Opioid Pharmacology Quiz

Analgesics

• Analgesics are drugs that relieve pain by acting on the central nervous system (CNS) or peripheral pain mechanisms without significantly altering consciousness.
• Types of analgesics include:
  • Opiates and opioids
  • NSAIDs
  • Analgesic antipyretics
  • Drugs for neurological pain

Opiates and Opioids

• Opiates are naturally occurring compounds derived from the opium poppy plant.
• Opiates contain:
  • Phenanthrene ring: Causes more CNS effects, addiction, and spasm (e.g., morphine, codeine, thebaine)
  • Benzylisoquinoline ring: Causes less CNS effects and does not cause addiction (e.g., papaverine, noscapine, narcine)
• Opioids are a broader class of agents.
  • Some opioids have similar effects to opium (e.g., heroin, hydromorphone)
  • Other opioids bind to opioid receptors (e.g., meperidine, methadone, tramadol)
    • Some act as agonists
    • Some act as mixed agonist-antagonists (e.g., nalorophine, nalbuphine, pentazocin, butorphanol, bupermorphine)
    • Some act as antagonists (e.g., naloxone, naltrexone)

Morphine

• Main medical uses: Management of acute and chronic pain, pulmonary edema

• It is abused for its euphoric and pain-relieving effects, causing physical and psychological dependence

• Routes of administration: Primarily oral, intravenous (IV), intramuscular (IM), subcutaneous (SC), epidural

• After oral intake, only 25% of the dose is bioavailable

• Receptors: Mu, delta, kappa

• Mechanisms of pain relief:

  • Interference with neurotransmitter (substance P) in the spinal cord
  • Inhibition of neurotransmission from higher brain centers
  • Decreases noradrenaline release (enhancing emotional sensation of pain) in the brain
  • Peripherally decreases pain sensation in inflamed tissue

• Morphine does not relieve itching, but it increases itching due to histamine release

• Pharmacological effects include:

  • Analgesia (physical and emotional pain)
  • Euphoria
  • Miosis (pupillary constriction)
  • Vagal stimulation
  • Nausea and vomiting
  • Respiratory depression
  • Cough suppression
  • Increased intracranial pressure

• Cardiovascular (CVS) effects include bradycardia (slow heart rate) and hypotension (low blood pressure)

• Gastrointestinal (GIT) effects include constipation and gall bladder spasm

• Genitourinary effects include urgency or difficulty passing urine, and prolonged labour

• Respiratory effects include bronchospasm, cough suppression

• Skin effects include itching

Acute Overdose (Intoxication)

• Symptoms:
  • Respiratory depression, bronchospasm, non-cardiogenic pulmonary edema (acute lung injury)
  • CNS depression (preceded by anxiety, agitation, euphoria or dysphoria)
  • Seizures (due to hypoxia)
  • Pinpoint pupils
  • Hypotension and bradycardia
  • Hypothermia
  • Pruritis (itching)
  • Constipation
• Causes of death: Respiratory depression, pulmonary edema, dysrhythmia, irreversible brain damage due to prolonged hypoxia -Fatal dose: 100mg or 2-3 grams of opium

Diagnosis and Management

• Diagnosis: Pontine hemorrhage, other toxin exposures
• Investigations: ABG, pulse oximetry, ECG, urea, electrolytes, creatinine, glucose, CXR, AXR, urine screening
• Management:
  • Emergency measures (ABCs)
  • Antidote: Naloxone (Narcan)
  • Elimination: Gastrointestinal lavage, activated charcoal, whole bowel irrigation
  • Supportive care: IV fluids, anti-arrhythmic drugs, anti-convulsants, management of pulmonary edema (especially important with overdose), and management of coma

Withdrawal

• Symptoms: Anxiety, agitation, hypertension, yawning, lacrimation, running nose, dilated pupils, tremors, piloerection, vomiting, diarrhea, muscle aches
• Death may be due to dehydration and collapse
• Management:
  • Admission and good diet
  • Detoxification (e.g., methadone, clonidine) providing supportive care (pain, vomiting, diarrhea, adequate rehydration)
  • Psychotherapy, rehabilitation, and follow-up

Post Mortem Findings

• Asphyxial death
• Smell of opium
• Injection sites
• Morphine detected in body fluids (urine)