Pharmacology for Dentistry

78 Section 2/ Drugs Acting on CNS

• Stomach lavage with potassium per-
  manganate.


• Enhancing excretion of unabsorbed
  morphine from the intestine.


• Acidify the urine to enhance the renal
  excretion of morphine.

Contraindications

1. Head injury, because morphine can
   cause increase in intracranial tension,
   cause marked respiratory depression
   and certain physiological signs e.g.
   miosis and vomiting can interfere
   with the assessment of clinical
   progress.


2. Myxoedema patients are more sensi-
   tive to morphine.


3. Bronchial asthma: Morphine releases
   histamine which can trigger
   bronchoconstriction.


4. In liver damage chance of cumulative
   toxicity is more.


5. In elderly patients, chances of urinary
   retention are high.


6. In hypotensive states, more fall in
   blood pressure occurs due to morphine.

Therapeutic Uses

1. Analgesia: Morphine is used in the fol-
   lowing painful conditions:
   
   
   • In the treatment of any severe, con-
     stant pain.
   
   
   • Visceral pain e.g. myocardial infrac-
     tion, pleurisy, vascular occlusion,
     renal and biliary colic.
   
   
   • Traumatic pain e.g. long bone frac-
     tures and burns.
   
   
   • Pain of terminal illness e.g. in can-
     cer patients.
     
     
     • Postoperative pain.
     
     
     • Obstetrical analgesia.
     
     
     
     
   
   
   
   


2. In the suppression of cough and dysp-
   nea (due to left ventricular failure and
   pulmonary edema).


3. For sedation.


4. In the treatment of diarrhoea.


5. As preanaesthetic medication.


6. In the treatment of acute left ventricu-
   lar failure.


7. Use of opioids in dentistry is very limited.
   CODEINE
   It is a methyl ester of morphine and less
   potent analgesic than morphine. It is widely
   used as antitussive agent. Pholcodeine is
   also used as antitussive agent and causes
   less constipation (Details are given in chap-
   ter ‘Drugs acting on respiratory system’).

SYNTHETIC COMPOUNDS

PETHIDINE

Pethidine is predominantly a μ agonist and

it exerts its action on the CNS and the neural

elements in the bowel. In equianalgesic doses,

pethidine produces as much sedation, respira-

tory depression and euphoria as does morphine.

A few patients may experience dysphoria.

The analgesic effects of pethidine are

detectable about 15 minutes after oral ad-

ministration, reach a peak in about two

hours and subside gradually over several

hours. Pethidine is absorbed by all routes of

administration, but the rate of absorption is

erratic after IM injection. Pethidine crosses

the placental barrier.

Pethidine is metabolized chiefly in the

liver, to mainly meperidinic acid and minor

metabolite norpethidine, which are conju-