title: Comparative metabolism as a key driver of wildlife species sensitivity to human and veterinary pharmaceuticals.
abstract: Human and veterinary drug development addresses absorption, distribution, metabolism, elimination and toxicology (ADMET) of the Active Pharmaceutical Ingredient (API) in the target species. Metabolism is an important factor in controlling circulating plasma and target tissue API concentrations and in generating metabolites which are more easily eliminated in bile, faeces and urine. The essential purpose of xenobiotic metabolism is to convert lipid-soluble, non-polar and non-excretable chemicals into water soluble, polar molecules that are readily excreted. Xenobiotic metabolism is classified into Phase I enzymatic reactions (which add or expose reactive functional groups on xenobiotic molecules), Phase II reactions (resulting in xenobiotic conjugation with large water-soluble, polar molecules) and Phase III cellular efflux transport processes. The human-fish plasma model provides a useful approach to understanding the pharmacokinetics of APIs (e.g. diclofenac, ibuprofen and propranolol) in freshwater fish, where gill and liver metabolism of APIs have been shown to be of importance. By contrast, wildlife species with low metabolic competency may exhibit zero-order metabolic (pharmacokinetic) profiles and thus high API toxicity, as in the case of diclofenac and the dramatic decline of vulture populations across the Indian subcontinent. A similar threat looms for African Cape Griffon vultures exposed to ketoprofen and meloxicam, recent studies indicating toxicity relates to zero-order metabolism (suggesting P450 Phase I enzyme system or Phase II glucuronidation deficiencies). While all aspects of ADMET are important in toxicity evaluations, these observations demonstrate the importance of methods for predicting API comparative metabolism as a central part of environmental risk assessment.
authors.affiliation: School of Biological Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK tom.hutchinson@plymouth.ac.uk.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Hutchinson
authors.affiliation: School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK.
authors.forename: Judith C
authors.initials: JC
authors.lastname: Madden
authors.affiliation: Departmental of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, Gauteng 0110, South Africa.
authors.forename: Vinny
authors.initials: V
authors.lastname: Naidoo
authors.affiliation: Cissbury, Hillhead, Colyton EX24 6NJ, UK.
authors.forename: Colin H
authors.initials: CH
authors.lastname: Walker
mesh_terms: D000818:Animals; D000835:Animals, Wild / Q000378:metabolism*; D004785:Environmental Pollutants / Q000493:pharmacokinetics* / Q000633:toxicity*; D006801:Humans; D013045:Species Specificity; D019155:Veterinary Drugs / Q000493:pharmacokinetics* / Q000633:toxicity*
chemical_list: D004785:Environmental Pollutants; D019155:Veterinary Drugs
keywords: birds; environment; exposure; fish; invertebrates; medicines