Narcotics analgesics Flashcards
Three major opioid receptor types that are potential targets for narcotic analgesics
- µ (Mu)
- δ (Delta)
- k (Kappa)
What type of receptors are opioid receptors?
G-protein coupled receptors
Sites of opioid receptors regulating pain
- Peripheral nociceptive terminals (peripheral analgesia)
- Spine (spinal analgesia)
- Brain (Supraspinal analgesia)
Generally, how do opioid analgesics reduce pain?
- Inhibit propagation of pain signals
- Alter emotional perception of pain
- (possibly) elevate pain treshold
The opioid receptor most involved in pain mediation
µ receptor
The opioid receptor that is most associated with Dysphoria
k receptor
List the dose dependence effects of narcotic analgesics as dose increases, from therapeutic to toxic.
- –Therapeutic—
1. Peripheral Analgesia (Nociceptive terminals)
2. Spinal Analgesia (Spine)
3. Supraspinal Analgesia, (Brainstem)
4. Sedation (Brainstem)
5. Euphoria (Emotional Brain)
6. Cough suppression (Brainstem, Resp Nuclei) - –Toxic—
1. Pupil constriction (Oculomotor)
2. Constipation, Reduced gut motility
3. Dysphoria (Emotional Brain)
4. Severe Sedation (Brainstem)
5. Respiratory depression (Respiratory Nuclei)
What are some dosing considerations for:
- Elderly
- Type of pain
- Chronic pain
- Elderly: require lower dose to achieve effective pain relief than younger patients
- Type of pain: Neuropathic pain rq higher dose than nociceptive
- Chronic pain: Lower doses with continuous maintenance rather than administration in response to pain recurrence
General rule for dosing opioids
Start low, titrate carefully until sufficient analgesia is obtained, or until persistent unacceptable SE requires therapy re-evaluation
Characteristics of opioids in some patients with chronic pain
Opioids do not exert appreciable analgesic effect until threshold dose achieved
What does failure of partial analgesia with incremental in opioid-naive patient indicate?
Pain syndrome is unresponsive to opioid therapy. Other medications or procedures may be required, and opioids should not be used
OR
higher doses of opioids are rqeuired
List the clinical uses of opioid agonists, and name some drugs associated with each usage
- Analgesia: Codeine, morphine, pethidine
- Anaesthetic adjuvant: Fentanyl
- Cough suppressant/antitussive: Codeine
- Anti-diarrhoeal: Diphenoxylate
Name some strong Opioid Agonists
- Morphine
- Fentanyl
- Methadone
- Pethidine
Describe the properties of Morphine, methadone and Fentanyl such as:
- Opioid receptor binding
- Analgesia efficacy
- Concerns
- Strong µ agonist. Weaker agonist of other opioid receptors
- High Maximum analgesic efficacy
- Concern: High liability for addiction or abuse
Compare the duration of action between Methdaone and Fentanyl
Methadone is long-acting (half life > 24h) while Fentanyl is short-acting and used as an anaesthetic adjuvant