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SAUNDERS
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First published 2004
Reprinted 2004, 2005
ISBN 0 7020 2484 8
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Note
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must be followed, but as new research and clinical experience broaden our
knowledge, changes in treatment and drug therapy may become necessary
or appropriate. Readers are advised to check the most current product
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Contributors
Joseph J. Bertone
DVM MS Diplomate ACVIM
Professor of Equine Medicine, Western University of Health
Sciences, Pomona, CA, USA
I. Mark Bowen
BvetMed Cert VA Cert EM (IntMed) MRCVS
Royal Veterinary College, University of London, UK
Michel Levy
DVM Diplomate ACVIM
Purdue University, School of Veterinary Medicine,
West Lafayette, IN, USA
Sandy Love
BVMS PhD MRCVS
Department of Veterinary Clinical Studies,
University of Glasgow, UK
Jennifer M. MacLeay
DVM PhD Diplomate ACVIM
Department of Clinical Sciences, Colorado State University,
Fort Collins, CO, USA
Celia M. Marr
BVMS MVM PhD DEIM Diplomate ECEIM MRCVS
Beaufort Cottage, Equine Hospital, Newmarket, UK
Diane E. Mason
DVM MS PhD Diplomate ACVA
Department of Clinical Sciences, Kansas State University,
Manhattan, USA
Andrew Matthews
BVM&S PhD FRCVS
McKenzie, Bryson and Marshall, Kilmarnock, UK
Michael J. Murray
DVM MS Diplomate ACVIM
Merial Ltd, Duluth, GA, USA
Bonnie R. Rush
DVM MS Diplomate ACVIM
Department of Clinical Science, Kansas State University,
Manhattan, USA
Harold C. Schott II
DVM PhD Diplomate ACVIM
Department of Large Animal Clinical Sciences,
Veterinary Medical Center, Michigan State University,
East Lansing, USA
Janice E. Sojka
VMD MS Diplomate ACVIM
Purdue University, School of Veterinary Medicine,
West Lafayette, IN, USA
Sally Vivrette
DVM PhD Diplomate ACVIM
Triangle Equine Mobile Veterinary Services, Cary, NC, USA
Tom Yarbrough
DVM Diplomate ACVS
School of Veterinary Medicine, University of
California, Davis, USA
Robert M. Christley
BVSc PhD Dipl VCS MVCS Diplomate
ECVPH MRVCS
Department of Veterinary Clinical Science,
University of Liverpool, Neston, South Wirral, UK
Kevin T. T. Corley
BSc BVM&S MS PhD Diplomate ACVIM &
ACVECC MRCVS
Royal Veterinary College, University of London, UK
Laurent Couetil
DVM Diplomate ACVIM
Purdue University, School of Veterinary Medicine,
West Lafayette, IN, USA
Karina COX
BS
KL Maddy Equine Analytical Chemistry Laboratory,
School of Veterinary Medicine, University of California,
Davis, USA
Patricia M. Dowling
DVM MS Diplomate ACVIM & ACVCP
Department of Veterinary Biomedical Sciences
Western College of Veterinary Medicine,
Saskatoon, Canada
Jonathan Elliott
MA VetMB PhD Cert SAC Diplomate ECVPT
MRCVS
Royal Veterinary College, University of London, UK
Clara K. Fenger
DVM PhD Diplomate ACVIM
Equine Internal Medicine Consulting, Georgetown, KY, USA
Linda J. I. Horspool
BVMS PhD DipECVPT MRCVS
Intervet International, Boxmeer, Netherlands
Cynthia Kollias-Baker
DVM PhD Diplomate ACVCP
Racing Laboratory, College of Veterinary Medicine,
University of Florida, Gainesville, USA
Preface
Equine clinical pharmacology is by definition
'the study of drugs in equine clinical cases'.
Rational drug therapy, founded on pharmacolog-
ical principles, requires a medical diagnosis.
In
fact, without this diagnosis and an understand-
ing of the relevant pathophysiology, knowledge
of pharmacologic principles and specific thera-
peutic objectives, one cannot rationally prescribe
drug therapy.
This first edition of
Equine Clinical Pharmacology
brings together many of the topics pertinent to
daily practice for equine veterinarians. This book
has a number of goals.
It
aims to provide both
veterinarians and veterinary students with a
source of current information about the rational
use of drugs, including best practice principles, in
the treatment of specific diseases in the horse.
Secondly,it aims to provide an incentive for adopt-
ing a rational approach to drug therapy in clinical
cases and in addition to stimulating sustained
interest in the conducting of controlled studies of
the safety and efficacy ofdrugs in diseased horses.
This book has been organized mainly around
bodily systems, since many clinical problems in
horses are related to disorders of one or more of
these systems. The editors have made an effort to
include information on pathophysiology and the
dosage, best practice guidelines, precautions and
potential adverse effects of the drugs discussed.
It
is hoped that this information will help the reader
in making risk/benefit assessments and
in
deter-
mining the therapeutic objectives for each equine
treated.
The contributors to this volume, recognized
experts in their specialties, were selected on the
basis of their particular research and/or clinical
specialization and expertise. Their recommenda-
tions for drug therapy are based on studies
reported in veterinary medical literature, where
possible, and on their own personal experience.
The medications described do not necessarily
have specific approval from the European
Medicines Evaluation Agency, Food and Drugs
Administration or other similar agencies, for the
treatment of the diseases for which they are rec-
ommended. Whilst every effort has been made to
include the most up-to-date recommendations,
information about drug dose rates and dosage
forms is constantly changing. The dose rates
given should generally be considered as averages
or starting points and thus require individual-
ization. Similarly, new drugs that were not
approved at the time of publication may appear
on the market and other drugs or dosage forms
may no longer be available.
This book could not be all-inclusive.
It
is
hoped, however, that it will stimulate the contin-
uation of interest and studies in equine clinical
pharmacology and help better arm the equine
veterinarian for the
therapeutic decisions they
make on a daily basis.
Joseph J. Bertone
Linda J.1. Horspool
Acknowledgements
This 1st Edition of
Equine Clinical Pharmacology
would not have been possible without the gener-
ous support and contributions of many people.
The contributors, selected because each is rec-
ognized as among the most accomplished in
their respective disciplines, provided up-to-date
chapters discussing both modem trends and best
practice principles and managed to adhere to
sometimes apparently impossible deadlines.
This work would of course not exist without the
excellent and well focused contributions of: Mark
Bowen, Rob Christley, Kevin Corley, Laurent
Couetil, Karina Cox, Patricia Dowling, Jonathan
Elliott, Clara Fenger, Cindy Kollias-Baker,
Michael Levy, Sandy Love, Diane Mason, Andy
Matthews, Celia Marr, Michael Murray, [en
MacLeay, Bonnie Rush, Harold Schott II, Janice
Sojka, Sally Vivrette and Tom Yarbrough. A spe-
cial thank you also to Michele Doucet and
Jill
Price for critiquing chapters of the manuscript for
technical content and for providing many benefi-
cial suggestions. The manuscript was greatly
enhanced by their thoughtful attentions. Thanks
also to Joyce Rodenhuis, Samantha Ross and Zoe
Youd at Elsevier Limited for their guidance and
support particularly during the final stages of
preparation of the manuscript and for their
encouragement in getting this project back on
track.
Joseph J Bertone would like to dedicate this
work to Mel and the children, Tina and Carmine,
and to his parents Tina and John.
Linda Horspool would like to express her heart-
felt thanks to her parents Billand Una Horspool for
their continued encouragement and support and
to Marco Franken and his family, Wily,Patricia and
Frank Franken,
Kim
Konings, and Francis and Lola
Kuenen, for their patience and understanding.
She dedicates this work to the memory of Tonny
Franken-Franssen.
CHAPTER CONTENTS
Introduction
1
Basic principles of
veterinary pharmacology
for equine practitioners
Joseph
J.
Bertone
Physicochemical factors in drug
transfer across membranes
2
Absorption 2
Drug administration
3
Distribution
4
Biotransformation
5
Elimination 6
Urinary excretion 6
Gastrointestinal excretion
6
Excretion in milk
6
Pharmacokinetics
7
Clearance
7
INTRODUCTION
Half-life 7
Mean residence time
8
Unfortunately, drugs do not distribute in living
organisms as though injected into balloons filled
with fluid. The study of how drugs react in living
tissues and organisms is pharmacology. The science
of pharmacology includes many different fields.
The relationship between the dose of a drug given
to an animal and the use of that drug in treating
diseases is pharmacokinetics; what the body does
to a drug and what a drug does in the body is
pharmacodynamics, and whether it is desirable or
undesirable
is
toxicology.
Pharmacokinetics is the study of absorption,
distribution, biotransformation (metabolism) and
excretion of drugs. The end result is determined
by the physical, chemical and biochemical prin-
ciples that govern the transfer and distribution of
drugs across biological membranes. These factors
and the dosage (route, dose and frequency) deter-
mine the drug concentration at the site of action
and the intensity of a drug's effects as a function of
time. Pharmacodynamics is the study of the mech-
anisms of action of drugs and their biochemical
and physiological effects. Toxicology is the field of
pharmacology that deals with the adverse effects
of drugs used in therapy and of other non-drug
chemicals.
A drug's usefulness as a therapeutic agent is
critically dependent on its ability to produce desir-
able effects and a tolerable level of undesirable
effects. Therefore, the selectivity of a drug's effects
is one of its most important characteristics. Drug
therapy is based on the correlation of the effects
of drugs with the
Volumes of distribution
8
Bioavailability
10
Other clinically relevant concepts
10
The loading dose 10
Maximum plasma concentration
10
References
10
Suggested reading
11
physiological, biochemical,
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