greater. The evolutionary development of tortoises, snakes and crocodiles took
place before mammals evolved, and yet they are grouped together in the possible
hope of achieving common pain behavioural factors for “reptiles”. Not surpris-
ingly, very limited information is available (Machin 1999 ;Mosley 2005 ), but the
indications are that most mechanisms involved in pain inception and transmission
are basically similar. This suggeststhat pain, as a mechanism of survival,
developed very early in the evolution of species and has not changed in its
fundamental manifestations in any significant way over the millennia. Thus,
reptiles, amphibia and fish all respond to the same sort of noxious stimuli; they
all exhibit species-specific behaviours in response to either acute or chronic pain
conditions and they also show alleviation in the response to the stimuli in the
presence of analgesic agents proventobeeffectiveinmammals(Bennett 1998 ;
Stevens et al. 2001 ). Like birds, the use of analgesics in these non-mammalian
vertebrates is severely limited by the lack of information on non-overt behaviours
and lack of information on the pharmacokinetics and pharmacodynamics of
analgesics in these species.
4 Analgesic Agents and Their Use in Domestic Animals
4.1 Local Anaesthetics
It seems clear that the molecular genetics of neuronal sodium channels in most species
have been highly conserved. Although minor variations have been identified, the
general structure and function are essentially similar, which is fortunate as the ionic
mechanisms of nerve conduction were initially investigated in molluscs. As the
mechanism of action of local anaesthetics seems to be similar at most sodium
channels, their effectiveness is correspondingly similar in most species. Hence, the
efficacy demonstrated in man, where the action can depend on the anatomical
structure of the nerve and local concentration of the drug, also applies in domestic
species. All commonly used local anaesthetics are aminoamides. They include lig-
nocaine, bupivacaine and mepivacaine, and have been shown to be effective in all
domestic species (Dobromylskyj et al. 2000 ), as have the less generally used agents
such as prilocaine and ropivacaine (Flecknell et al. 1990 ; Markham and Faulds 1996 ).
In addition, most of the routes of application of local anaesthetics in humans
have been used in domestic animals, and their use in pre-emptive analgesia for the
prevention or suppression of sensitisation has been mentioned. Topical administra-
tion in the form of gels or creams has been used for lidocaine and lidocaine/
prilocaine. These agents and routes are mainly utilised in small animals for the
temporary analgesia associated with the placing of needles or cannulae (Flecknell
et al. 1990 ). Local infiltration by injection of a 1 or 2% w/v solution of lidocaine,
usually with added adrenaline to prolong action by vasoconstriction, is widely used
in most domestic species for superficial or regional blocks. For most veterinary
174 A. Livingston