Pharmacology for Dentistry

(Ben Green) #1
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-
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