Opioid Analgesics Flashcards
What is an Opiate?
Compounds structurally related to opium products.
What is an Opioid?
- An agent w/ functional and pharmacological properties of an opiate.
- Opium-like compound that binds to one of three receptors.
What is a narcotic?
Substances that blunt the senses.
Legal Term: Harrison Narcotic Act 1914.
Opioid Analgesics compared to non-opioid:
- Produce Tolerance
- Produce psychological & physical dependence.
- Greater efficacy for pain.
- Good for Cardiac, Visceral pain.
- Site of action is central
- Have different side effect profiles
- Are structurally quite homegeneous.
What do Endorphins contain?
endogenous opioid peptide
31 aa, containing met-enkephalin
What do Enkephalins contain?
Endogenous opioid peptide
5 aa, leu- & met-enkephalin
What do Dynorphins contain?
Endogenous opioid peptide
13-17 aa, containing leu-enkephalin.
What is the distribution of opioid receptors?
- Brain
- Spinal Cord
- Enteric nervous system (lining of esophagus, stomach, small intestine and colon)
What are the 4 opioid peptide precursors?
- Proorphanin
- Prodynorphin
- Proenkephalin
- POMC
What are the endogenous ligands of mu1 supraspinal and mu2 spinal receptors subtypes?
- Beta endorphin
more than met- and leu-enkephalin endomorhpin-1 - Dynorphin A more than B
What are agonists for the mu1 and mu2 opioid receptor subtypes?
- Morphine
2. Other pure agonists.
What effects do agonizing mu1 receptor subtypes cause?
- Supraspinal analgesia
- Sedation
- Hypothermia?
- Euphoria
- Physical dependence
What effects do agonizing mu2 receptor subtype cause?
- Spinal analgesia
- Sedation
- Respiratory depression
- GI tract decrease transit.
- Bradycardia
What are the endogenous ligands for delta receptor subtypes?
- met- and leu-enkephalin
2. Beta endorphin
What are agonists of the delta receptor subtype?
- Sufentanil (weak)
How many kinds of delta receptor subtypes are there?
2
What effects do agonizing delta receptor subtypes cause?
- Analgesia
- Anti-depressant effects
Less than mu agonists - GI
- Dependence
- Respiratory depression
What are the endogenous ligands of kappa receptor subtypes?
- Dynorphin A & B.
What are agonists of the kappa receptor subtype?
- Butorphanol more than other
2. Partial agonists/antagonists.
How many kinds of kappa receptor subtypes are there?
3
What effects do agonizing kappa receptor subtypes cause?
- Spinal (k1) and supra spinal (k3) analgesia
- Miosis?
- Physical dependence
- GI tract decrease transit
- Aversive behavioral effects including
- Psychotomimesis/Dysphoria - Sedation
- Diuresis
What are common actions of all opioid receptor subtypes?
- Each coupled to Gi/G0
- Galpha protiens
- Inhibit adenylate cyclase
- Negatively coupled to Voltage dependent Ca channels
- L and N type (reduce opening) - Promote K current (efflux) hyperpolarization.
- Activation of PKC and PLCbeta
What are the opioid classifications by source?
- Natural (morphine & codeine)
- Semi-synthetic
- Synthetic
What are the opioid classifications by structure?
- Phenanthrenes
- Phenylpiperidines
- Diphenylheptane
What are examples of Phenanthrenes?
- Buprenorphine, Butorphanol, Codeine, Dezocine
- Hydrocodone, Hydromorphone, levorphanol, morphine
- Nalbuphine, oxycodone, oxymorphone.
What are examples of Phenylpiperidines?
- Alfentanil
- Fentanyl
- Mepiridine
- Sufentanil
What are examples of Diphenylheptanes?
- Methadone.
What are the roles of endorphin?
- Placebo
- Acupuncture
- Labor/Delivery
What are the properties of Morphine?
Agonist of mu receptor subtype
- standard dose = 10mg IM for 70kg adult.
- PO F 0.25, due to 1st pass metabolism
- Rectal F 0.25
- SC F 0.5
- IM
- Good if good blood flow through the muscle
What is the Distribution of Morphine?
- Everywhere including fetus!
2. PPB 35%
What is the metabolism of Morphine?
- half life 2 hours
2. Role of morphine-6-glucuronide in effects.
What are the important metabolites of morphine?
- M3G
2. M6G
What percent of Morphine is metabolized into M3G and through what?
- 90%
2. UGT2B7
What percent of Morphine is metabolized into M6G and through what?
- 10%
- UGT2B7
- Effective metabolite
- M6G trapped in the brain
- 100X higher affinity for receptor.
What are the CNS actions of Morphine type opioids?
- Euphoria - rapid tolerance
- Drive satiation
- Sedation
- Analgesia (sensory modality specific)
- Increase pain threshold
- Change perception of pain. - Respiratory depression
- RR decreases by 33% - cough suppression (antitussive)
- Hypothermia
- N&V
- Pupillary reaction
How do morphine type opioids change the perception of pain?
- Act on thalamus & modulate connections to limbic system.
What is the main cause of OD death?
Respiratory Depression
What are the mechanisms for respiratory depression of morphine type opioids?
- Depress neurogenic drive (dorsal & ventral medullary respiratory neurons)
- Decrease response to increased CO2
- Medullary chemoreceptors
- Aortic body chemoreceptors
When should Morphine type opioids be used with caution?
In pts w/ compromised respiratory function, sleep apnea, COPD, asthma, emphysema.
What is the mechanism of cough suppression for morphine like opioids?
- d-isomers of opioids: Codeine, hydrocodone, dextromethorphan
- Analgesic activity is in I-isomer
- Medullary cough center (cough receptor in throat reflex to this)
- 25% of analgesic dose.
What actions do d-isomers of morphine like opioids lack?
- Respiratory depression
- Analgesia
- Tolerance
- Drowsiness
What is an inappropriate use of morphine like opioids?
Productive cough.
What pupillary reaction is involved in actions of morphine like opioids?
- Miosis - constriction
- Oculomotor nerve, edinger-westphal nucleus
- General lack of tolerance
How does N&V with morphine like opioids?
- Biphasic chemoreceptor trigger zone stimulation followed by blockade.
- Role of vestibular stimulation
How do you deal with N&V b/c of morphine?
- Reduce physical activity
- Dosage schedule
- Anti-emetics: transdermal scopolamine, promethazine.
What actions do Morphine type opioids have on the CV system?
- little effect on HR, and CO
- Decreased workload due to decreased left ventricular diastolic pressure, cardiac work & decrease venous return.
(NOT produced by partial agonist-antagonists)
When is the action of morphine type opioids used regarding the CV system?
MI, acute pulmonary edema, CHF.
What other cardio effects do morphine type opioids have?
- Orthostatic hypotension.
What is the difference b/w opioid induced histamine release and Type 1 IgE mediated hypersensitivity?
- Non-allergic (histamine release)
- Drug allergy (on re-challenge)
- very rare
- IgE
What is seen with opioid induced histamine release?
- Pruritis
- Flushing
- Hives
- Hypotension
What is seen with Type 1 IgE mediated opioid hypersensitivity?
- Hives
- Bronchospasm
- Respiratory distress
- Laryngeal edema
- Hypotension
- Acute cardiovascular collapse
What effective dose of morphine type opioids produce smooth muscle effects?
Increased tone
less than analgesic dose: 2-4 mg, codeine 15-30 mg
What effects do morphine type opioids have on GI?
- Decreased GI motility
- Constipation
- Inhibits peristalsis but does NOT stop mixing action (cramping)
What are the treatments for GI issues with morphine?
one or more of the following:
- Stool Softener (emollient lubricant: docusate)
- Stimulant cathartic (Senna, Bisacodyl, Cascara)
- Saline cathartic
- PEG 3350
- Opioid receptor antagonists.
Increasing the tone of smooth muscle by morphine like opioids causes what in the biliary tract?
- Contraction of Sphincter of Oddi
2. Increased pressure in gallbladder.
Increasing the tone of smooth muscle by morphine like opioids cause what in the urinary bladder?
- Contraction of Detrusor muscle and trigone muscle
2. Urinary retention.
Why is Morphine used as an analgesic in palliative care?
- Prevent and relieve suffering and to support the best possible quality of life for patients and their families, including effective pain management.
When is morphine used as an analgesic in obstetrics?
- Epidural
Why is morphine used as an analgesic for MI?
- Decrease Cardiac work, sedation.
What is the possible negative effect in using morphine for analgesic effects during pre- and post-surgery?
- May prolong recovery, due to activation of microglia.
What kind of pain is exhibited in Fibromyalgia?
- Chronic non-malignant pain, fatigue, sleep problems.
What is the treatment for acute low back pain?
Less than 2 weeks
- NOT opioids due to physical dependence
- NSAIDs, APAP, skeletal muscle relaxants, physical therapy.
What is the treatment for chronic low back pain?
More than 3 months, due to spinal abnormalities, disk herneation.
- NOT opioids
- Risk of physical dependence
- Opioids increase time out of work and medical expense. - Exercise to strengthen muscles, manipulation.
What is the WHO 3-step analgesic ladder?
Step 1: Mild to Moderate Pain
-Non-opioid +/- adjuvant agent
Step 2: Mild to Moderate Pain or Pain uncontrolled after step 1.
- Short acting opioid as required +/- non-opioid ATC +/- adjuvant agent.
Step 3: Moderate to Severe Pain or Uncontrolled after step 2.
-Sustained release/long acting opioid ATC or continuous infusion +/- short acting opioid as required +/- non opioid +/- adjuvant therapy.
What are the long acting oral dosage forms?
- Kadian
- MS Contin
- Oramorph SR
- Avinza
- immediate and ER beads in capsule.
Where should opioids be injected in the spinal cord?
- Into Cauda Equina
- Spinal nerves present but not solid cord
- Less risk of SCI
When is intraspinal administration used for chronic pain?
- Typically when standard treatments fail.
What two drugs are FDA approved for intrathecal administration for chronic pain?
- Morphine & Ziconotide
What is Ziconotide?
NON-Opioid
- N-Type voltage sensitive Ca channel blocker that blocks neurotransmitter release from presynaptic primary nociceptive afferent nerve terminals
- Approved for chronic pain in patients who do not tolerate or respond to other treatments.
What is Codeine?
3-methylmorphine
- Morphine pro-drug
- Oral administration (more complete than morphine)
- CYP2D6 metabolized