Pharmacology for Dentistry

Narcotic Analgesics (Opioids) 77

CO 2 causes an increase in cerebrospinal fluid
pressure.

Action on cough centre: Morphine sup-
presses cough reflexes, but cough suppres-
sion by opioids may allow accumulation of
respiratory secretions and may produce air-
way obstruction.

Chemoreceptor trigger zone (CTZ):
Morphine stimulates CTZ and produces
nausea and vomiting. These effects are more
marked in upright position due to vestibu-
lar involvement.

Vagal centre: Morphine stimulates the
vagal centre and produces bradycardia.

Effect on GIT: It increases the tone of
smooth muscle as well as sphincters but at
the same time it decreases the propulsive
movements and gastrointestinal secretions
are diminished, the overall action is consti-
pation.

Other smooth muscle: Morphine causes
bronchoconstriction which is due to hista-
mine release and may be dangerous in pa-
tients suffering from bronchial asthma.

Morphine also cause flushing and itch-
ing of skin due to histamine release.

Urinary system: Morphine causes
spasm of detrusor as well as sphincters of
urinary bladder and causes distension, ur-
gency and difficulty in micturition.

Endocrine system: Morphine and other
opioid analgesics stimulate the release of
vasopressin and prolactin and inhibit the
release of luteinizing hormone, ACTH and
follicle stimulating hormone.

Metabolism: Morphine decreases the
metabolic rate which can lead to decrease

in body temperature. It also depresses tem-

perature regulating centre.

Pharmacokinetics

Morphine orally is less effective and

absorption is very slow. It has variable and

high first pass metabolism when given by

subcutaneous route, its analgesic effect starts

within 10 minutes which persists for 4 to 5

hours and by IV route, it produces immedi-

ate action. In plasma, it binds to plasma pro-

teins (approx. 30%). In liver it is metabolized

by conjugation to glucuronic acid to form

active and inactive products, which are ex-

creted in urine. It is also excreted though bile

and in the faeces.

Adverse Reactions

CNS side effects include confusion, anxi-

ety, lethargy, nausea and vomiting. GIT re-

lated effect is constipation. Other side effects

are urinary retention, dry mouth, miosis,

dysphoria, hypotension, skin rash, itching

and urticaria. Tolerance, drug dependence

and drug abuse are the main drawbacks of

morphine.

Acute Overdose/Toxicity (Morphine

Poisoning)

It is characterised by respiratory depres-

sion, miosis, cyanosis, reduced body tem-

perature, urinary retention, hypotension,

pulmonary edema and coma.

The acute poisoning can be treated by:

• Maintenance of airway and oxygen in-
  halation. Maintenance of BP.


• Specific antagonists: Naloxone 0.4-0.8
  mg IV; alternatively nalorphine (3-5 mg
  IV) can be given.