Pharmacologic management of pain in the equine patient (Proceedings)


Pharmacologic management of pain in the equine patient (Proceedings)

Aug 01, 2008

What is pain?

• "an unpleasant sensory and emotional experience associated with actual or potential tissue damage" (International Association for the Study of Pain)

How is pain evaluated in the equine patient?

• Very Difficult!!!!

• Based mostly on subjective evaluation

• May not be evident until severe

o Example of signs of pain: depression, agitation, anorexia, tachycardia, tachypnea, lameness, colic

Pathway of pain

• First order neurons

o Two types of pain receptors (nociceptors):

• Type Aδ myelinated nerve fibers = first, sharp pain

• Type C non-myelinated nerve fibers = slow, burning pain

• Second order neurons

o Dorsal horn of grey matter

o "Gated"

• Excitatory

• Inhibitory

• Spinothalamic tract

o Major ascending pathway for pain conduction

o Contralateral side

• Ventral white matter

• Third order neurons

o In thalamus

o Project to cortex

What is pain? – There are 2 types:

• Physiologic pain

o Stems from noxious stimuli

o Perception is proportional to intensity of stimuli

o "Protective Pain"

o Stimulates a response

• Pathologic pain

o From tissue damage (e.g. inflammation)

o Perception is greater than stimulus

Goals of pain management

• Reduce the morbidity and mortality in patient.

Methods of pain management

• Drugs – IV, IM, oral

• Epidurals

• Continuous rate infusions

• Transdermal

• Novel approaches


• Inhibit cyclooxygenases (COX)

• Decrease prostaglandin and thromboxane A2

• Effective as analgesics when inflammatory response is present

• Reduce hypersensitivity to pain (local effects)

• May have some central effects (speculated)

• Phenylbutazone

o 2.2 to 4.4 mg/kg BID

o Cumulative affects by 48 hours post-administration

o Oral absorption highly variable especially in fed animal (2-12 hours for peak), but good total absorption

o Peak concentration 3-4 hours (fasted)

o T ½ = 3 - 7 hours (dose dependent)

o Strong COX-1

• Flunixin meglumine

o 1.1 mg/kg