Analgesic Agents- Opioids Flashcards
Define ‘Pain’
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
Define Nociception
Perception of pain or injurious stimuli
-Nociception is the sensory nervous system’s process of encoding noxious stimuli. In nociception, intense chemical (e.g., cayenne powder), mechanical (e.g., cutting, crushing), or thermal (heat and cold) stimulation of sensory nerve cells called nociceptors produces a signal that travels along a chain of nerve fibers via the spinal cord to the brain. Nociception triggers a variety of physiological and behavioral responses and usually results in a subjective experience, or perception, of pain in sentient beings.
Define Allodynia
a condition where pain is caused by a stimulus that does not normally elicit pain. For example, bad sunburn can cause temporary allodynia, and touching sunburned skin, or running cold or warm water over sunburned skin can be very painful.
Define Hyperalgesia
Increased sensitivity to pain
Define Neuropathic Pain
Neuropathic pain is pain caused by damage or disease affecting the somatosensory nervous system
Define Central Sensitization
Central sensitization is a condition of the nervous system that is associated with the development and maintenance of chronic pain.
When an animal is repeatedly exposed to a painful stimulus, the animal’s pain threshold will change and result in a stronger pain RESPONSE
Define Analgesia
The reduction in the intensity of pain perceived
What are the 4 compartments of the pain pathway that can be targeted for pain management?
Transduction (PNS)
Transmission (PNS)
Modulation (CNS)
Perception (CNS)
Define an Opiate and an Opioid
Opioids refer to all natural, semisynthetic, and synthetic opioids
Opiates refer to only natural opioids such as heroin, morphine and codeine
What is the mechanism of action of opioids?
- Bind to opioid recepters (OP mu, Kappa, delta)
- Opioid receptors are G-protein coupled receptors and lead to inhibition of adenylate cyclase and reduction in cAMP
- Leads to K+ channels opening and an efflux of K+, leading to hyperpolarization
- Ca+ channels are inhibited, causing reduced transmitter release
- Ultimately this leads to a decrease of nociceptive impulses
Where in the body are opioids metabolized and excreted?
Metabolized: Liver
Excreted: Urine and Bile
Where in the nervous system are the opioid receptors found?
- Brain and CTZ
- Dorsal horn (sensory)
- Peripheral terminals of nociceptive afferent neurons
With regards to the pupils, what happens in our domestic species upon administration of opioids?
Dogs get pupil constriction
Cats, horses and ruminants get pupil dilation
With regards to thermoregulation, what happens in our domestic species upon administration of opioids?
Dogs get a hypothermia
Cats, horses and ruminants get a hyperthermia
What are the effects of certain opioids on the CVS?
- Pethidine/ Morphine: can cause a severe histamine release, which can cause severe vasodilation and death if untreated
- All opioids (except Pethidine) can cause Bradycardia
