Opioids Flashcards
Mechanism of action of opioids
Act on mu, kappa & delta which are Gi protien-couples receptors in CNS & periphery
Act at afferent pain-conducting fibers (peripheral analgesia), spinal cord (spinal analgesia), brain (suoraspinal analgesia). Limbic system (euphoria & dec emotional response to pain)
At cellular level, inhibit Ca++ influx & release of excitatory NT presynaptically while stimulating K+ influx postsynaptically causing hyperpolarization.
The opioid partial agonist is ….., while the weak opioid analgesic is ……
Buorenorphine
Propoxyphene
…&…. are metabolized into morphine
Heroin,codeine
Mention uses of opioids
Analgesic
Anesthetic
Acute pulmonary edema in LVF following MI
Antitussive
Antidiarrheal
Mention analgesic uses of morphine
Chronic visceral pain
Postoperative/cancer pain
Acute trauma
MI
Mention the main effects of morphine
Analgesia, euphoria, sedation
Mention the inhibitory effects of morphine
Inhbits:
VMC, VD
Respiratory center, inc CO2 causing cerebral VD & inc intracranial tension
Cough center
Uterine tone
Thermoregulatory center
Enumerate stimulatory effects of morphine
Stimulate:
Occulomotor nucleus (miosis)
CTZ
Urinary & GIT walls, inc tone of sphincters (spasmogenic) & dec walls peristalsis
Histamine release
Mention the antitussive & antidiarrheal opioids
T: codeine, dextrimethorphan
D: loperamide, diphenoxylate
Mention the contraindications of morphine
Acute undiagnosed abdominal pain
Normal labour pain
Closed head injury
Biliary colic & enlarged prostate
Asthma
Extremes if age, hypothyroidism, liver dysfunction
Peptic ulcer
GR: Morphine is CI in normal labour pain
Because it causes uterine relaxation and can delay normal labour
Also can cross the placenta and cause respiratory center depression of the fetus keading to Asphyxia Neonatorum
GR: Morphine is CI in closed head injury
Because morphine may increase intracranial pressure and increase brain damage.
Mention uses of methadone
- Treatment of opioid addicts
- Analgesic in severe chronic pain
GR: methadone is used in Treatment of opioid addicts
Because it is orally active & long acting thus used to replace morphine/heroin. Its gradual withdrawal is associated with less severe & smoother withdrawal symptoms
Mention a sode effect specific to methadone
Prolong QT interval, inc risk of torsades de pointes
Enumerate differences between pethidine & morphine
Pethidine is:
1. Less constipating (short acting)
2. Less respiratory depression in newborn & does not delay labour
3. Atropine-like actions
4. Inc risk of convulsions in higher doses due to accumulation of toxic metabolite norpethidine (not used for more than 48 hrs)
Mention a side effect specific to fentanyl
Chest wall rigidity, dec thoracic compliance & dec ventiallation with higher doses
Uses of fentanyl
Analgesic in severe pain
Anaesthesia (preanesthetic medication & in CV surgery)
Conscious sedation, neurolepanalgesia, neurolepanaesthesia
…..is more potent than fentanyl, while …..is ultra-short acting
Sufentanil
Remifentanil
Mention the advantages & disadvtanges of tramadol
Adv: less constipation, respiratory depression & addiction
Dis: inc risk of convulsions
Mention advantages of buprenorphine
Less addiction
Respiratory depression is not dose dependent due to ceiling effect but if it occurs more difficult to reverse due to higher receptor affinity
Mention uses of partial agonists
Analgesic in severe pain
Alternative to methadone for treatment of opioid addict
Discuss drug interactions of opioids
- Opioids + other CNS depressants = additive CNS depression
- Pethidine + MAOI = serotonin syndrome
- Pure + partial agonist = withdrawal symotoms & dec analgesic effect
Treatment of acute morphine toxicity & signs of improvement
Support respiration
Naloxone (opioid antagonist)
Increase in respiratory rate & pupillary dilation
Uses of naloxone & naltrexone
- Acute opioid toxicity, Asphyxia neonatorum
- Opioid & alcohola abuse
When should naltrexone be given to addicts & why?
After full detoxification
To avoid precipitation of withdrawal syndrome
List steps of treatment of addiction
- Symptomatic treatment (NSAIDs for pain, antiemetic)
- Sympatholytic e.g. clonidine
- Detoxification replace with methadone or buprenorphine then gradual withdrawal
- Maintenance with Naltrexone (block euphoria of opioids)
