Analgesics are drugs that selectively relieve pain by acting in the central nervous system or on peripheral mechanisms without affecting consciousness. There are two main types of analgesics: opioid analgesics (addictive) and non-opioid analgesics (non-addictive). Morphine is a potent opioid agonist derived from opium that acts on mu-opioid receptors in the central nervous system to produce analgesia, sedation, euphoria and respiratory depression. While highly effective at relieving pain, morphine can also cause side effects like nausea, vomiting, constipation, urinary retention and respiratory depression at high doses.

1. Analgesics
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Analgesics
Drugs that selectively relieve pain
by acting in central nervous
system or on peripheral
mechanisms without affecting
consciousness.
These relieve pain as a symptom
without altering its cause.

3.  These are NOT analgesics……
 Local anaesthetics relieve pain by
nonselective desensitisation of tissues
 Demulcents, protective or soothing effects
 Antacids, chemical neutralisation
 General anaesthetics, alter consciousness
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4. Types of analgesics:
 Opioid analgesics or narcotic or morphine
like analgesics (addictive)
 Non-opioid analgesics or non-narcotic or
aspirin like analgesics (Non addictive)
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Pain
An ill-defined, unpleasant sensation usually
evoked by an external or internal noxious
stimulus, signal for the injury or insult of
an area
A protective and diagnostic method
if not treated, becomes unbearable and starts
affecting normal body functioning.

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Types of pain
 Pricking, burning, itching pain
 Dull or sharp
 Superficial
 Visceral pain

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Mechanism of pain
 Painful stimuli
 Pain neurotransmitters
 Prostaglandins
 Pain receptors
 Pain perceiving neurons
 Inhibitory neurotransmitters

9. OPIOID ANALGESICS
 Very potent
 Induce analgesia by stimulation of central
opioid receptors.
 Induce sedation
 Primary use is to reduce the intensity of
pain and anxiety.
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10. OPIOID
 Any natural, semisynthetic or synthetic
substance that produces morphine like
effects by binding to opioid receptors.
OPIATE
 More restrictive to morphine like drugs
obtained from juice of opium poppy and
resembling structurally to morphine
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13. NARCOTICS
 Used to refer to opioid analgesic.
 In therapeutics, this term refers to drugs
that induce deep sleep
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14. OPIOID ANALGESICS
Divided into
 Opioid agonists
 Opioid mixed agonists, antagonist and
partial agonists
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15.  Most opioids are mu agonists with varying
activity on kappa receptors.
 Opioid receptors are 7 transmembrane
spanning proteins that are coupled to
inhibitory G-proteins.
 When activated, they decrease adenyl
cyclase production of the secondary
messenger cyclic adenosine
monophosphate.
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16.  This causes a decrease in calcium influx
from inhibition of voltage-gated calcium
channels and results in the activation of
potassium channels, which leads to
hyperpolarization. The hyperpolarized state
causes inhibition of neuronal signaling,
which in this case inhibits pain
transmission.
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17.  Opioids are classified into categories,
depending on receptor binding and affinity.
These classifications are agonist, partial
agonist, and antagonist. There are opioids
that have dual agonist and antagonist
functions.
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18. A. OPIOID AGONISTS:
 I. Natural opium alkaloids e.g. morphine
and codeine
 II. Semi-synthetic opioids e.g. heroin,
etorphine etc.
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19. III. Synthetic Opioids
 1. Phenylpiperidines: Pethidine, prodine
etc.
 2. Anilidopiperidines: Fentanyl,
sufentanil etc.
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20.  3. Diphenylpropylamine derivatives:
Methadone, Loperamide etc.
 4. Morphinans e.g. Levorphanol and
levomethorphan
 5. Benzomorphans e.g. Phenazocine
 6. Miscellaneous drugs: Tramadol, Tilidine
etc.
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21. B. Opioid mixed agonist-
antagonists and partial agonists
 I. Semi-synthetic opioids: e.g.
Buprenorphine and nalbuphine
 II. Synthetic opioids
 i. Benzomorphans e.g. Pentazocine and
cyclazocine
 ii. Morphinans e.g. Butorphanol.
 iii. Miscellaneous agents: Meptazinol
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22. Mechanism of Action:
 Morphine or other opioids interact with 4
families of opioid receptors
 These receptors are present on neurons in
CNS and peripheral tissues and are
designated by the Greek letters Mu (μ),
Kappa (κ), Delta and Sigma.
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23. Opioid agonist (Natural Opium
Alkaloids) e.g. Morphine
 Principal alkaloid of opium
 Morphine sulphate is the principal salt
 In 1804 by F. W. A. Serturner
 A standard against which the analgesic
potency and actions of other opioid
analgesics are compared.
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24. Pharmacological Effects: CNS
 Opioid receptor agonist and its main effect
is binding to and activating the μ-opioid
receptors in CNS (analgesia, sedation,
euphoria, physical dependence and
respiratory depression).
 Irregular and species specific
 Site specific depressant and stimulation
actions on CNS
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25. Analgesic action:
 Strong analgesic
 Fear, anxiety and autonomic effects
associated with pain are also depressed
 High doses can mitigate all types of pain
 Degree of analgesia increases with dose
 Does not affect touch, vision, hearing,
smell and consciousness.
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26. CNS depression/Sedation
 In all species, there is at least an initial
period of stimulation followed by
depression
 Morphine usually exhibits sedating and
calming effect in all species when they are
suffering from pain.
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27. Emetic Centre
 The emetic effect is a result of direct
stimulation of the CTZ
 Horses, ruminants and swine do not
respond to the emetic effect of morphine
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28. Cough Centre
 Morphine is an effective antitussive agent.
 Depresses cough centre that appears to be
more susceptible to morphine than other
medullary centres.
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29. Respiratory Centre
 Morphine is a potent resp. depressant.
 It depresses respiratory centre in a dose
dependent manner
 As the CNS depression increases,
respiration is also depressed
 It can also cause bronchoconstriction
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30. Spinal Cord
 Morphine exerts both stimulant and
depressant actions on the spinal cord
Other Central Effects:
Stimulation of vagal nucleus by morphine
produces parasympathetic responses like
slowing of heart, increased tone and
motility of GI tract, increased salivary and
bronchial secretions.
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31. Side/ Adverse effects:
 Pupil constriction
 Peripheral vasodilation
 Hypotension
 Vomiting
 Defecation followed by constipation
 Urinary retention
 Sweating
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32. Treatment
 In morphine toxicity, naloxone is the agent
of choice.
 Mechanical respiratory support is also
considered in cases of severe respiratory
depression.
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33. Drug Interactions
 CNS depressant effects can be enhanced
by barbiturates, inhalant anaesthetics,
antihistamines and phenothiazines
 Analgesic efficacy of morphine can be
potentiated by tricyclic antidepressants and
amphetamine.
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