What is mechanism of action for opioids?
- Act at pre and post synaptic receptors
- present in the peripheral and central nervous systems
What are the different types of opioid receptors?
- OP1 - delta
- OP2 - kappa
- OP3 - mu
Where is the delta receptor located? What does stimulstion of this receptor result in?
- Located in the limbic system of the brain
- stimulation results in analgesia and modulation of mu receptors
Where is te kappa receptor located and what does stimulation of this receptor result in?
- Located in cerebral cortex and spinal cord
- stimulation results in spinal analgesia, mild sedation, diuresis, and miosis
Where is the mu receptor located and what does stimulation of this receptor result in?
- Located throughout the brain and in the dorsal horn of the spinal cord
- stimulation results in profound analgesia, euphoria, sedation, miosis, respiratory depression, chemical dependence, inhibition of GI motility, ADH release, can cause panting in dogs
What does stimulation if the sigma receptor result in?
What do sigma receptors do?
Sigma receptors bind to opioid and several non-opioid drugs and have no affinity for the opioid reverser agent naloxone
What are the side effects and contraindications for opioids?
- Decreased heart rate
- dysphoria in cats (reduce dose, give tranquilizer)
- contraindicated in patients with suspected intracranial hypertension
Synergistic analgesic effects with...
- alpha 2 agonists
- local analgesics
What are the two categories for deciding which opioids to use?
- mild to moderate pain
- moderate to severe pain
Which opioids can we use for mild to moderate pain?
- fentanyl patch (Duragesic)
- butorphanol (Torbugesic)
- buprenorphine (Buprenex)
Which opioids can we use for moderate to severe pain?
- oxymorphone (Numorphan)
- hydromorphone (Dilaudid)
What are some opioid antagonists?
- naloxone hydrochloride (Narcan)
- levallorphan tartrate (Lorfan)
- nalorphine hydrochloride (Nalline)
What receptors does butorphanol affect?
- mu antagonist
- kappa agonist
Which receptors does buprenorphine affect?
partial mu agonist
Which receptors does morphine affect?
Which receptors does tramadol affect?
partial mu agonist
Which receptors does naloxone affect?
Which receptors does levallorphan tartrate affect?
mixed agonist - antagonist
Which receptors does nalorphine hydrochloride affect?
mixed agonist - antagonist
What is the mechanism of action for local analgesics?
prevent conduction of nerve impulses by inhibiting passage of Na through nerve cell axon membranes
What are the side effects and contraindications for local analgesics?
excessive overdoses or accidental IV injection can cause CNS toxicity (seizures) and cardiovascular toxicity
What happens when we give local analgesics with general anesthetics?
reduces the dose of general anesthetics needed
What are some local analgesics?
- lidocaine (Xylocaine)
- bupivacaine (Marcaine)
- mepivacaine (Carbocaine)
What is the mechanism of action for alpha 2 agonists?
- activation of alpha 2 receptors
- cause the neurons to become unresponsive to excitatory input
- inhibits release of norepinephrine
What are the side effects and contraindications of alpha 2 agonists?
- can cause severe bradycardia
- avoid in patients with cardiac problems
- vomiting may occur, especially in cats
What are alpha 2 agonists synergistic with?
- and many general anesthetic drugs
What are some alpha 2 agonists?
- xylazine (Rompun)
- medetomidien (Domitor)
- detomidine (Dormosedan)
What are some alpha 2 antagonists? And what do they reverse?
- yohimbine (Yobine) - reverses xylazine
- atipamezole (Antisedan) - reverses medetomidine
What is the mechanism of action for NSAIDs?
- inhibit COX (cyclooxygenase)
- older NSAIDs are general COX blockers and also block protective GI and renal prostaglandins
- newer NSAIDs more specifically block COX-2 and inflammatory prostaglandins that sensitize peripheral nociceptors
What are the side effects, contraindications, and toxicities of using NSAIDs?
- use cautiously in cats
- monitor long term use with lab work and use lowest effective dose
- use cautiously in bleeding disorders or close to surgery time (reduces platelet function)
- use cautiously in patients with GI bleeding or renal disease (may suppress good prostaglandins)
When are renal prostaglandins released?
under low renal blood flow conditions to cause renal vasodilation
What can NSAIDs enhance in the GI and renal?
toxicity of corticosteroids
What are some examples of NSAIDs?
- carprofen (Rimadyl)
- etodolac (Etogesic)
- meloxicam (Metacam)
- ketoprofen (Ketofen, Orudis, Anafen)
- robenacoxib (Onsior)
- flunixin meglumine (Banamine)
- meclofenamic acid (Arquel)
- tolfenamic acid
- acetaminophen (Tylenol)
Which NSAIDs are approved in cats?
Which NSAIDs are hard on dog and cat GI systems?
Which NSAIDs are toxic to cats?
What is the mechanism of action for analgesic adjuvant agents?
- have primary medical indications other than pain
- enhance analgesia by interacting with a variety of receptors or interfering with nerve conduction
Which drugs should we avoid using with analgesic adjuvant agents?
avoid combining NSAIDs and corticosteroids in the patient - increased risk of GI ulcers and nephrotoxicity
What are some analgesic adjuvant agents?
- phenothiazine (acepromazine)
- benzodiazepine (diazepam)
- corticosteroid (prednisolone)
- tricyclic antidepressant (amitriptlyine)
- anticonvulsant (phenytoin)
- antiarrhythmic (mexilitine)
- beta-adrenergic blocker (propranolol)
What is a transdermal analgesic?
How do we administer a transdermal analgesic?
- place firmly on a clipped region
- cover with a bandage
- apply 12 - 24 hours before surgery
- use other opioids as needed to supplement
What are some non-pharmacologic methods of pain control?
- nutraceuticals (Cosequin)
- physical rehab techniques - massage, therapeutic ultrasound, hydrotherapy, exercise, homeopathy, chiropractics, acupuncture, laser therapy