OPIOID PHARMACOLOGY
PG Seminar
Dr. Rohan Kolla,
PG in MD PHARMACOLOGY,
JNMC, BELGAUM
Outline
•
•
•
•
•
•
•

Definitions
History
Endogenous Opioids
Opioid Receptors
Pharmacokinetics
Pharmacological Effect Pro...
Outline (contd.)
• Clinical Pharmacology
– Therapeutic use of Opiates in Pain control
– Guidelines for Opiate Dosing
– Non...
Etymology
• OPIOIDS ( from Greek opos, ‘juice’): is any
substance regardless of its origin or structure
that produces morp...
• Narcotic (from Greek narkos, ‘I benumb’):
– any substance which induces sleep
– any substance which acts on opioid recep...
Papaver somniferum
History
•
•
•
•
•

Oldest drug known to mankind
Sumer – 4000 BC
Greeks; Theophrastus – 3rd century BC
Arab Physicians
Used...
History (contd.)
• Opium Addiction – a lifestyle statement in 17th
– 18th century
• It was the source of an important "soc...
• East India company
• Opium Wars: 1/3rd of adult chinese population
was addicted
• India is a major produces of legal opi...
History (contd.)
• Frederick Sertuner 1806: isolated the
crystalline pure substance from opium that he
named morphine ( af...
Mapping of the morphinoids
• Huda Akil
• John Leibeskind, UCLA
• Stimulus Produced Analgesia
• Periaqueductal Grey matter
...
Mapping of the morphinoids

•Avram Goldstein, Stanford

•Grind and Bind technique
•Radiolabelled opioids
Receptors
• Solomon Snyder &
• Candace Pert, John Hopkins
• Grind and Bind technique
• Improved radiolabelling techniques
...
Substance X
• Hans Kosterlitz &
• John Hughes, Aberdeen University, Scotland

• Pig brain soup
• Guinea Pig Ileum
• Discov...
Endogenous Opioid Systems
• An agent found within the brain that acts through
an opioid receptor is called as an endogenou...
Endogenous Opioid Systems
• The distribution of cells producing these three
different types of endogenous opioids varies:
...
Functions of Endogenous Opioids
• Modulation of
pain perception
• Modulation of
Motor activity for
sustained periods
– “ru...
OPIOID RECEPTORS
• μ, κ and δ; the three opioid receptors
• Rhodopsin family of GPCRs
• Disributed through the brain & spi...
OPIOID RECEPTORS (contd.)
• Upon activation of the receptors , Gi/Gs
coupling occurs leading to a large no. of
intracellul...
Pharmacokinetics
Absorption
• Modestly absorbed through GI tract -oral,
rectal,
• Depends on lipophilicity
• High first pass metabolism
• M...
Distribution
• 1/3rd of morphine is plasma protein bound
• They achieve high concentrations in highly
perfused tissues – b...
Metabolism
• In liver
Morphine  morphine-6-glucuronide, morphine-3glucuronide
These have significant activity themselves....
Excretion
• In kidneys,
M6G & M3G are excreted by glomerular filtration.
CRF can cause elevated levels of these metabolite...
Pharmacodynamic effect
profile of Clinically Used
Opioids
Central Nervous System
effects
Analgesia
• When given to patients in pain:
less intense, tolerable and they feel more
comfortable with relief of distress...
Analgesia – Different pain states
• Acute nociception: activation of small
high threshhold sensory afferents, Aδ & C
fibre...
Analgesia – Different pain states
• Tissue Injury:
Ex: Burns,
abrasion, joint
inflammation,
musculoskelet
al injury
Analgesia – Different pain states
• Nerve Injury:
Activation of Aβ
Ex: Nerve
compression,
chemotherapy,
diabetes, etc
Analgesia – Mechanism
• Supraspinal
Action
Analgesia – Mechanism
• Spinal Opiate
Action
Analgesia - Mechanism
Peripheral Mechanism:
• Basic tenet of Opiate pharmacology has been
that these drugs act centrally
•...
Mood alterations & Rewarding
properties
• Pathways – Mesocorticolimbic Dopamine
system

Opiates increase DA release in the...
Mood
alterations &
Rewarding
properties
CNS depression – Respiration
• Respiratory depression: primary cause of morbidity
secondary to opioid therapy.
• All phase...
Effect on Cough
• Direct inhibitory effect on the cough centre of
medulla
• Without loss protective glottic function
• The...
Effect on Nausea & Emesis
• Direct stimulation of CTZ
• A vestibular component is also involved
• Apomorphine – a congener...
Seizure & Convulsions
Some opioids at a slightly higher doses can
produce epileptogenic activity
• Meperidine
• Frank seiz...
Other effects
• Temperature regulation: Slight fall in body
temperature
– In withdrawal, there will be rise

• Miosis: Par...
Peripheral effects
Neuroendocrine Effects
• Broadly Opioids block the release of many
hormones of the HPA axis.
A. Adrenal & sex steroid horm...
Neuroendocrine Effects
• endocrinopathies, Hypogonadotrophic
hypogonadism, decreased libido, menstrual
irregularities, eff...
Cardiovascular Effects
• Peripheral vasodilatation, reduced peripheral
resistance and inhibition of baroreceptor reflexes
...
Cardiovascular Effects – (contd.)
• This protective effect is partly mediated by
increase in the centrally mediated vagal
...
Effect on GI Tract
• Opioid receptors – dense distribution in the
enteric plexuses
• Stomach:
– delays gastric emptying
– ...
Effect on other smooth muscle
Ureter & Urinary Bladder
• Inhibition of urinary voiding reflex
• Increase in the tone of ex...
Effect on Immune system
• Opioid receptors are present on different cells
of the immune system like neutrophils, natural
k...
Clinical Pharmacology
Classification
• Receptor Affinity
A. Opioid Agonists: Morphine, Codeine,
Meperidine, Fentanyl, Methadone, Tramadol
B. Opi...
Pethidine (Meperidine)
• Potent MOR agonist
• Used in post op pain, chronic pain of severe
degree & post anesthetic shiver...
Levorphanol
•
•
•
•

Morphinian series
Agonist at MOR, DOR & KOR
T1/2 – 12 hours
Action & uses similar to morphine.
Loperamide & Diphenoxylate
•
•
•
•
•

Piperidine derivatives
Approved for treatment of diarrhoeas
It slows GI motility
Als...
Fentanyl & Its Congeners
• Fentanyl, Alfentanil, Sufentanil & remifentanil
• They are used as anesthetic adjuvants and
ind...
Fentanyl & Its Congeners
• Uses:
– Inducing agents especially in cardiovascular
operations – high dose fentanyl & sufentan...
Methadone
•
•
•
•

Long acting MOR agonist
Racemic mixture – L isomer is more potent
Similar to morphine but enhanced dura...
Tramadol
• Synthetic codeine analogue
• Weak MOR agonist
• Used in the treatment of mild to moderate
pain
• Epileptogenic
...
Pentazocine
• KOR agonist and a weak antagonist/partial
agonist at MOR receptors
• Effects similar to morphine – analgesia...
Nalbuphine

• KOR agonist with
competitive antagonistic
activity at MOR
• Analgesia is similar
• Respiratory depression
ex...
Buprenorphine
• Highly lipophilic partial agonist at MOR
• 20-50 times more affinity to MOR than
morphine
• Used in analge...
Opioid Antagonists
•
•
•
•
•

Nalorphine,
Naloxone,
Naltrexone,
Naltrindole,
Nalmefene
They have very little effect if giv...
Opioid Antagonists
Effect in the absence of Agonists
• Mild hyperalgesia
• Reverse the hypotension associated with
differe...
Opioid Antagonists
Effect in the presence of Agonists
• Effect on Acute opioid actions:
– Increase in respiratory rate & d...
Opioid Antagonists
Effect in the presence of Agonists
• Effect on Opioid dependant patients:
– Moderate to severe withdraw...
Opioid Antagonists - Uses
•
•
•
•

Acute toxicity /overdosage
Management of constipation
Management of abuse syndromes
Tra...
Centrally acting antitussives
• Codeine, hydrocodone & oxycodone
• Dextromethorphan:
– Analog of codeine
– Elevates the th...
Therapeutic Uses of OPIOIDS
Analgesia
• Most potent pain-relieving drugs available
• Adequate pain relief
• Many guideline...
Therapeutic Uses – Routes of administration

1.
2.
3.
4.
5.
6.
7.
8.

Patient controlled analgesia
Spinal Delivery
Local d...
Therapeutic Uses – Other uses
• Dyspnoea- Acute LVF & Acute
Pulmonary edema
– Pink puffers

•
•
•
•

Cough
Diarrhoea
Shive...
Contraindications & Cautions
• Use of pure agonists with weak partial
agonists
• Use in patients with head injuries
• Use ...
Toxicity, Tolerence & Dependence
Tolerance
• When large doses are given at short intervals
• Analgesia, sedation & respiratory depression
are the commonest...
PhysicalDependence
• Dependence refers to a state of adaptation
manifested by receptor/drug class-specific
withdrawal synd...
Psyschological Dependence
• Reason for opioid abuse:
– Euphoria, indifference to stimuli, sedation, abdominal
experiences ...
Toxicity & Overdosage
• Clinical overdosage, accidental
overdosage or suicidal
• Signs & symptoms:
– Triad of coma, pinpon...
Treatment of Opioid toxicity &
Overdosage
• Ventilatory support
• DOC – IV Naloxone 0.01mg/kg
• Treatment should be such t...
Screening Methods
Acute pain
•
1.
2.
•
1.
2.
•
1.
2.
3.
4.

MODELS USING THERMAL STIMULUS
Hot plate method
Tail –Flick method
MODELS USING E...
• MODELS USING MECHANICAL STIMULUS
1. Haffner’s tail clip method
2. Randall Selitto test
_________________________________...
Cancer pain
• Rat model of bone cancer pain
_____________________________________
In Vitro Methods
1. 3H-Naloxone binding ...
References
1. Essentials of Medical Pharmacological, K D. Tripathi,
6th ed
2. Pharmacology and Pharmacotherapeutics, R S.
...
References
8. Anatomy of a scientific Discovery, Jeff
Goldberg, Bantam Books.
Thank you!

“Religion is the opium of the masses.” –
Karl Marx
Mechanisms of tolerance
• Receptor disposition
• Adaptation of intracellular signalling
mechanisms in the opioid receptor ...
Structure Activity Relationship
• Message – Address concept
• Message: a protonated nitrogen, a phenolic
ring, a hydrophob...
Opioid pharmacology - A comprehensive subject seminar on Opioids
Opioid pharmacology - A comprehensive subject seminar on Opioids
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Opioid pharmacology - A comprehensive subject seminar on Opioids

  1. 1. OPIOID PHARMACOLOGY PG Seminar Dr. Rohan Kolla, PG in MD PHARMACOLOGY, JNMC, BELGAUM
  2. 2. Outline • • • • • • • Definitions History Endogenous Opioids Opioid Receptors Pharmacokinetics Pharmacological Effect Profile Classification of Opioids – Pure AGONISTS – Agonist-antagonists – Antagonists
  3. 3. Outline (contd.) • Clinical Pharmacology – Therapeutic use of Opiates in Pain control – Guidelines for Opiate Dosing – Non analgesic therapeutic uses – Acute Opioid toxicity • Screening Methods
  4. 4. Etymology • OPIOIDS ( from Greek opos, ‘juice’): is any substance regardless of its origin or structure that produces morphine-like effects that are blocked by antagonists such as nalaxone. • OPIATES: includes the natural alkaloids derived from the resin of the opium poppy; – some authors also include the semisynthetic substances derived directly from these alkaloids.
  5. 5. • Narcotic (from Greek narkos, ‘I benumb’): – any substance which induces sleep – any substance which acts on opioid receptors – any illicit substance – legally - opium, opium derivatives & their semisynthetic derivatives
  6. 6. Papaver somniferum
  7. 7. History • • • • • Oldest drug known to mankind Sumer – 4000 BC Greeks; Theophrastus – 3rd century BC Arab Physicians Used for – asthma, bad eyesight, diarrhoea and as a euphoriant.
  8. 8. History (contd.) • Opium Addiction – a lifestyle statement in 17th – 18th century • It was the source of an important "social problem", one of the first "public health" concerns, known as "baby-doping" (giving a child opium to keep them quiet).
  9. 9. • East India company • Opium Wars: 1/3rd of adult chinese population was addicted • India is a major produces of legal opium • Taliban & the Afghan War
  10. 10. History (contd.) • Frederick Sertuner 1806: isolated the crystalline pure substance from opium that he named morphine ( after morpheus, the Greek god of dreams. • Arnold Beckett in 1950: Proposed that morphine like compounds act by binding to specific receptors in the brain
  11. 11. Mapping of the morphinoids • Huda Akil • John Leibeskind, UCLA • Stimulus Produced Analgesia • Periaqueductal Grey matter • Reversed by antagonists
  12. 12. Mapping of the morphinoids •Avram Goldstein, Stanford •Grind and Bind technique •Radiolabelled opioids
  13. 13. Receptors • Solomon Snyder & • Candace Pert, John Hopkins • Grind and Bind technique • Improved radiolabelling techniques • Discovery of Mu receptors in 1973
  14. 14. Substance X • Hans Kosterlitz & • John Hughes, Aberdeen University, Scotland • Pig brain soup • Guinea Pig Ileum • Discovery of ENKEPHALINS in 1973
  15. 15. Endogenous Opioid Systems • An agent found within the brain that acts through an opioid receptor is called as an endogenous opioid. • Principally three classes – enkephalins, endorphins, dynorphins • All are peptides derived from distinct large precursor proteins - POMC, preproenkephalin, preprodynorphin • Common amino terminal sequence: TYR-GLY-GLYPHE-(MET OR LEU)
  16. 16. Endogenous Opioid Systems • The distribution of cells producing these three different types of endogenous opioids varies: – limited to arcuate nucleus and hippocampus in case of POMC – in the areas of brain related to pain producing pathways in case of preproenkephalins – Wider distribution in case of preprodynorphins • ENDOMORPHINS – newly discovered endogenous opioids with atypical structures and selectivity towards μ receptors
  17. 17. Functions of Endogenous Opioids • Modulation of pain perception • Modulation of Motor activity for sustained periods – “runners high” • Autonomic regulation “When I’m tired, I go for a run and feel I have more energy when I’m done.”
  18. 18. OPIOID RECEPTORS • μ, κ and δ; the three opioid receptors • Rhodopsin family of GPCRs • Disributed through the brain & spinal cord; and also outside the CNS – vascular tissues, cardia, airway/lung, gut and cells of the immune system. • IUPHAR – MOP, KOP & DOP • Opiate receptor-like protein (ORL1 or NOP) with an endogenous ligand ‘nociceptin/orphanin(F/Q)’
  19. 19. OPIOID RECEPTORS (contd.) • Upon activation of the receptors , Gi/Gs coupling occurs leading to a large no. of intracellular events: – Inhibition of adenylyl cyclase activity – Reduced opening of voltage-gated Ca2+ channels – Stimulation of K+ current through GIRKs (G protein-activated inwardly rectifying K+ channels) – Activation of PKC & PLCβ
  20. 20. Pharmacokinetics
  21. 21. Absorption • Modestly absorbed through GI tract -oral, rectal, • Depends on lipophilicity • High first pass metabolism • Morphine - ~25% bioavailability by oral route • Codeine & oxycodone – low FPM • Well absorbed through SC & IM routes • Nasal Insufflation – rapid rise in blood levels
  22. 22. Distribution • 1/3rd of morphine is plasma protein bound • They achieve high concentrations in highly perfused tissues – brain, liver, kidneys & spleen • In chronic administration – this buildup can take place & opioids are found in the plasma long after their dosage has been stopped
  23. 23. Metabolism • In liver Morphine  morphine-6-glucuronide, morphine-3glucuronide These have significant activity themselves. • CYP3A4 & CYP2D6 are involved in biotransformation of morphine congeners like heroin, codeine, fentanyl etc Ex: Increased & Decreased activity of CYP2D6
  24. 24. Excretion • In kidneys, M6G & M3G are excreted by glomerular filtration. CRF can cause elevated levels of these metabolites & lead to adverse effects – seizures, CNS depression
  25. 25. Pharmacodynamic effect profile of Clinically Used Opioids
  26. 26. Central Nervous System effects
  27. 27. Analgesia • When given to patients in pain: less intense, tolerable and they feel more comfortable with relief of distress • When given to normal patients: frankly unpleasant with drowsiness, difficulty in mentation, lessened physical activity and apathy
  28. 28. Analgesia – Different pain states • Acute nociception: activation of small high threshhold sensory afferents, Aδ & C fibres  Spinothalamic tracts anterior cingulate cortex ( limbic system). • Examples: hot plates, needle prick, incisions
  29. 29. Analgesia – Different pain states • Tissue Injury: Ex: Burns, abrasion, joint inflammation, musculoskelet al injury
  30. 30. Analgesia – Different pain states • Nerve Injury: Activation of Aβ Ex: Nerve compression, chemotherapy, diabetes, etc
  31. 31. Analgesia – Mechanism • Supraspinal Action
  32. 32. Analgesia – Mechanism • Spinal Opiate Action
  33. 33. Analgesia - Mechanism Peripheral Mechanism: • Basic tenet of Opiate pharmacology has been that these drugs act centrally • Recently, in conditions of inflammation it has been found that opioids act directly even on the peripheral terminals of small primary afferents.
  34. 34. Mood alterations & Rewarding properties • Pathways – Mesocorticolimbic Dopamine system Opiates increase DA release in the Nucleus Accumbens.
  35. 35. Mood alterations & Rewarding properties
  36. 36. CNS depression – Respiration • Respiratory depression: primary cause of morbidity secondary to opioid therapy. • All phases of respiratory activity – rate, minute volume, tidal exchange;  aperiodic & irregular breathing 1. Direct depression of rhythm generation in ventrolateral medulla 2. Desensitization of brainstem chemoreceptors which normally respond to rising PCO 2 3. Also desensitize the carotid & aortic chemosensors which usually respond to hypoxia.
  37. 37. Effect on Cough • Direct inhibitory effect on the cough centre of medulla • Without loss protective glottic function • There is no relation between the suppression of cough & respiratory depression. • Centrally acting antitussives – dextromethorphan, codeine, pholcodeine
  38. 38. Effect on Nausea & Emesis • Direct stimulation of CTZ • A vestibular component is also involved • Apomorphine – a congener of morphine is highly emetic but has no action on opioid receptors • 5HT3 receptor antagonists are used for opioid induced nausea & vomiting
  39. 39. Seizure & Convulsions Some opioids at a slightly higher doses can produce epileptogenic activity • Meperidine • Frank seizures & myoclonus • Several mechanisms – Inhibition of inhibitory interneurons – Direct stimulatory effects – Actions mediated by non-opioid receptors by their metabolites
  40. 40. Other effects • Temperature regulation: Slight fall in body temperature – In withdrawal, there will be rise • Miosis: Parasympathetic pathways by inhibition of GABAergic transmission – very last action to develop tolerance • Motor tone: high doses increase the muscle tone  chest wall rigidity, increased propensity to myoclonus
  41. 41. Peripheral effects
  42. 42. Neuroendocrine Effects • Broadly Opioids block the release of many hormones of the HPA axis. A. Adrenal & sex steroid hormones: general decrease in the release of testosterone, DHEA, cortisol and also the gonadotrophins from the pituitary – Direct effect on pituicytes & also a indirect effect on hypothalamic neurons  decreased releasing hormones
  43. 43. Neuroendocrine Effects • endocrinopathies, Hypogonadotrophic hypogonadism, decreased libido, menstrual irregularities, effect on secondary sexual characteristics! B. Prolactin: increased secretion due to loss of inhibitory control of dopamine C. Oxytocin & Vasopressin: KOR agonists inhibit the release of both the hormones
  44. 44. Cardiovascular Effects • Peripheral vasodilatation, reduced peripheral resistance and inhibition of baroreceptor reflexes – orthostatic hypotension – histamine release – Blunting of reflex vasoconstriction in response to PCO2 • Coronary Artery Disease: – Decreasing preload, inotropy and chronotropy – Decrease in O2 consumption, left ventricular enddiastolic volume & cardiac work
  45. 45. Cardiovascular Effects – (contd.) • This protective effect is partly mediated by increase in the centrally mediated vagal outflow. • Can aggravate hypovolemic shock • Respiratory depression  CO2 retention  cerebral vasodilatation  increase in ICT • Can be arrhythmogenic
  46. 46. Effect on GI Tract • Opioid receptors – dense distribution in the enteric plexuses • Stomach: – delays gastric emptying – also decreases the secretion of HCl • Intestine: – diminishes propulsive activity in both SI & LI – Intestinal secretions are reduced by inhibitpry effects on secretomotor neurons
  47. 47. Effect on other smooth muscle Ureter & Urinary Bladder • Inhibition of urinary voiding reflex • Increase in the tone of external sphincter  increase in the volume of the bladder Uterus • Restores the tone of hyperactive bladder secondary to oxytocics Biliary Tract • Sphincter of Oddi contracts – hence some pts with biliary colic will experience more pain when morphine is given
  48. 48. Effect on Immune system • Opioid receptors are present on different cells of the immune system like neutrophils, natural killer cells – direct modulation of their function • Suppression of HPA axis • In toto, the appear to suppress the immune function, but in the presence of pain syndromes they appear to improve immunity!!
  49. 49. Clinical Pharmacology
  50. 50. Classification • Receptor Affinity A. Opioid Agonists: Morphine, Codeine, Meperidine, Fentanyl, Methadone, Tramadol B. Opioid Agonist/Antagonist & Partial Agonist: Pentazocine, Nalbuphine, Butorphanol, Buprenorphine C. Opioid Antagoinists: Nalorphine, Naloxone, Naltrexone, Naltrindole, Nalmefene,
  51. 51. Pethidine (Meperidine) • Potent MOR agonist • Used in post op pain, chronic pain of severe degree & post anesthetic shivering • Its metabolite normeperidine is epileptogenic • It can block neuronal uptake of 5HT3 – can cause serotonin syndrome if used with MAO inhibitors & SSRIs • Concurrent use of Antihistaminics & TCAs can cause additive CNS depression
  52. 52. Levorphanol • • • • Morphinian series Agonist at MOR, DOR & KOR T1/2 – 12 hours Action & uses similar to morphine.
  53. 53. Loperamide & Diphenoxylate • • • • • Piperidine derivatives Approved for treatment of diarrhoeas It slows GI motility Also may act by decreasing secretions Loperamide has very less central effects because of the activity of P-glycoprotein • Diphenoxylate is available in FDC with atropine
  54. 54. Fentanyl & Its Congeners • Fentanyl, Alfentanil, Sufentanil & remifentanil • They are used as anesthetic adjuvants and inducing agents • Short ‘time to peak’ analgesic effect • Rapid termination of effect if used in bolus • MAC-sparing effect on gaseous anesthetics • Can cause muscle rigidity • But very minimal effect on myocardial parameters
  55. 55. Fentanyl & Its Congeners • Uses: – Inducing agents especially in cardiovascular operations – high dose fentanyl & sufentanil – Short procedures – remifentanil – Chronic analgesia – epidural – Cancer pain – transdermal patches
  56. 56. Methadone • • • • Long acting MOR agonist Racemic mixture – L isomer is more potent Similar to morphine but enhanced duration Can cause prolongation of QT interval –series cardiac arrhythmias Propoxyphene: Similar to methadone
  57. 57. Tramadol • Synthetic codeine analogue • Weak MOR agonist • Used in the treatment of mild to moderate pain • Epileptogenic Tapentadol
  58. 58. Pentazocine • KOR agonist and a weak antagonist/partial agonist at MOR receptors • Effects similar to morphine – analgesia, sedation, respiratory depression. • At high doses – dysphoric & psychotomimetic effects • Tachycardia & increase in BP • Can precipitate withdrawal in morphine dependant patients
  59. 59. Nalbuphine • KOR agonist with competitive antagonistic activity at MOR • Analgesia is similar • Respiratory depression exhibits ceiling effect – so relatively safe drug Butorphanol • Morphinian compound • Similar to Nalbuphine
  60. 60. Buprenorphine • Highly lipophilic partial agonist at MOR • 20-50 times more affinity to MOR than morphine • Used in analgesia & management of Opioid dependence
  61. 61. Opioid Antagonists • • • • • Nalorphine, Naloxone, Naltrexone, Naltrindole, Nalmefene They have very little effect if given alone. They produce their effects only when given with agonists or in some cases the endogenous opioid system is activated
  62. 62. Opioid Antagonists Effect in the absence of Agonists • Mild hyperalgesia • Reverse the hypotension associated with different forms of shock to some extent • Mild dysphoria • Neuroendocrine effects
  63. 63. Opioid Antagonists Effect in the presence of Agonists • Effect on Acute opioid actions: – Increase in respiratory rate & depth – Reversal of dysphoric & psychotomimetic effects – Overshoot phenomenon – Rebound release of catecholamines  tachycardia, hypertension, ventricular arrhythmias
  64. 64. Opioid Antagonists Effect in the presence of Agonists • Effect on Opioid dependant patients: – Moderate to severe withdrawal – Depends on the dose of the antagonist and also on the degree and duration of dependence – Methylnaltrexone & Alvimopan can reverse the GI effects of opioid dependence without pptting central withdrawal syndrome.
  65. 65. Opioid Antagonists - Uses • • • • Acute toxicity /overdosage Management of constipation Management of abuse syndromes Trauma – shock, stroke, brain trauma
  66. 66. Centrally acting antitussives • Codeine, hydrocodone & oxycodone • Dextromethorphan: – Analog of codeine – Elevates the threshold of – Fewer subjective & GI side effects • Pentoxyverine & Caramiphen
  67. 67. Therapeutic Uses of OPIOIDS Analgesia • Most potent pain-relieving drugs available • Adequate pain relief • Many guidelines are available – WHO, American pain Society, Federation of State medical board
  68. 68. Therapeutic Uses – Routes of administration 1. 2. 3. 4. 5. 6. 7. 8. Patient controlled analgesia Spinal Delivery Local drug action Rectal administration Inhalation Oral transmucosal administration Transnasal Administration Transdermal & Iontophoretic Administration
  69. 69. Therapeutic Uses – Other uses • Dyspnoea- Acute LVF & Acute Pulmonary edema – Pink puffers • • • • Cough Diarrhoea Shivering Anaesthetic adjuvants
  70. 70. Contraindications & Cautions • Use of pure agonists with weak partial agonists • Use in patients with head injuries • Use in pregnancy • Use in impaired pulmonary reserve • Use in patients with impaired hepatic &/or renal function • Use in patients with endocrine disease
  71. 71. Toxicity, Tolerence & Dependence
  72. 72. Tolerance • When large doses are given at short intervals • Analgesia, sedation & respiratory depression are the commonest effects to develop tolerance • Respiratory depression  60mg & 200mg • Tolerance does not develop to miotic, convulsant & constipatory effects • Cross tolerance – partial & incomplete  opioid rotation
  73. 73. PhysicalDependence • Dependence refers to a state of adaptation manifested by receptor/drug class-specific withdrawal syndrome produced by cessation of drug exposure. • Signs & symptoms – rhinorrhoea, yawning, chills, piloerection, hyperventilation, hyperthermia, diarrhoea, hostility & anxiety • Antagonist precipitated withdrawal
  74. 74. Psyschological Dependence • Reason for opioid abuse: – Euphoria, indifference to stimuli, sedation, abdominal experiences similar to intense orgasm – Reinforced by physical dependance • Therapy: – – – – – Methadone Clonidine Transcutaneous electrical stimulation Buprenorphine Naltrexone
  75. 75. Toxicity & Overdosage • Clinical overdosage, accidental overdosage or suicidal • Signs & symptoms: – Triad of coma, pinpont pupils & depressed respiration – Anuria, frank convulsions in children – Noncardiogenic pulmonary edema
  76. 76. Treatment of Opioid toxicity & Overdosage • Ventilatory support • DOC – IV Naloxone 0.01mg/kg • Treatment should be such that reversal should occur without precipitation of withdrawal • If the poisoning is due to methadone the pts may slip back into coma as antagonist have short half lives
  77. 77. Screening Methods
  78. 78. Acute pain • 1. 2. • 1. 2. • 1. 2. 3. 4. MODELS USING THERMAL STIMULUS Hot plate method Tail –Flick method MODELS USING ELECTRICAL STIMULUS Tooth pulp test Monkey shock titration test MODELS USING CHEMICAL STIMULUS Formalin test Writhing test Rat sigmoid colon model Inflammatory uterine pain model
  79. 79. • MODELS USING MECHANICAL STIMULUS 1. Haffner’s tail clip method 2. Randall Selitto test _______________________________________ Chronic pain 1. Neuropathic pain models 2. Vincristine-induced Neuropathy model 3. Diabetic neuropathy model 4. Persistent postthoracotomy pain model 5. Rat model of incisional pain
  80. 80. Cancer pain • Rat model of bone cancer pain _____________________________________ In Vitro Methods 1. 3H-Naloxone binding assay 2. µ Opiate receptor binding assay 3. Assay to study cannabinoids activity
  81. 81. References 1. Essentials of Medical Pharmacological, K D. Tripathi, 6th ed 2. Pharmacology and Pharmacotherapeutics, R S. Satoskar, S D. Bhandarkar, Nirmala N. Rege, 21st ed. 3. Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 12th ed 4. Rang & Dale’s Pharmacology 6th ed, 5. Basic & Clinical Pharmacology, Katzung’s, 11th ed. 6. Principles of Pharmacology: The Pathophysiologic Basis of Drug Therapy, Golan, LippinCott’s 7. Harrison’s Principles of Internal Medicine, 17th ed.
  82. 82. References 8. Anatomy of a scientific Discovery, Jeff Goldberg, Bantam Books.
  83. 83. Thank you! “Religion is the opium of the masses.” – Karl Marx
  84. 84. Mechanisms of tolerance • Receptor disposition • Adaptation of intracellular signalling mechanisms in the opioid receptor bearing neurons • System level counteradaptation • Fractional occupancy requirements
  85. 85. Structure Activity Relationship • Message – Address concept • Message: a protonated nitrogen, a phenolic ring, a hydrophobic domain.

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