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Pharmacology · Opioids and antagonists

Pethidine !

A short-acting synthetic opioid. Its metabolite norpethidine builds up and causes tremor and seizures; with MAOIs it is dangerous.

Updated 2026-11-01

Also called: meperidine

The figure shows morphine in the μ receptor; pethidine, a phenylpiperidine, occupies the same site. There is no structure of pethidine in the receptor.

Target in 3D: μ-opioid receptor. PDB structure 8EF6 (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Pethidine is a synthetic μ agonist of the phenylpiperidine family. It relieves pain like other μ agonists and also has local anaesthetic properties. In the liver it is N-demethylated to norpethidine, a metabolite with a much longer half-life that stimulates the nervous system; with repeated doses or kidney disease it builds up and causes excitation, tremor, myoclonus and seizures.

  1. Activates the μ receptor in the pain pathway
  2. Short-lived pain relief
  3. The liver turns it into norpethidine, with a long half-life
  4. Built-up norpethidine excites the nervous system: seizures

Pharmacokinetics

Metabolism
Liver: N-demethylation to norpethidine and hydrolysis; in cirrhosis its bioavailability rises and its half-life lengthens.
Elimination
Kidney; norpethidine accumulates in renal failure.
Half-life
About 3 hours for pethidine and about 15 to 20 hours for norpethidine.

Indications

  • Acute pain needing an opioid, for a limited time
  • Obstetric analgesia and as a supplement to anaesthesia
  • Post-anaesthetic shivering

Adverse effects

Common

  • Lightheadedness, dizziness and sedation
  • Nausea and vomiting
  • Sweating

Contraindications

  • Significant respiratory depression
  • Acute or severe bronchial asthma without monitoring or resuscitation equipment
  • Known or suspected gastrointestinal obstruction, including paralytic ileus
  • Hypersensitivity to the drug
  • Current use of monoamine oxidase inhibitors or use within the last 14 days

Key interactions

Monoamine oxidase inhibitors
Contraindicated: severe reactions with excitation, hyperthermia, rigidity and serotonin syndrome, or profound depression.
SSRIs, SNRIs and other serotonergic drugs
Risk of serotonin syndrome.
Benzodiazepines, alcohol and other central nervous system depressants
Add up to profound sedation, respiratory depression, coma and death.

What is monitored

  • Respiratory rate and sedation
  • Tremor, myoclonus or agitation
  • Kidney function
  • Total duration of treatment

Administration and safety

  • Prolonged use raises the risk of norpethidine toxicity; it is not considered an opioid for chronic pain.
  • In older adults and in kidney disease it is used with great caution because norpethidine accumulates.
  • Intravenous doses are given slowly.
  • Controlled medicine: the order is verified, every dose recorded and leftovers kept secure.

Nursing care

  • Before each dose: respiratory rate, oxygen saturation and sedation level; hold the dose and report excessive sedation or slow breathing.
  • Keep naloxone at hand and teach the family to recognise an overdose.
  • Watch for tremor, muscle jerks, agitation or seizures, above all after several doses.
  • Check for use of MAOIs and serotonergic antidepressants.

Pregnancy and breastfeeding

Prolonged use in pregnancy can cause neonatal opioid withdrawal syndrome, which is expected and treatable; the newborn is watched after birth.

Test yourself

Think of the answer, then tap the question to see it.

Why is pethidine not used for chronic pain or in renal failure?

Because its metabolite norpethidine, long-lived and renally cleared, builds up and causes tremor, myoclonus and seizures.

What serious interaction does pethidine have with MAOIs?

It can cause serotonin syndrome with excitation, hyperthermia and rigidity, or profound depression; the combination is contraindicated.

Which specific anaesthetic use is pethidine remembered for?

Treating post-anaesthetic shivering.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Meperidine: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); MEPERIDINE HYDROCHLORIDE injection (DailyMed (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 23 (McGraw Hill, 2023); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.