Opioid analgesic

1. OPIOID ANALGESICS
 Pain or analgesia is an unpleasant sensation
 Pain is a warning signal and indicates that there is some
impairment in the body.
 Somatic pain: pain arising from the skin and integumental
structures, muscles, bones and joints. Usually caused by
inflammation.
 Visceral pain: pain arising from viscera. May be
accompanied by autonomic responses like sweating, nausea
and hypotension
 Referred pain: when pain is referred to cutaneous area
which receives nerve supply from the same spinal segment
as that of the affected viscera.

2.  Analgesic is a drug that relieves pain without loss of
consciousness. They only offer sympathomimetic relief
without affecting the cause.
 Two types:
 Opioid or morphine type of analgesics.
 Non-opioid or aspirin type of analgesics.
 Opium is a dark brown gummy substance obtained
from Papaver somniferum.
 On incising the unripe seed capsules, a milky juice
comes out which turns brown on drying and this is
crude opium.

3.  It was used both for medicinal and recreational purposes
as it causes euphoria.
 By 19th century, pure opium alkaloids were available for
therapeutic use.
 But because they were equally abused, efforts were made
to isolate the analgesic property, i.e. to obtain an opioid
that is only analgesic and has no euphoric effects.
 Opioid is the term used for drugs with morphine-like
actions. They were earlier called as narcotic analgesics.
 It is found that there are 3 families of endogenous opioid
peptides released in the body viz enkephalins,
endorphins and dynorphins.
 This indicates that we have a natural system in the body
that releases various opioid peptides in response to pain.

4. CLASSIFICATION: (depending on action)
 Agonists:
 Natural: morphine, codeine
 Synthetic: pethidine, methadone
 Antagonists:
 Naloxone
 Naltrexone
 Mixed agonist-antagonists:
 Pentazocine
 nalorphine

5. CLASSIFICATION: (depending on source)
 Natural:
 Morphine
 Codeine.
 Semisynthetic:
 Heroin
 Oxymorphone
 Synthetic:
 Pethidine
 fentanyl

6. MORPHINE: (agonist-natural)
 It is the most important alkaloid of opium.
 Acute morphine poisoning may be accidental,
suicidal or homicidal.
MOA:
 morphine and other opioids produce their effects
by acting on opioid receptors.
 These receptors are abundant in CNS and other
tissues.
 Opioid receptors are mu (μ) kappa (κ) and delta
(δ)

7. PHARMACOLOGICAL ACTIONS:
 Central nervous system: analgesia, euphoria, sedation,
hypnosis, respiration, cough center, nausea, emesis,
heat regulation, excitatory effect
 Cardiovascular system: hypotension (direct peripheral
vasodilation)
 Gastric and gut mobility is decreased.
 Delays digestion of food in small intestine by reducing
intestinal secretions.
 Tone of contractions of ureter and volume of urinary
bladder is increased.

8. ADVERSE EFFECTS:
 Nausea, vomiting, dizziness, mental clouding,
respiratory depression, constipation, dysphoria,
urinary retention and hypotension.
 Repeated administration of morphine results in
development of tolerance to some of its effects.
 Opioids produce both psychological and physical
dependence.
MANAGEMENT OF ADDICTION:
 Morphine is slowly withdrawn over several days and
oral methadone is given.

9. USES:
 Used as analgesic, preanaesthetic medication,
diarrhoea, acute left ventricular failure, cough, special
anasthesia, sedative.
PRECAUTIONS AND CONTRAINDICATIONS:
 Avoid opioids in patients with COPD.
 Not to be used in case of head injury.
 Avoid in decreased BP as morphine may further
decrease.
 Not recommended in combination with CNS
depressants.

10. PETHIDINE: (agonist-synthetic)
 It is a derivative of morphine.
 Many of its actions resembles to that of morphine.
 Pethidine 1/10th as potent as morphine.
 As an analgesic, pethidine is equal to morphine.
 Onset of action is more rapid and duration of action is
shorter.
 Adverse effects are similar to morphine (except
constipation and urinary retention)
 Fentanyl, methadone are derivatives of pethidine.

11. NALOXONE: (antagonists)
 Acts as a competitive antagonist to all types of opioid
receptors.
 In normal individuals, it does not produce significant
actions. But in opium addicts, given IV it promptly
antagonises all the actions of morphine.
 It also blocks the action of endogenous opioid
peptides- endorphins, enkephalins and dynorphins
 It blocks the analgesia produced by placebo and
acupuncture.
 Used in morphine over dose, diagnosis of opioid
dependance.

12. PENTAZOCINE: (mixed agonists and antagonists)
 It was developed to reduce the addiction and adverse
effects of an analgesic.
 Pentazocine is a κ receptor agonist.
 CNS effects of pentazocine are similar to morphine.
Euphoria is seen only in lower doses.
 Sedation and respiratory depression is less.
ADVERSE EFFECTS:
 Sedation, sweating, dizziness, nausea, nightmares,
hallucinations.