Opioid Agonist Flashcards
General structures of opioid Agonist
Pheantherenes:
Morphine, codiene, Thebaine-
Structure Benzylisoqinolone:
Papverine and Noscapine
Opioid agonist MOA
Same receptors are activated by endogenous enkephalins, endorphins, and dynorphins
‣ Presynaptic inhibition of ACH, dopamine, NE, and Substance P
‣ Increased K conductance → HYPERPOLARIZATION
‣Ca + channel inactivation → Decreased neurotransmission
Opioid Agonist Uses
- Analgesia
2.Sedation - Anti-shivering
4.Cough suppression: Codeine, dextromethorphan
General CV effects
Bradycardia from histamine release
Hypotension
Orthostatic hypotension induced syncope
NITROUS AND BENZO= ↑ CV DEPRESSION (CO&BP)
BENEFIT: cardioprotective from MI
Direct depression of SA and AV node
Opioid General CNS
Miosis,
Sedation,
Myoclonus
delta waves on EEG
Tolerance: 2-3 weeks, down regulates receptors
Depressed respiratory center (Pons/Medulla)
Depressed medullary cough center
Caution with use in head injury!Decrease in CBF
*Skeletal muscle rigidity of thoracic & abdominal
Worsened with mechanical ventilation, treat with muscle relaxers or naloxone
Receptor µ1 (Mu1)
µ1 (Mu1): Analgesia (supraspinal, spinal )
Eupohoria, low abuse potential, miosis Bradycardia, hypothermia, urinary retention.
Mu1: “slow cold cant see cen’t bee but happy”
Receptor µ2 (Mu2):
µ2 (Mu2): Analgesia (spinal)
Depressed ventilation, physical dependence Constipation (marked)
Mu2: Can’t breathe, can’t poo - addicted too!”
Receptor K (Kappa):
K (Kappa): Analgesia (supraspinal, spinal)
dysphoria, sedation, low abuse, misosis, Diuresis
Receptor Delta:
Delta: Analgeisa (supraspinal, spinal)
Depressed ventilation, physical dependence
constipation (minimal) , urinary retention
Receptors Overview
Opioids Respiratory Overview..
‣ ↓ response of ventilation centers to CO2, and this will require higher ETCO2 for them to start breathing again. CO2 NARCOSIS is an issue - if CO2 too high like 60
‣increase in resting PaCO2 (shifts curve to the right).
‣MU2 → ventilatory depression, ↓ rate but ↑ in TV (Vm doesn’t change)
‣ overdose will induce apnea, miosis, hypoventilation, and coma
‣ reversal of ventilatory depression with physostigmine! it increases levels of ACH in CNS to antagonize the ventilatory depression but does not effect the analgesia.
‣ Pre- induction dose of opioids can induce coughing
Opioid GI general
GI:
Sphincter of Oddi Spasms (can mimic MI pain)
‣ Fentanyl 99%
‣ Meperidine 61%
‣Morphine 53%
Treatment: Nalaxone or Glucagon (2 mg IV, incremental doses), glucagon preferred b/c no opioid analgesic antagonism.
If these do not relieve pain then give nitro for MI pain.
Delayed Gastric Emptying and constipation
N/V: direct stimulation of the CTZ (chemoreceptor trigger zone)
Opioid Misc:
Rigidity: chest wall and abdominal muscles
Cutaneous: Skin flushing d/t histamine
Hormonal: decreased cortisol
PLACENTAL CROSSING–> NEONATE DEPRESSION or chronic use causes dependence
Opioid General GU
Urinary urgency/retention
Withdrawl:
Initial symptoms: yawning, diaphoresis, lacrimation, or coryza, insomnia and restlessness
72 hrs: Abdominal cramps, N/V, and diarrhea
Least to most potent
Codiene: (120mg = 10 mg morphine)
Meperidine: (pethidine) 1/10th
potency of morphine
Morphine:
Hydromorphone: (5x more potent than morphine)
Alfentanil: (1/5th less potent than fentanyl)
Fentanyl: (sublimaze)
75 to 125 x more potent than morphine
Remifentanil: 15-20 x as potent as alfentanil
equipotent to fentanyl- so the order of these two is subjectional
Sufentanil:
(5-12 x more potent than fentanyl)
MOA for Meperidine (pethidine)
Agonist at 𝝻 and K receptors
Also agonist at alpha 2 receptors
MOA for Remifentanil
Selective µ opioid agonist
Structure of Meperidine
Structural similar to
lidocaine: tertiary amine, ester group and lipophilic phenyl group
Atropine (causes similar effect of spasms of muscle)
Structure of Hydromorphone
Morphine derivative
Structure of Alfentanil
Meperidine analoge
Structure of Fentanyl
meperidine analogue
Structure of Remifentanil
Ester structure
Meperidine analogue
Sufentanil
Analogue of fentanyl (1974)
meperidine analogue
Codiene clinical uses
Cough suppressant
analgesic
Meperidine Clinical Uses
Intrathecal administration
IM for postop analgesia
Post op shivering because of K and a2 receptors
***clonidine also works for postop shivering at a2 receptors
Morphine Clinical Uses
Relieves visceral, skeletal muscles, joints and integumental dull > sharp (better for post op c-fiber pain)
intermittent pain
Hydromorphone clinical uses
same as morphine
Relieves visceral, skeletal muscles, joints and integumental dull > sharp (better for post op c-fiber pain)
intermittent pain
Fentanyl Use Cases
Cardiopulmonary bypass (***drug may adhere to circuit lessening amount of fentanyl in blood)
induction and analgesia
adjunct for
Direct laryngoscopy during intubation
Sudden changes in surgical stimulation level
Remifentanil Use Cases
Carotid endarectomy cases per CASTILLO
Induction & maintenance
Sufentanil Use Cases
Analgesia and induction
Analgesia: 0.1 to 0.4 µg/kg IV
Induction: 18.9 µg/kg IV
Intraop: 0.3 to 1 µg/kg IV
Infusion: 0.5 to 1 µg/kg/hr IV
Alfentanil Use Cases
Induction laryngoscopy: 15 to 30 µg/kg IV (90 seconds prior)
Induction alone: 150 to 300 µg/kg IV
Maintenance: 25 to 150 µg/kg/hour IV with inhaled anesthetics
Parkinson’s disease = acute dystonia
Codeine dose
Cough suppressant: 15 mg
Analgesia 60 mg
PO OR IM
NEVER IV → HISTMAINE INDUCED HYPOTENSION
Meperidine Post-op shivering dose
12.5 mg IV
Morphine intra-op dose
Intra Op: 1-10 mg IV
Hydromorphone intra -op dose
Intra Op: 1-4 mg
**Give 0.5 mg intermittently!
HAVE TO REDOSE Q 4 HOURS
Alfentanil Dose induction
Induction Laryngoscopy: 15-30 µg/kg IV
**give 90 sec prior
Induction alone: 150-300 µg/kg IV
Alfentanil Maintenance Dose
Maitenance: 25-150 µg/kg/hour w/ inhaled gas
Alfentanil MAC considerations
Alfentanil = up to 70% ↓ in MAC
Fentanyl Induction dose
1.5 - 3 𝝻g/ kg IV
**give 5 mins prior
Fentanyl Other doses
Analgesia: 1-2 𝝻g/kg IV
Adjunct with inhaled gases: 2-20 µg/kg IV
Surgical Anesthesia:(solo): 50-150 µg/kg
Transdermal: 75-100 µg (18 hr steady state delivery
Transmucosal (oral): 5-20 µg/kg
Peds 2-8 yo: 15-20 µg/kg PO 45 min prior
***1 mg PO Fentanyl=5 mg PO morphine
Remifentanil Induction dose
0.5 - 1 µg/kg over 1 min
DOSE IN IBW
Remifentanil maintenance dose
Maitenance: 0.25-1 µg/kg n IV OR 0.25 to 1 µg/kg IV or 0.005 to 2 µg/kg/min IV
*** before stopping give longer acting opioid
Not recommended for spinal or epidural use
Sufentanil Induction dose
18.9 µg/kg IV
Sufentanil Analgesia dose
Analgesia: 0.1-0.4 µg/kg IV
Fentanyl MAC
Fentanyl 3 µg/kg IV 25-30 min before surgical incision = ↓ MAC of ISO or DES to 50%
Sufentanil and MAC
Sufentanil decreases MAC with Enflurane by 70 to 90%
50 to 91% decrease
Alfentanyl and MAC
Alfentanyl = up to 70% decrease in MAC
Remifentanyl and MAC
50 to 91% decrease
Onset of Remifentanyl, surentanil , and fentanyl
30-60 sec
Onset of Alfentanil
1.4 min
Onset of Hydromorphone and Meperidine
5-15 min
Onset of morphine
10-20 min
Morphine Peak
IM: 45-90
IV: 15-30 minutes
Duration of Hydromorphone and Meperidine
2-4 hrs
Duration of morphine
4-5 hours
Duration of Fentanyl
1-1.5hr
Duration of Remifentanyl
6-8 min
PK / % nonionized (pH 7.4) - Meperidine
8.5/7%
PK / % nonionized (pH 7.4) - Morphine
7.9/ 23%
PK / % nonionized (pH 7.4) -
hydromorphone
Less hydrophilic than morphine
PK / % nonionized (pH 7.4) -
Alfentanil
6.5/ 89%
PK / % nonionized (pH 7.4) - Fentanyl
8.4/8.5%
VERY lipid soluble
PK / % nonionized (pH 7.4) - Remi
7.3/ 58%
PK / % nonionized (pH 7.4) - Sufent
8.0/20%
Very lipid soluble
Meperidine Vd/ part Co
305 Vd / 32 part co
Morphine Vd
224 Vd/ 1 part co
accumulates rapidly in kidneys, liver and skeletal muscles
Alfentinil Vd
27 L
Fentanyl Vd
335 L
LARGE Vd - largest it seems
IV (<5 mins 80% is gone)
->highly vascular tissues
-> inactive tissue sites
Remifent Vd
30 L
sufent Vd
123 L
Larger Vd than alfentanil
Protein Binding Meperidine
60%
Protein Binding Morphine
35%
Protein Binding Alfentanil
92 % Binds to α1- acid glycoprotein
Protien Binding Fentanyl
84%
Protein binding Remifent
66-93%
Protien Binding Sufent
92.5% to α1- acid glycoprotein
Metabolism Liver/hepatic
codiene, sufentanil, meperidine 90%
Metabolism Morphine
Glucoronic acid conjugation
metabolites:
Morphine -3 glucorinide (75-95%) INACTIVE
Morphine -6-glucoride: ACTIVE
Causes the late ventilatory depression
Metabolism of Alfentanil & Fentanyl
CYP3A4
Metabolism of Remifentanil
Hydrolysis by plasma and tissue esterases
allows for brief action, rapid onset and offset, lack of accumulation and rapid recovery when discontinued.
SIMILAR TO PROPOFOL AND KETAMINE
Meperidine Metabolite
Normeperidine
Does Hydromorphone have an active metabolite
Yes
Metabolite of Alfentanil
Noralfentanil
Metabolite of Fentanyl
Norfentanyl
Effect site equilibration time (blood/brain)- alfentanil
1.4 minutes
Effect site equilibration time (blood/brain)- fentanyl
6.8 min
Effect site equilibration time (blood/brain)- Remifent
1.1 min
Effect site equilibration time (blood/brain)- sufentanil
6.2 min
1/2 time for codeine
3-3.5 hrs
1/2 time for meperidine
3-5 hrs
**35 hrs with Renal failure
1/2 time for morphine
1.5-3.5 hrs
1/2 time for alfentanil
**cirrhosis prolongs E 1/2 time
1/2 time for Remifent
6.3 minutes (99.8%)
clearance for meperidine
1.02 L/min
Renal (acidic urine can speed up elimination)
clearance for morphine
1.05 L/min
clearance for fentanyl
Kidneys
clearance for Remifent
kidneys (unaffected by renal or liver dx)
3L/min
**8x faster than alfentanil
clearance for sufentanil
renal and fecal
***Caution with chronic renal failure
First pass meperidine
Hepatic 80%
First pass morphine
25% for PO,
NONE in lungs
first pass for fentanyl
75% in lungs
first pass for sufentanil
60% LUNG
Context sensitive half time alfentanil
60 min
Context sensitive half time fentanyl
260 min
Greater than sufentanil (d/t inactive tissue accumulation, will return to plasma and replace what has been metabolized)
Context sensitive half time remifentanil
4 min
Context sensitive half time sufent
30 min
“Shorter” - per castillo
CNS effects codeine
MINIMAL SEDATION
DIZZINESS
CNS effects meperidine
Sedation, Euphoria
SEROTONIN SYNDROME – careful with TCA’s and MAOI’s
CNS effects Morphine
Analgesia, euphoria, sedation and diminished ability to concentrate
CNS effects Fentanyl
‣Seizure like activity on SSEP and EEG with doses > 30 µg/kg IV
‣ ↑ ICP (6-9 mmHg)
CNS effects Remifent
‣Seizure-like activity
CV effects meperidine
Tachycardia, (-) inotropic
CV effects morphine
Histamine release = ↓ BP
CV effects hydromorphone
NO HISTAMINE RELEASE
CV effects Fentanyl
‣ Depressed Carotid sinus barreceptor reflex = Bradycardia, ↓BP, ↓CO
NO histamine release
CV effects Remifent
‣↓ B/P and HR
CV effects Sufentanil
‣Bradycardia causes ↓CO
Pulmonary
Meperidine: Depression of ventilation
Remifent: ‣ Synergistic depression of ventilation with propofol
GI
They pretty much all cause NV except fro hydromorphone, fent, alfent, and sufent…
Remifent: does cause N/V
Other side Effects codeine:
PHYSICAL DEPENDENCE
Other Side effects meperidine:
TOXICITY: Delirium (confusion and hallucinations, myoclonus and seizures)
CROSSES PLACENTAL BARRIER!
Other side effects morphine:
feeling of body warmth,
heaviness of extremities,
dryness of the mouth,
and pruritus.
Side effects of fentanyl
SYNERGISM w/ Benzos and propofol
side effects with Remifent
Hyperalgesia d/t previous acute exposure to large opioid doses and tolerance.
Side effects with Sufent
CHEST WALL AND ABDOMINAL MUSCLE RIGIDITY.
Clinical considerations with morphine
Caution with use in renal and elderly patients. Metabolites stick around longer in renal
Serum plasma concentrations increase with age.
Women > men: analgesic potency and slower speed of offset
Consideration for Alfentanil
USE IN PARKINSON’S = ACUTE DYSTONIA
Other
Analogues: Fentanyl, Sufentanil, Alfentanil and Remifentanil
Withdrawal onset 2-6 hrs (faster than morphine)
Chart
What blocks pain at the Brain? Perception
opioid, a2 agonists, general anesthetics
What blocks at the spinal cord? Modulation of afferent signals in the dorsal horn of spinal cord and production of reflex reaction
Local anesthetics, opioids, Ketamine, a2 agonists
What blocks pain transmission of action potential via A(delta) and C fibers
Local anesthetics
What blocks pain at Peripheral nociceptors (Transduction of mechanical, chemical and thermal stimuli into an action potential)
Local anesthetics, NSAIDs
Unmyelinated C- fiber:
burning pain from heat and pressure from sustained pressure.
Myelinated A-fiber:
Type I fibers ( Aβ & Aδ fibers): heat, mechanical, chemical
Type II fibers (Aδ fibers): heat
Sensitization
Sensitization- hurts more over time.. Lowers threshold
Secondary Hyperalgesia:
uninjured skin surrounding the injury (only from mechanical stimuli).
Sensitization of central neuronal circuits
Primary Hyperalgesia: at the original site of injury from heat and mechanical injury.
Decreased pain threshold
Increased response to suprathreshold stimuli
Spontaneous pain
Expansion of receptive field
Laminae III & IV:
NKI receptor with substance P
Lamina II
(substantia gelatinosa [opioids]): afferent C Fibers
Periaqueductal gray -rostral ventromedial medulla (PAG-RVM) system
Depress or facilitate the integration of pain info in the spinal dorsal horn.
Excitatory impulses
Glutamate
Calcitonin
Neuropeptide Y
Aspartate
Substance P
Inhibitory impulses
GABA
glycine
enkephalins
norepinephrine
dopamine
Spinothalamic
Pain, temperature, and itch (Laminae I, VII, & VIII: All afferent fibers)
Spinobulbar -cerebellum
Behavior toward pain (Laminae I, V, & VII)
Spinohypothalamic
Autonomic, neuroendocrine, and emotional aspects of pain (Laminae I, V, VII, & X)
Where is S1 and S2
Forebrain
Most of modulation of pain happens at forebrain or somatosensory cortex
Hyperpolarize A-delta and C fibers
Decrease release of substance P
Opening of K+ channels/inhibition of Ca++ channels
Neuropathic pain
Persists after the tissue has healed -> allodynia and hyperalgesia
Increased risk: Cancer patients d/t chemo and radiation therapy
Treatment: symptomatic (opioids gabapentin, amitryptiline, cannabis)
PAG-RVM system:
µ, κ, δ opioid receptors
hyperalgesia & Allodynia
When do neonates have pain perception
23 weeks of gestation