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Substance education guide

Meperidine / Pethidine (Demerol)

Synthetic phenylpiperidine opioid · Atypical analgesic · Normeperidine neurotoxicity

· How it works

Classification and primary mechanism

Meperidine is a full mu-opioid agonist with anticholinergic, weak serotonin-reuptake-inhibiting, and local-anesthetic activity. Its metabolite normeperidine lasts longer and can accumulate, lowering the seizure threshold and causing central neurotoxicity.

· Immediate effects

Recognize the effects

Signs of Use

  • Analgesia, sedation, dry mouth, and mild tachycardia
  • Confusion, agitation, hallucinations, or mood lability
  • Muscle twitching, tremor, hyperreflexia, or dilated pupils
  • Slow or absent breathing with toxic delirium
  • Generalized seizure or unresponsiveness

Short Term

  • Therapeutic exposure: analgesia, sedation, dry mouth, and normal or dilated pupils
  • Repeated or high dosing: confusion, agitation, myoclonus, tremor, and hallucinations
  • Severe toxicity: normeperidine seizures combined with opioid respiratory depression
  • Risk rises with kidney disease and repeated dosing
  • Serotonin toxicity is possible with serotonergic medicines

Long Term

  • Normeperidine encephalopathy and recurrent seizures
  • Physical dependence and opioid withdrawal
  • Falls, aspiration, and cognitive impairment
  • Greater toxicity with reduced renal clearance

· Long-term consequences

Mixed opioid and neurotoxic toxidrome

Call 911. Naloxone can restore breathing but does not treat normeperidine seizures; clear nearby hazards, do not restrain the person, and await hospital seizure management.

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