Plasma Disposition, Faecal Excretion, Metabolism and Chirality of Anthelmintic Drugs in Horses
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PLASMA DISPOSITION, FAECAL EXCRETION, METABOLISM AND CHIRALITY OF ANTHELMINTIC DRUGS IN HORSES A thesis submitted for the degree of Doctor of Philosophy by Cengiz Gokbulut, DVM. Department of Veterinary Preclinical Studies Division of Veterinary Pharmacology, University of Glasgow October 2000 © C. GOKBULUT, 2000 ProQuest Number: 13818965 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 13818965 Published by ProQuest LLC(2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 GLASGOW UNIVERSITY LIBRARY * II95A " C o \ To my wife, Nurgul and my little daughter, Elif i CONTENTS Contents .................................................................................................................... i Acknowledgements ................................................................................................. v Declaration ............................................................................................................... vi Summary .................................................................................................................. vii Abbreviations ......................................................................................................... x CHAPTER 1: GENERAL INTRODUCTION.................................................. 1 1.1 INTERNAL PARASITE INFECTIONS IN HORSES.................................... 2 1.2 ANTHELMINTICS IN HORSES..................................................................... 4 1.2.1 BENZIMIDAZOLES IN HORSES.............................................................. 4 1.2.1.1 Chemistry and Metabolism ......................................................................... 4 1.2.1.2 Efficacy and Spectra of Activity ................................................................. 8 1.2.1.3 Mode of Action ............................................................................................ 8 1.2.1.4 Safety and Toxicity ..................................................................................... 10 1.2.1.5 Pharmacokinetics ......................................................................................... 11 1.2.1.6 Chirality of Benzimidazoles ....................................................................... 17 1.2.2 AVERMECTINS AND MILBEMYCINS IN HORSES ............. 18 1.2.2.1 Chemistry and Metabolism ....................................................... 19 1.2.2.2 Efficacy and Spectra of Activity ............................................................... 22 1.2.2.3 Mode of Action ............................................................................................ 23 1.2.2.4 Safety and Toxicity ....................................................... 25 1.2.2.5 Pharmacokinetics ......................................................................................... 26 1.2.3 PYRANTEL IN HORSES..................... 32 1.2.3.1 Chemistry and Metabolism ......................................................................... 32 1.2.3.2 Efficacy and Spectra of Activity ................................................................. 33 1.2.3.3 Mode of Action ............................................................................................ 33 1.2.3.4 Safety and Toxicity ..................................................................................... 33 1.2.3.5 Pharmacokinetics ......................................................................................... 34 1.3 ANTHELMINTIC RESISTANCE IN HORSES.......................................... 35 1.4. STUDY OBJECTIVES.................................................................................... 37 CHAPTER 2: PHARMACOKINETICS, METABOLISM AND CHIRALITY OF BENZIMIDAZOLES IN HORSES.................................... 38 11 Section 1. Pharmacokinetics and faecal excretion pattern of oxfendazole, fenbendazole and oxibendazole inhorses ............................................................ ^ 2.1.1 Introduction ...................................................................................................... 39 2.1.2 Materials and methods .................................................................................... 41 2.1.2.1 Animals ......................................................................................................... 41 2.1.2.2 Drug administration and sampling procedure ............................................ 41 2.1.2.3 Drug analysis ................................................................................................ 43 2.1.2.3.1 Standard preparation ................................................................................. 43 2.1.2.3.2 Extraction from plasma ............................................................................ 43 2.1.2.3.3 Extraction from faeces ............................................................................. 44 2.1.2.3.4 HPLC system............................................................................................. 44 2.1.2.3.5 Recovery and precision ............................................................................ 45 2.1.2.3.6 Pharmacokinetic and statistical analysis of data ..................................... 45 2.1.2.4 Chiral analysis ............................................................................................ 47 2.1.3 Results .............................................................................................................. 49 2.1.4 Discussion ........................................................................................................ 67 Section 2. Effect of piperonyl butoxide on the pharmacokinetics and chirality of oxfendazole in ponies; in vivo study............................................ ^ 2.2.1 Introduction ...................................................................................................... 70 2.2.2 Materials and methods .................................................................................... 71 2.2.2.1 Animals ......................................................................................................... 71 2.22.2 Experimental design ..................................................................................... 71 2.2.2.3 Drug administration and sampling procedure ............................................ 72 2.2.2.4 Drug analysis ................................................................................................ 72 2.22.5 Chiral analysis ............................................................................................ 72 2.2.3 Results .............................................................................................................. 72 2.2.4 Discussion ........................................................................................................ 85 Section 3: Effect of piperonyl butoxide on the metabolism and chirality of benzimidazoles in microsome samples of equine liver: in vitro study ^ 2.3.1 Introduction ...................................................................................................... 87 2.3.2 Materials and methods .................................................................................... 87 2.3.2.1 Liver microsome preparation ...................................................................... 87 2.3.2.1.1 Chemicals.................................................................................................. 87 iii 2.3.2.1.2 Isolation of microsomes ........................................................................... 88 2.3.2.1.3 Drug incubation ......................................................................................... 89 2.3.2.2 Drug analysis ............................................................................................... 89 2.3.2.2.1 Extraction .................................................................................................. 89 2.3.2.2.2HPLC system............................................................................................ 89 2.3.2.2.3 Statistic analysis of data ........................................................................... 90 2.3.3 Results .............................................................................................................. 90 2.3.4 Discussion .......................................................................................................... 100 CHAPTER 3: PHARMACOKINETICS AND FAECAL EXCRETION PATTERN OF AVERMECTINS AND MILBEMYCINS IN HORSES 102 3.1 Introduction ........................................................................................................... 103 3.2 Materials and methods ......................................................................................... 103 3.2.1 Animals .............................................................................................................. 103 3.2.2 Drug administration and sampling procedure ................................................. 104 3.2.3 Drug analysis ....................................................................................................