lastname: Eng
authors.forename: Steven
authors.initials: S
authors.lastname: Hansel
authors.forename: Yue
authors.initials: Y
authors.lastname: Chen
authors.forename: Jonathan
authors.initials: J
authors.lastname: Bauman
authors.forename: Raman
authors.initials: R
authors.lastname: Sharma
authors.forename: Amit S
authors.initials: AS
authors.lastname: Kalgutkar
mesh_terms: D000380:Agranulocytosis / Q000139:chemically induced* / Q000276:immunology* / Q000378:metabolism*; D000818:Animals; D003042:Cocaine / Q000737:chemistry / Q000378:metabolism* / Q000506:poisoning; D004340:Drug Contamination; D006801:Humans; D007978:Levamisole / Q000737:chemistry / Q000378:metabolism* / Q000506:poisoning; D014481:United States; D014492:United States Public Health Service / Q000331:legislation & jurisprudence; D019155:Veterinary Drugs / Q000737:chemistry / Q000378:metabolism / Q000506:poisoning
chemical_list: D019155:Veterinary Drugs; D007978:Levamisole; D003042:Cocaine