Analgesic Drugs Flashcards
(23 cards)
Nociception
“Detection of noxious stimuli or stimuli that are capable of damaging tissue”
4 pain processes
Transduction: damage has happened, to primary afferent nociceptor
Transmission: primary afferent nociceptor to spinal cord
Modulation: can interrupt the pain pathway and cause less pain
Perception: brain receives stimulus and makes you consciously aware of the pain
Nociceptive stimulus causes what type of pain?
Acute pain
Neuropathic Pain
- “pain induced by injury to or disease of the somatosensory system”
- develops slowly, outlasts healing of original injury
- allodynia, hyperalgesia, causalgia (burning)
Analgesic Drugs
Selectively blocks the sensation of pain without blocking other symptoms or loss of consciousness
Anesthetic
- Local anaesthetic blocks nerve conduction and all local sensations (including pain)
- General anaesthetics cause loss of sensations and unconsciousness
Opioids
- Higher centres of CNS
- Pain can still be felt but produces less suffering
- During perception - Reduces neurotransmitter released from terminals pain fibres in dorsal horn of spinal cord
- During modulation
Bind to opioid receptors
All opioid analgesics are full agonists or partial agonists at receptors
Opiate
Any drug derived from opium
- Morphine
- Codeine
Opioid Receptors
mu receptors
- Analgesia
kappa receptors
- Analgesia
- Dysphoria and hallucinations
Pharmacological Properties of Opioids
- Analgesia (u and k)
- Sedation and Mental clouding
- Euphoria and Tranquility (u and k)
- Antitussive
- Depression of Respiratory Centre (u)
- Nausea, vomiting
- Miosis - pin-point pupil (u and k)
- tolerance and serious dependence (u)
- Constipation (u and S)
- Postural hypotension
- Dilation of cutaneous bv (warm skin)
- Urinary urgency but difficulty in urination
- Biliary colic and epigastric distress
Examples of Opioids
Heroin (diamorphine) Morphine Methadone (longer action than morphine) Fentanyl Codeine Oxycodone Loperamide (Imodium – no CNS action)
Opioid Analgesics - Indications
Main - To alleviate mild to moderate to severe pain
- Often given with adjuvant analgesic agents to assist with pain relief
Also used for
- cough suppression (codeine)
- treatment of diarrhea (loperamide)
- balance anaesthesia (fentanyl)
Morphine
*Morphine sulfate
- Acute and chronic pain - less effective in neuropathic pain
- “The standard” for drugs
- Primarily affects mu opoiid receptor
- t 1/2 = 2-4 hours
Extensive liver metabolism
- Inactivation
- First pass metabolism
- IV is 3-4x more effective than po
Pregnancy/breast feeding
- Risk for physical dependence
- Crosses placenta
- Enters breast milk
Analgesics and Cancer Pain
Chronic pain
- requires fixed schedule around-the-clock treatment
- opioids, NSAIDs, adjuvants
- eg. morphine sulphate (MS) Contin
Breakthrough pain
- transient episodes of pain while chronic pain is controlled
- access to rescue medication
WHO Pain Management Ladder
- Non-opioid + Adjuvant
- Opioid for mild to moderate pain + non-opioid + adjuvant
- Opioid for moderate to severe pain + non-opioid + adjuvant
NSAID’s and Adjuvant - Cancer Pain
NSAID
- the most common non-narcotic analgesic
Adjuvants
- antidepressants eg. amitriptyline (Elavil)
- antiseizure drugs eg. carbamazepine
- glucocorticoids
Morphine - Contraindicaitons
- Known drug allergy, hepatic dysfunction
- Severe asthma or other respiratory insufficiency
- Respiratory depression
- Elevated intracranial pressure (ICP)
- Pregnancy
Opioid Analgesics - Adverse
Main - Respiratory Depression - CNS depression with possible coma - Nausea and vomiting (1-3 days) - Constipation - no tolerance development \_\_ - Hypotension - Histamine release - Urinary retention - Diaphoresis and flushing - Pupil constriction (miosis)
Opioid Analgesics - Interactions
CNS depressants have cumulative effects
- eg. antipsycotics, sedatives, (benzodiazepines, barbiturates)
- ethanol
Codeine
Moderate Opioid Analgesics
- Less analgesia and respiratory depression
- Less metabolism to morphine (~10% of oral dose)
- Antitussive
- Often combined acetaminophen in T1, T2, T3
- Acetylsalicylic acid in 222’s or 292
Oxycodone
Moderate Opioid Agonists Oxycontin or Percodan - metabolism required for activation - similar to codeine effect - abuse potential - widely used with acetaminophen (Percocet)
Naloxone
Opioid Antagonists
Narcan, naltrexone
Antagonistic
Used for complete or partial reversal of opioid-induced respiratory depression
Shorter half life than other opioids (1-2 hours)
Opioid Analgesic - Implications
Oral forms should be taken with food to lessen gastric upset
- Withhold dose if respiratory rate is less than 12 breaths/minute
Constipation:
- Should take with adequate fluid and fibre intake
- Usually stool softener (docusate) used daily when started on codeine
Orthostatic Hypotension
