Opioid Analgesics

1. ANSUMAN SAHU
OPIOID ANALGESICS

2. Algesia (pain) is an ill-defined, unpleasant
sensation, usually evoked by an external or
internal noxious stimulus.
Analgesic - A drug that selectively relieves pain by
acting in the CNS or on peripheral pain
mechanisms, without significantly altering
consciousness.

3. OPIOID ANALGESICS :
Opium A dark brown, resinous material obtained
from poppy (Papaver somniferum) capsule.
It contains two types of alkaloids.
 Phenanthrene derivatives
Ex - Morphine (10% in opium)
Codeine (0.5% in opium)
Thebaine (0.2% in opium), (Nonanalgesic)
 Benzoisoquinoline derivatives
Ex - Papaverine (1%) Nonanalgesic
Noscapine (6%)

4. CLASSIFICATION OF OPIOIDS :
1. Natural opium alkaloids: Morphine, Codeine
2. Semisynthetic opiates: Diacetylmorphine
(Heroin), Pholcodeine.
Many others like—Hydromorphone,
Oxymorphone, Hydrocodone, Oxycodone, are not
used in India.
3. Synthetic opioids: Pethidine (Meperidine),
Fentanyl, Methadone, Dextropropoxyphene,
Tramadol.

5. MORPHINE :
Morphine is the principal alkaloid in opium and still widely
used.
PHARMACOLOGICAL ACTIONS :
1. CNS
(a) Analgesia : Morphine is a strong analgesic. Though
dull, poorly localized visceral pain is relieved better than
sharply defined somatic pain; higher doses can mitigate
even severe pain—degree of analgesia increasing with
dose.
(b) Sedation
(c) Mood and subjective effects : Morphine has a
calming effect; there is loss of apprehension, feeling of
detachment, lack of initiative, limbs feel heavy and body
warm, mental clouding and inability to concentrate
occurs.

6. (d) Respiratory centre : Morphine depresses
respiratory centre in a dose dependent manner
(e) Cough centre : It is depressed; more sensitive
to morphine than respiratory centre.
(f) Temperature regulating centre : It is
depressed; hypothermia occurs in cold
surroundings.
(g) Vasomotor centre : It is depressed at higher
doses and contributes to the fall in BP.
2. Neuro-endocrine Hypothalamic activation by
afferent collaterals is dampened. Hypothalamic
influence on pituitary is reduced. As a result FSH,
LH, ACTH levels are lowered, while prolactin and
GH levels are raised

7. 3. CVS : Morphine causes vasodilatation due to:
(a) histamine release.
(b) depression of vasomotor centre.
(c) direct action decreasing tone of blood vessels.
4. GIT : Constipation is a prominent feature of
morphine action.
5. ANS : Morphine causes mild hyperglycaemia
due to central sympathetic stimulation. It has
weak anticholinesterase action.

8. ADVERSE EFFECTS :
1. Side effects - Sedation, mental clouding,
lethargy.
2. Idiosyncrasy and allergy - Allergy is uncommon
and anaphylactic reaction is rare. Urticaria, itch,
swelling of lips are the manifestations.
3. Apnoea - This may occur in the newborn when
morphine is given to the mother during labour.
4. Acute morphine poisoning - It is accidental,
suicidal or seen in drug abusers.
5. Tolerance and dependence - High degree of
tolerance can be developed to morphine and
related opioids if the drug is used repeatedly

9. PRECAUTIONS AND CONTRAINDICATIONS :
1. Infants and the elderly are more susceptible to the
respiratory depressant action of morphine.
2. It is dangerous in patients with respiratory
insufficiency, sudden deaths have occurred.
3. Bronchial asthma: Morphine can precipitate an
attack by its histamine releasing action.
4. Head injury: morphine is contraindicated in patients
with head injury.

10. USES :
1. As analgesic - Opioid analgesics are indicated in
severe pain of any type.
2. Preanaesthetic medication
3. Relief of anxiety and apprehension
4. Acute left ventricular failure (cardiac asthma)
5. Cough - Codeine or its substitutes are widely
used for suppressing dry, irritating cough
6. Diarrhoea - The constipating action of codeine
has been used to check diarrhoea and to
increase the consistency of stools in colostomy

11. OPIOID RECEPTORS :
1. μ ( Meu) receptor
2. κ ( Kappa ) receptor
3. δ ( Delta ) receptor
Opioid receptor activation reduces intracellular
cAMP formation and opens K+ channels (mainly
through μ and δ receptors) or suppresses voltage
gated Ca2+ channels (mainly κ receptor). These
actions result in neuronal hyperpolarization and
reduced availability of intracellular Ca2+ →
decreased neurotransmitter release by CNS and
myenteric neurones

12. OPIOID ANTAGONISTS :
1. Agonist-antagonists (κ analgesics)
Ex -Nalorphine, Pentazocine, Butorphanol
2. Partial/weak μ agonist + κ antagonist
Ex - Buprenorphine
3. Pure antagonists
Ex - Naloxone, Naltrexone, Nalmefene

13. Thanks