Opioid Poisoning — Comprehensive Overview

1. Definition & Epidemiology

• In 2020, opioids were involved in 75% of all drug overdose deaths in the United States; 82.3% of opioid-involved deaths involved synthetic opioids (primarily fentanyl).
• Three epidemic "waves" have been described: (1) prescription opioids from the 1990s; (2) heroin from 2010; (3) synthetic opioids (fentanyl and analogues) from 2013 onward.
• Fentanyl is 50–100× more potent than morphine and 10× more potent than heroin.
• Street heroin purity in the U.S. has risen from ~4% to 45–75%, increasing the risk of unintentional overdose.

2. Receptor Pharmacology & Pathophysiology

• Respiratory depression: Direct narcotic depression of brainstem respiratory centers (medullary respiratory nuclei), causing shallow, slow respirations (2–8/min), periodic breathing, or complete apnea. This is the primary mechanism of death.
• CNS depression: Stupor, coma, unresponsiveness to stimulation.
• Miosis (pinpoint pupils): Mediated by the Edinger-Westphal nucleus; in late severe anoxia, pupils paradoxically dilate and become non-reactive.
• Cardiovascular depression: Bradycardia, hypotension (only dramatic with severe anoxia); cardiac arrhythmias may be related to anoxia or adulterants (e.g., quinine in heroin).
• Pulmonary edema: A frequent complication, particularly with heroin overdose (pathogenesis not fully understood).
• Hypothermia: Opiates suppress thermoregulation; however, by the time patients reach hospital, aspiration pneumonia may have caused normal or elevated temperature.
• Fentanyl-specific: Can produce respiratory muscle rigidity and laryngospasm ("wooden chest" syndrome), complicating bag-mask ventilation.

3. Clinical Presentation

The Classic Opioid Toxidrome (Triad)

Additional Signs

• Skin: Cold, clammy, cyanosis
• Temperature: Hypothermia
• Heart rate: Bradycardia; blood pressure decreased (dramatically only with severe anoxia)
• Neurological: Slurred speech, impaired attention, flaccid muscle tone
• GI: Nausea, vomiting, constipation (in milder intoxication)
• Pulmonary: Froth at mouth, X-ray evidence of pulmonary edema, aspiration pneumonia
• Late/severe: Pupils become large and non-reactive (from hypoxia, not the opioid itself); cardiovascular collapse

Mild Intoxication Signs

DSM-5 Criteria for Opioid Intoxication

1. Behavioral/psychological changes (initial euphoria → apathy, dysphoria, psychomotor agitation or retardation, impaired judgment)
2. Pupillary constriction
3. Drowsiness or coma
4. Slurred speech
5. Impairment in attention or memory

4. Populations at Increased Risk

• Children: Increased susceptibility; small doses may be toxic
• Adults with: myxedema, Addison disease, chronic liver disease, pneumonia
• Persons who have lost tolerance after a period of abstinence (formerly well-tolerated dose may be fatal on re-use)
• Polydrug users (opioids + benzodiazepines — major fatal combination)
• Users of illicit opioids with variable or unknown purity

5. Specific Drug Considerations

6. Diagnosis

• Recognise the opioid toxidrome: coma + pinpoint pupils + respiratory depression
• Toxicology screen (blood/urine): can confirm but delays management; standard screens may miss fentanyl analogues and novel synthetics
• Response to naloxone is both diagnostic and therapeutic (failure to respond should prompt consideration of other diagnoses)
• Consider co-ingestions: benzodiazepines (most common deadly combination), alcohol, other CNS depressants
• ECG: arrhythmias, QTc prolongation (especially methadone)

7. Management

Emergency Algorithm

Step-by-Step Management (Harrison's Table 467-2)

1. Establish and protect the airway — intubation and mechanical ventilation may be necessary
2. Assist ventilation — bag-mask ventilation; note that fentanyl may cause wooden chest syndrome requiring succinylcholine for intubation
3. Activated charcoal — for recent large oral ingestions
4. Naloxone (antidote — see below)
5. Monitor vital signs, oxygen saturation, respiratory rate, GCS
6. IV access, fluids — support blood pressure
7. Gastric lavage — may be useful for oral ingestion (even hours later, because opioid-induced ileus delays gastric emptying)
8. Treat co-ingestions — flumazenil 0.2 mg/min for benzodiazepines (caution: may precipitate seizures, ↑ICP)

Naloxone (Key Antidote)

Nalmefene (Newer Alternative)

• Higher potency, plasma half-life ~11 hours (vs. 60–90 min for naloxone)
• Recently approved for overdose treatment
• No clear advantage in emergency practice over naloxone per current evidence

8. Complications

9. Opioid Withdrawal

Detoxification Options

• Methadone: Administer 10 mg orally for objective withdrawal signs every 2–4 h for 24 h → this total is the "stabilization dose" (not to exceed 40 mg); then reduce by 5 mg/day
• Buprenorphine: Initiate after objective withdrawal signs appear (COWS score); taper over days
• α2-Adrenergic agonists (clonidine): 0.1–0.3 mg PO q1h (up to 4 doses); reduces autonomic withdrawal symptoms off-label

10. Longer-Term Treatment (Opioid Use Disorder)

11. Prevention

• Take-home naloxone: Patients discharged on >50 morphine milligram equivalents/day should receive naloxone prescription; friends and family trained in administration
• Intranasal naloxone kits (2 mg) are accessible for laypersons
• Warning patients about loss of tolerance after any period of abstinence
• Prescription drug monitoring programs
• Harm reduction: fentanyl test strips, supervised consumption

Recent Evidence Note