308 Pharmacology of pain control Flashcards
What are the different causes of nociceptive pain?
Somatic: Activation of nociceptors in skin, muscle and bone
Visceral: activation of nociceptors from stretching, distension or inflammation
Describe the WHO analgesic ladder
- non-opioid
Eg. Paracetamol, Aspirin, NSAIDs - Weak opioid
Eg. Tramadol, Codeine, Dihydrocodeine - Strong opioid
Eg. Morphine, Oxycodone, Fentanyl, Diamorphine, Alfentinil, Hydromorphine
+/- adjuvants
What are some pharmacological adjuvants used beside the WHO analgesic ladder?
-Corticosteriods
-Antidepressants
(duloxetine, amitriptyline, mirtazepine)
-Antiepileptics
(gabapentin, pregabalin)
-Anti-muscarinics
(mebeverine, hyoscine)
-Benzodiazepines
-Bisphosphonates
-Ketamine
What are some non-pharmacological adjuvants beside the WHO analgesic ladder?
-TENS
-Acupuncture
-Massage
-Heat
-Psychological support and relaxation
-Radiotherapy
-Interventional techniques
(stenting etc.)
What are the 3 subtypes of opioid receptor?
Mu, Kappa, and Delta
Where are opioid receptors found?
CNS
Eg. cortex, thalamus, hypothalamus, PAG, RVM
Other
Eg, enteric plexus of gut, peripheral sensory afferent nerves, dorsal root cells, immune cells
What is the endogenous opioid and effect of binding on each type of opioid receptor?
Mu - Beta-endorphins
Effect: Analgesia (brain and spinal cord), respiratory depression, euphoria, miosis, constipation
Kappa - Dynorphins
Effect: Analgesia (spinal cord), dysphoria, miosis, diuresis
Delta - Enkephalins
Effect: analgesia (Spinal cord), respiratory depression
What are the effects of opioids?
Analgesia
-Anti-nociception and effect on emotional response
-Direct inhibition of ascending transmission of nociceptive information from the spinal cord dorsal horn
-Activation of descending pain control circuits from the midbrain to the dorsal horn
Psychotropic
-Anxiolysis and euphoria may also help with analgesic properties
Respiratory depression
-Direct effect on respiratory centre in medulla Eg. Oramorph for SOB in patients with end stage COPD
Suppression of cough reflex
Eg. Codeine linctus for cough
Constipation
Delayed gastric emptying and inhibition of peristalsis. Eg. Codeine for high output stoma
What are some adverse effects of opioids?
Constipation
-Consider a less constipating opioid if constipation is problematic (e.g. fentanyl)
-Offer a laxative (combination stimulant e.g. senna and softener e.g. docusate)
-Consider a peripherally acting opioid receptor antagonist (naloxogel) for severe constipation where opioid cannot be withdrawn
Nausea and vomiting
-Offer an anti-emetic
-Usually resolves after 5-7 days
Sedation
-Advise of this side effect. Advise not to drive / operate machinery after commencing / increasing dose
- Delirium, hallucinations
Dry mouth
-Advise sugar free chewing gum, saliva substitutes, mouthwash
Pruritus
-Offer an antihistamine
What are the symptoms of opioid toxicity?
Drowsiness
myoclonic jerks
pinpoint pupils (miosis)
respiratory depression
agitation
confusion
vivid dreams
hallucinations
In what forms is fentanyl prescribed?
Patched or lozenges/intranasal
What is the first line drug for level 3 of the WHO analgesic ladder?
Morphine
