title: Pyrilamine and O-desmethylpyrilamine detection in equine serum and urine.
abstract: Pyrilamine (mepyramine) is an H1-receptor antagonist used in human and veterinary medicine. It has the potential to produce central nervous system effects in horses and therefore may have some impact on an outcome of a horse race. A single oral dose of pyrilamine (300 mg/horse) was given to three animals. Serum samples were collected before drug administration and at 0.25, 0.5, 1, 2, 4, 6, 24, 48, 72, 96, 120, and 144 h, and 7, 8, 9, 10, 11, 12, and 13 days post-administration. Urine samples were collected at 0-1, 1-2, 2-4, 4-6, 24, 48, 72, 96, 120, and 144 h, and 7, 8, 9, 10, 11, 12, 13 days post-administration. Urine and serum samples were initially screened by the pyrilamine enzyme-linked immunosorbent assay (ELISA) kit with subsequent confirmation and quantitation utilizing a newly developed and validated gas chromatography-mass spectrometry (GC-MS) method for pyrilamine and its major metabolite O-desmethylpyrilamine with chlorpromazine as an internal standard. Prior to the basic extraction, urine specimens were hydrolyzed using beta-glucuronidase. The urine extracts as well as the serum samples were then subjected to solid-phase extraction on Bond Elut LRC-PRS columns. Pyrilamine was not found in any of the urine samples but it was present in serum in low concentrations (4-123 ng/mL) up to 6 h after drug administration. The limit of detection and limit of quantitation for the GC-MS method for pyrilamine in serum were 1.5 and 3.1 ng/mL, respectively, and for O-desmethylpyrilamine in urine were 5 and 6.2 ng/mL, respectively. Pyrilamine concentration in serum peaked at 15 min, 30 min, and 1 h in horse #1, #2, and #3, respectively. Urine specimens were screened positive for pyrilamine and its metabolites using ELISA for extended periods of time (4 days in one horse and 9 days in two other animals). Using GC-MS, O-desmethylpyrilamine was detected in urine for 11 days in horse #1, 4 days in horse #2, and 9 days in horse #3. While pyrilamine was eliminated from the bloodstream rather quickly, the metabolite level remained in the urine for days after administration. When evaluating laboratory results, regulators must take into account that a urine sample positive for O-desmethylpyrilamine does not necessarily indicate that the drug remains active in the horse's system, possibly affecting the outcome from the race.
authors.affiliation: Animal Forensic Toxicology Laboratory, University of Illinois at Chicago, 2242 West Harrison Street, Chicago, Ilinois 60612, USA.
authors.forename: Marc
authors.initials: M
authors.lastname: Benoit
authors.forename: Kelly
authors.initials: K
authors.lastname: Lingen
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Taddei
authors.forename: Brendan T
authors.initials: BT
authors.lastname: Heffron
authors.forename: Laura
authors.initials: L
authors.lastname: Hurt
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Lokanc
authors.forename: Katherine
authors.initials: K
authors.lastname: Lingner
authors.forename: Esau
authors.initials: E
authors.lastname: Cardenas
authors.forename: Salvador
authors.initials: S
authors.lastname: Flores
authors.forename: David
authors.initials: D
authors.lastname: Mayer
authors.forename: Donna
authors.initials: D
authors.lastname: Pilipiak
authors.forename: Dawn
authors.initials: D
authors.lastname: Folker-Calderon
authors.forename: Adam
authors.initials: A
authors.lastname: Negrusz
mesh_terms: D000818:Animals; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006634:Histamine H1 Antagonists / Q000032:analysis*; D006736:Horses; D006801:Humans; D011738:Pyrilamine / Q000031:analogs & derivatives* / Q000032:analysis* / Q000097:blood / Q000652:urine
chemical_list: D006634:Histamine H1 Antagonists; C533317:O-desmethylpyrilamine; D011738:Pyrilamine