Pain Management Flashcards
Somatic (nociceptive) Pain
“Normal pain”
- originates in skeletal muscle, ligaments, and joints
- localized and constant (dull, sharp, aching)
- prostaglandin mediated: typically responds to NSAIDs (and opioids)
Visceral (nociceptive) Pain
“Vague, cannot pinpoint”
- Originates in smooth muscle (solid or hollow organs)
- Difficult to localize (diffuse, gnawing, crampy)
- Responds to opioid analgesics
Neuropathic (deafferentiated)
- Peripheral or central nerve injury, not stimulation
- Burning, tingling, shooting pain
- Poor response to analgesics- better response to adjuvant Tx
Emerging theme of pain management
- Over excited pain fibers
- Treat by: Diminishing excitation by hyperpolarizing nerve:
- -> Reduce influx of Na, Ca
- -> Increase influx of Cl
- -> Increase efflux of K
- Reducing release of pain eliciting neurotransmitters
- Enhancing inhibition
Opioid Receptor Function
- Found in ascending & descending pain pathways and in portions of the brain
- Most commonly used opioids are full mu receptor agonists
- No ceiling effect on analgesia
Mu receptor
Analgesia, sedation, respiration depression, constipation, euphoria
Kappa receptor
Analgesia, respiratory depression (< mu), sedation, constipation, dysphoria, psychomimetic
Delta receptor
Analgesia
Opioid Therapy is First Line for
- Acute severe pain
- Moderate to severe chronic pain related to cancer or other life threatening/limiting illness
Opiate
A drug (i.e morphine, heroin, codeine) containing or derived from opium and tending to induce sleep and to alleviate pain - From opium poppy
Opioid
Possessing some properties characteristic of opiates, but not necessarily derived from opium (fentanyl, methadone)
-Not necessarily from opium poppy
Mu agonist
- Type of opioid
- Relieves pain by binding to the Mu receptor in the nervous system
Mu antagonist
Drug that competes with an agonist for opioid receptor binding site (Mu receptor) but has no effect at the site
Mixed agonist/ antagonist
A type of opioid that binds to the kappa receptor as an agonist, but to the mu receptor as an antagonist
Partial agonist
A compound which possesses affinity for a receptor, but unlike a full agonist, will elicit only a degree of the pharmacological response, even if a high proportion of receptor are occupied by the compound
Route of Administration: Oral
- Significant first pass effect
- IV to PO dose conversions
Route of Administration: Parenteral
IV, IM, SubQ, PCA
Route of Administration: Transdermal
- Compliance benefit
- Disadvantage: cannot rapidly titrate opioid
Route of Administration: Neuraxial
- Epidural, intrathecal
- Allow for small doses, longer duration
Other routes of administration
- Transmucosal
- Rectal
- Topical
- Intranasal
Differences in efficacy between opioids
- No evidence of difference in efficacy of any opioid at equianalgesic doses
- Onset of action: fentanyl and derivatives quicker IV
- Duration of action: methadone naturally long acting, most other drugs formulated into long acting oral formulations
Mixed agonist- antagonist/ partial agonists
- Lower abuse potential
- “ceiling” effect on both side effects and analgesia- may not be effective for severe pain
- High psychotomimetic response due to Kappa stimulation
- May cause pain or precipitate withdrawal in patients currently receiving full mu opioid agonists
Acute opioid induced side effects
Common: constipation, cognitive impairment, sedation, nausea, itch
Less common: Sweating, myoclonus, urinary retention, respiratory depression, dry mouth, headache
Chronic opioid induced side effects
Amenorrhea, sexual dysfunction, immune dysfunction, QTc prolongation (methadone)
