Opioids are potent analgesics acting on the central and peripheral nervous systems. They include natural (morphine, codeine), semi-synthetic (oxycodone, heroin), and synthetic opioids (fentanyl, methadone). While widely used for pain control, opioid overdose is a major medical emergency due to respiratory depression and potential fatal outcomes.
Mechanism of Action
Opioids act mainly on mu (μ), kappa (κ), and delta (δ) receptors.
- μ-receptor activation → analgesia, euphoria, respiratory depression
- κ-receptor activation → sedation, dysphoria
- δ-receptor activation → analgesia and mood effects
Opioid Toxidrome (Classic Triad)
- CNS depression → drowsiness, coma
- Respiratory depression → slow, shallow breathing
- Miosis (pinpoint pupils)
This triad strongly suggests opioid overdose.
Clinical Features
CNS Effects
- Lethargy
- Slurred speech
- Coma in severe cases
Respiratory Effects
- Bradypnea (RR < 12/min)
- Shallow respiration
- Cyanosis due to hypoxia
Cardiovascular
- Bradycardia
- Hypotension
Gastrointestinal
- Constipation
- Nausea and vomiting
Severe Toxicity
- Apnea
- Noncardiogenic pulmonary edema
- Cardiac arrest
Diagnosis
- Clinical findings (classic triad)
- Response to naloxone
- Blood gases showing hypercapnia and hypoxia
- Urine drug screen for opioids
Management
1. Initial Stabilization
- Ensure airway patency
- Provide oxygen
- Assist ventilation if needed
2. Naloxone (Antidote)
Naloxone is a pure opioid antagonist.
- Initial dose: 0.04–0.4 mg IV/IM/IN
- Titrate up to restore breathing
- Repeat doses may be required for long-acting opioids (methadone)
Note: Naloxone can precipitate acute withdrawal in dependent individuals (agitation, vomiting, tachycardia).
3. Supportive Care
- Monitor respiratory rate and oxygen saturation
- Maintain IV access
- Treat hypotension with fluids
- Continuous observation for 4–6 hours after naloxone
4. Management of Complications
Pulmonary Edema
- Oxygen and positive pressure ventilation
Rhabdomyolysis (from prolonged immobilization)
- IV fluids and CK monitoring
Seizures (rare; mostly with tramadol or meperidine)
- Benzodiazepines
Chronic Opioid Toxicity
- Tolerance and dependence
- Withdrawal symptoms: lacrimation, yawning, diarrhea, sweating
- Risk of overdose due to variable drug purity (heroin)
Opioid Withdrawal (Not Life-Threatening)
- Anxiety and irritability
- Muscle cramps
- Gooseflesh (“cold turkey”)
- Diarrhea
Prevention & Harm Reduction
- Educate on overdose signs
- Naloxone kits for high-risk individuals
- Avoid mixing opioids with alcohol or sedatives
- Supervised opioid substitution therapy (methadone, buprenorphine)
Detailed Notes:
For PDF style full-color notes, open the complete study material below:
PATH: PHARMD/ PHARMD NOTES/ PHARMD FOURTH YEAR NOTES/ CLINICAL TOXICOLOGY/ OPIOIDS.