Model Answer
0 min readIntroduction
Morphine, an opioid analgesic derived from the opium poppy, remains a cornerstone in the management of moderate to severe pain. Its potent analgesic properties stem from its interaction with the opioid receptor system within the central nervous system. However, its use is associated with a range of adverse effects, including respiratory depression and addiction, necessitating a thorough understanding of its pharmacology and the principles of managing its toxicity. This answer will detail the mechanism of morphine’s analgesic effect, enumerate its adverse reactions, and outline the antidotal treatment for morphine poisoning.
Mechanism of Analgesic Effect of Morphine
Morphine exerts its analgesic effect primarily through its interaction with three main opioid receptor subtypes: mu (µ), kappa (κ), and delta (δ). The µ-opioid receptor is most crucial for analgesia.
- Receptor Binding: Morphine binds to µ-opioid receptors located in the brain (periaqueductal gray, thalamus, cortex) and spinal cord (dorsal horn).
- G-protein Coupled Receptor Activation: These receptors are G-protein coupled receptors. Upon activation, they inhibit adenylyl cyclase, reducing cAMP levels.
- Ion Channel Modulation: This leads to increased potassium conductance and decreased calcium conductance.
- Reduced Neuronal Excitability: The net effect is hyperpolarization of the neuron, reducing its excitability and inhibiting the transmission of pain signals.
- Descending Pain Pathway Activation: Morphine also activates descending inhibitory pathways originating in the brainstem, further suppressing pain transmission in the spinal cord.
- Supraspinal Effects: Morphine produces analgesia by altering the perception of pain, reducing anxiety and distress associated with pain.
Adverse Reactions of Morphine
Morphine’s adverse effects are numerous and can be categorized as follows:
| Category | Adverse Effects |
|---|---|
| Central Nervous System | Sedation, drowsiness, confusion, euphoria, dysphoria, hallucinations, respiratory depression (most serious), seizures (rare) |
| Gastrointestinal | Constipation (very common), nausea, vomiting, abdominal cramping |
| Cardiovascular | Bradycardia, hypotension, QT prolongation |
| Other | Pupillary constriction (miosis), urinary retention, itching (pruritus), sweating, allergic reactions, endocrine disturbances (decreased cortisol, testosterone) |
Antidotal Treatment in Morphine Poisoning
The primary antidote for morphine poisoning is naloxone, a competitive opioid receptor antagonist.
- Mechanism of Action: Naloxone has a higher affinity for opioid receptors than morphine, displacing morphine and reversing its effects.
- Administration: Naloxone is typically administered intravenously, intramuscularly, or intranasally.
- Dosage: Initial dose is typically 0.4-2 mg IV, repeated every 2-3 minutes as needed, titrated to effect (respiratory rate >12 breaths/min, improved mental status).
- Monitoring: Continuous monitoring of vital signs (respiratory rate, heart rate, blood pressure) is crucial.
- Supportive Care: Supportive care includes airway management (intubation and mechanical ventilation if necessary), oxygen therapy, and fluid resuscitation.
- Considerations: Naloxone’s duration of action is shorter than morphine’s, so repeated doses may be required until the effects of morphine wear off. Precipitation of withdrawal symptoms in opioid-dependent individuals is a potential complication.
Activated charcoal may be considered if the ingestion was recent (within 1 hour) and the patient is alert and able to protect their airway.
Conclusion
Morphine remains a valuable analgesic, but its use necessitates a comprehensive understanding of its mechanism of action, potential adverse effects, and the principles of managing its toxicity. Naloxone is the cornerstone of treatment for morphine overdose, but supportive care and careful monitoring are equally important. Ongoing research focuses on developing novel analgesics with reduced side effect profiles and lower addiction potential, aiming to improve pain management while minimizing the risks associated with opioid use.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.