ANALGESIC

Analgesics are the drugs which relive pain without causing loss of consciousness. Analgesics can be classified as:

  1. Narcotic analgesics
  2. Non-narcotic analgesics (NSAID)/non-steroidal anti-inflammatory drugs

1. Narcotic analgesic or Opioid analgesics:

This consists of opium alkaloid and their derivatives. They act on CNS and are used as to relive moderate to severe pain. To produce analgesic effect and other pharmacological action opium alkaloids and their derivatives has to bind with opium receptors. Opioid receptors are of many types such as mu, kappa, delta, sigma, which are located within the CNS.

CLASSIFICATION

  1. Natural opium alkaloids
    1. Phenanthrene derivatives ex: morphine, thebaine, codeine
    1. Benzyl isoquinoline derivatives ex: papaverine, noscapine
  2. Semi synthetic derivatives of opium alkaloids ex: heroin, apomorphine, dihydromorphine
  3. Synthetic derivatives ex: pethidine, pentazocine, methadone, nalbuphine MORPHINE

Morphine is a natural opium alkaloids obtain from the unripe capsule of the poppy plant, papaver somniferum used as a powerful analgesic.

PHARMACOLOGICAL ACTIONS

  1. Analgesic action: morphine is a potent analgesic and relieves pain without loss of consciousness.
  2. Action of CNS: morphine produces euphoria in the presence of pain, but in the absence of pain, and in increased dose it produce sleep.
  3. Respiratory action: morphine produces depression of respiration by directly depress the respiratory centre in the brain
  4. Pupils: morphine produces constriction of the pupil and higher dosage it characterized by pin point pupil.
  5. Emetics action: in small dose morphine produce vomiting due to stimulation of CTZ (chemo receptor trigger zone) but in higher dose it depress the vomiting center and hence there is no vomiting in poisoning.
  6. Antitussive effect: morphine suppresses cough of depressing the cough center
  7. ADH secretion: morphine produce release of ADH this result in decrease of urine output.
  8. GIT effect: morphine decrease the mortality of the gout and produces constriction of intestinal smooth muscle and increase absorption of water and it all leads to constipation
  9. CVS effect: normal dose of morphine produce no effect on heart or circulation but hypotension may be produced at toxic dose.

PHARMACOKINETICS

Given orally, absorption of morphine is slow an incomplete and undergoes extensive first pass metabolism. Quick effect is produce on subcutaneous injection. It is metabolized in liver and excreted through urine and bile.

ADVERSE EFFECTS

Acute morphine poisoning: It cause due to accidental overdose and suicidal intention, characterized by respiratory depressant, pin point pupil, hypotension, hypothermia, cyanosis, coma and death.

Treatment

  • Positive pressure respiration
  • Maintenance of blood pressure
  • Gastric lavage with kmo4 to remove unabsorbed drug
  • Specific antidote, naloxone 0.4 to 0.8 mg i.v repeated every 10 to 15min
  • Tolerance and drug dependence
  • GIT effect: nausea, vomiting, constipation,
  • CNS: diasphoria, mental changes
  • Intolerance: skin rashes, tremors, delirium

USES

  1. As an analgesic for relief of severe pain
  1. Treatment diarrhoea
  2. As an Antitussive
CODEINE

It is a naturally opium alkaloids codeine depress the cough centre in a low dose. it is less potent than morphine as an analgesic . it produce less respiratory depression and less constipation and less chance of addiction

It is well absorbed when given orally compared to morphine constipation is the most common side effect.

USES: It is used as antitussive. OPOID ANTAGONIST

These are the drugs which antagonized the effect of morphine and other opioid analgesic. Ex: naloxane, naltrexone

NALOXONE

It is pure opioid antagonist. These group agents are used to antagonize the respiratory depressant sedative effect and other untoward effect and morphine like drugs.

USES

  • It is used as antagonist in opioid poisoning and drug of choice for morphine overdose
  • It is used to reverse neonatal asphyxia due to opioid used in labor

NALTREXONE

It is pure opoid antagonist which can be given orally it is twice as active as naloxone with three times its duration of action.

USES
  • It is a drug of choice for deaddiction in patient addicted to heroin like opioids