Opioid Pharmacology Quiz

Study Notes

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 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)

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

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: 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

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