title: Myeloperoxidase as a generator of drug free radicals.
abstract: Reactive metabolites are believed to be responsible for many types of toxicity, including idiosyncratic drug reactions. Bone marrow is a frequent target of idiosyncratic reactions, and, since these reactions have characteristics that suggest involvement of the immune system, the formation of reactive metabolites by leucocytes could also play a role in the aetiology of idiosyncratic drug reactions. The major oxidation system in neutrophils and monocytes is a combination of NADPH oxidase and myeloperoxidase. This system oxidizes primary arylamines, such as sulphonamides, to reactive metabolites and these drugs are also associated with a high incidence of agranulocytosis, generalized idiosyncratic reactions and/ or drug-induced lupus. Clozapine is oxidized by this system to a relatively stable nitrenium ion; clozapine is also associated with a high incidence of agranulocytosis. Arylamines that have an oxygen or nitrogen in the para position, such as amodiaquine, vesnarinone and 5-aminosalicylic acid, are oxidized to quinone-like reactive intermediates. Aminopyrine is oxidized to a very reactive dication. Such reactive metabolites could also inhibit neutrophil function and mediate some of the therapeutic effects of these drugs: for example, the use of dapsone for dermatitis herpetiformis and the use of 5-aminosalicylic acid for inflammatory bowel disease.
authors.affiliation: Faculty of Pharmacy, University of Toronto, Canada.
authors.forename: J P
authors.initials: JP
authors.lastname: Uetrecht
mesh_terms: D005609:Free Radicals; D006801:Humans; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000378:metabolism*; D004364:Pharmaceutical Preparations / Q000737:chemistry / Q000378:metabolism*
chemical_list: D005609:Free Radicals; D004364:Pharmaceutical Preparations; D009195:Peroxidase