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Opiods
strong analgesics
- uses
- mechanism
- classes and members
- dose and half-life
- adverse drug reactions
- counter-indications and drug interactions
- metabolism and excretion
- dependency
Uses
Opioids are a serious class of drug.
- analgesia
- anaesthesia
- cough suppression
- antidiarrheal action
Mechanism
- acts on μ receptors in the CNS; see mechanisms of morphine for more details
Classes and Members
μ agonists
weak
- codeine - must be metabolized
moderate
- oxycodone
potent
- morphine
- methadone
- meperidine
- hydromorphone - highly lipid soluble
- heroin - highly lipid soluble
- fentanyl
κ agonists and μ antagonists
- pentazocrine
- nalbuphine
- buprenorphine
opioid antagonists
- naloxone
- naltrexone
Starting a Patient on Opioids
pick a drug
oxycodone (5 mg po Q4h + 3 mg po Q1h prn)
morphine (5mg po Q4h + 3mg po Q1h prn)
hydromorphone (1 mg po Q4h + 0.5-1.0 mg po Q1h prn)
long-acting formulations
Only when patients has reached a stable q4h dosing should a stable, long acting formulation be considered
Equivalent Dosing
comparing to morphine
PO (mg) |
IV/SC (mg) |
|
morphine |
10 |
5 |
hydromorphone |
2 |
1 |
codeine |
100 |
|
fentanyl patch |
5 ug/hr |
|
oxycodone |
5-7.5 |
increase dosing by 50% if pain is unrelieved
dosing: PO takes close to an hour
SC: 15 minutes
IV: 5-10 minutes
Adverse Drug Reactions
always warn people and say they are to be expected; they will likely think they are allergic....
- sedation and CNS depression
- respiratory depression: not common; increased risk factors include opioid naive people, rapidly escalating dose, IV drip, other drugs, kidney impairment/volume depletion, concurrent CNS drugs, ie benzos, anticholinergics
- mood changes
- hypotension (arterial vasodilation)
- myoclonus, hyperalgesia/allodynia, delirium, hallucinations
- nausea, vomiting
- constipation, urinary retention
- dry mouth, pruritis, urticaria (hives)
Tolerance
- repeated administration produces less effect; can be a problem with chronic pain
- involves PKC-mediated phosphorylation of the μ receptor
Physical Dependence
- involves overactivity of cAMP following long term suppression
- withdrawal produces physical abstinence syndrome
- mild: lacrimation, yawning, sweating
- moderate/severe: anorexia, xramps, nausea, vomiting, restlessness, irritability, tremor, tachycardia, hypertension, chills, spasms, goosbumps
Psychological Dependence
- involves activation of endogenous reward systems
Addiction
- combination of physical and psychological dependence
- involves psychosocial factors
- continued drug seeking despite knowledge of harmful effects
- behaviour becomes a preoccupation and detriment
Treatment
- methadone
- detoxification (withdrawal from opioid)
- long term blockade with naltrexone
- psychosocial support
Counter-Indications and Drug Interactions
- fentanyl is inactivated by P450; potent P450 inhibitors should accordingly be used with caution
Metabolism and Excretion
- metabolized in the liver and excreted through the kidney