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Toxicology – Opioid (Opiate) Toxidrome
Sources
Opioid toxicity can result from a wide range of substances, including natural and synthetic narcotics such as morphine, heroin, codeine, oxycodone, hydrocodone, fentanyl, methadone, hydromorphone, buprenorphine, oxymorphone, meperidine, propoxyphene, opium, and kratom. These agents may be taken orally, inhaled, or injected. Many prescription formulations combine opioids with acetaminophen, and fentanyl is also available as a transdermal patch.
Typical Presentation
Patients often present with decreased level of consciousness and respiratory depression. A classic presentation includes somnolence, slow breathing, pinpoint pupils, and evidence of intravenous drug use such as track marks. Administration of naloxone can rapidly reverse symptoms, leading to abrupt awakening.
Clinical Features
Common findings include central nervous system depression, bradypnea, bradycardia, reduced bowel sounds, and miosis. Peripheral vasodilation may result in hypotension and hypothermia. Severe toxicity can lead to respiratory arrest and coma. Complications may include noncardiogenic pulmonary edema and, in certain cases such as methadone use, QT prolongation. Repeated dosing of meperidine may provoke seizures.
Mechanism of Action
Opioids exert their effects by binding to specific opioid receptors in the central nervous system and gastrointestinal tract, leading to decreased neuronal excitability and slowed physiological functions.
Management
Treatment is primarily supportive, with airway and breathing support as needed. Naloxone is the antidote and should be administered in small, titrated doses (0.4–2 mg in adults, 0.1 mg/kg in children) every 1–2 minutes until adequate ventilation is restored. Care should be taken to avoid precipitating acute withdrawal. For long-acting opioids, a continuous naloxone infusion (approximately two-thirds of the effective reversal dose per hour) may be required. Whole bowel irrigation may be considered in cases of ingestion of sustained-release formulations or transdermal patches.
Key Points
- Naloxone has a shorter duration of action than many opioids, so repeated dosing or infusion may be necessary.
- Prolonged unconsciousness can lead to complications such as rhabdomyolysis.
- Some opioids, such as propoxyphene, may cause cardiac conduction abnormalities and seizures.
- Many opioid combination products contain acetaminophen, increasing the risk of combined toxicity.
- Transdermal systems and “abuse-deterrent” formulations may still be misused through extraction methods.
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