Strong opioid (synthetic phenylpiperidine) Pregnancy: SPC 4.6: inadequate evidence of safety in human pregnancy, but the drug has been in wide use for many years without apparent ill consequence and animal studies have not shown any hazard - assess the risk/benefit ratio. Regular use during pregnancy may cause drug dependence in the foetus leading to neonatal withdrawal symptoms; administration during labour may depress respiration in the neonate and an antidote for the child should be readily available. Breast-feeding: administration to nursing women is not recommended (may be secreted in breast milk and may cause respiratory depression in the infant).

Pethidine hydrochloride

Pethidine hydrochloride is a synthetic opioid analgesic used for moderate to severe acute pain, including in obstetrics.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Moderate or severe pain: 25-100 mg by intramuscular or subcutaneous injection, or 25-50 mg by slow intravenous injection

Route: Intramuscular, intravenous or subcutaneous injection

Frequency: Normal single dose, usually not to be repeated more often than 4-hourly

Max: Maximum of 400 mg in 24 hours (stated in SPC 4.2 under obstetric analgesia)

Other regimens stated in SPC 4.2: obstetric analgesia 50-100 mg by intramuscular or subcutaneous injection, repeated 1-3 hours later, maximum 400 mg in 24 hours; premedication 50-100 mg by intramuscular injection one hour prior to the operation; enhancement of analgesia 10-25 mg by slow intravenous injection as required. Elderly or debilitated patients: initial doses should not exceed 25 mg, as this group may be especially sensitive to the central depressant effect of the drug. SPC 4.4: use with caution or in reduced doses in myasthenia gravis; use with caution and in reduced doses in neonates, premature infants, elderly or debilitated patients and those with impaired hepatic or renal function; caution in shock, hypothyroidism, adrenocortical insufficiency, history of convulsive disorders, prostatic hypertrophy, biliary tract disorders, existing hypotension; avoid in severe inflammatory bowel disease. Prior to starting opioid treatment a strategy for ending treatment should be agreed with the patient to minimise the risk of addiction and drug withdrawal syndrome. Pethidine is controlled under the Misuse of Drugs Act 1971 (Schedule 2). NOTE: SPC section 4.5 was not captured in this source bundle - the interaction entries in this draft are drawn from sections 4.3 and 4.4; a full 4.5 review is still required.

Paediatric dose

Route: Intramuscular injection

Frequency: Not stated for the paediatric dose in SPC 4.2; the premedication dose is given one hour prior to the operation

SPC 4.2 states ranges, not single per-kg values: moderate or severe pain 0.5-2 mg per kg of body weight by intramuscular injection; premedication 1-2 mg per kg of body weight by intramuscular injection one hour prior to the operation. SPC 4.4 states pethidine should only be given with caution and in reduced doses to neonates and premature infants, and that pethidine has a slower elimination rate and larger inter-subject variability in neonates and young infants (up to 12 months), which may lead to dose-related reactions such as respiratory depression - in this group potential benefits must be weighed against relative risk. Verify against a children's formulary before use.

Dose adjustments

Renal

Contraindicated in severe renal impairment (SPC 4.3). SPC 4.4: give only with caution and in reduced doses to patients with impaired renal function - renal impairment may result in accumulation of the potentially toxic metabolite norpethidine, particularly with repeat dosing. No numeric dose reduction is specified in the SPC.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Severe respiratory depression, severe obstructive airways disease or acute asthma
Severe renal impairment or severe hepatic impairment
Acute alcoholism, delirium tremens, raised intracranial pressure, or convulsive states such as status epilepticus (avoid)
Patients receiving monoamine oxidase inhibitors (including moclobemide, selegiline and rasagiline), or within two weeks of their withdrawal
Patients receiving ritonavir
Supraventricular tachycardia (avoid)
Phaeochromocytoma - use may result in hypertensive crisis
Diabetic acidosis where there is danger of coma (avoid)
Comatose patients, patients at risk of paralytic ileus, and patients with head injuries

Side effects

Respiratory depression (frequency unknown)
Drowsiness, dizziness, tremor, convulsions, headache, fainting, CNS excitation (frequency unknown)
Nausea, vomiting, dry mouth, constipation (frequency unknown)
Orthostatic hypotension, flushing, hypotension, hypertension, vasodilation (frequency unknown)
Tachycardia, bradycardia, palpitations (frequency unknown)
Drug dependence, confusion, altered mood, mild euphoria, hallucinations, dysphoria; drug withdrawal syndrome (frequency unknown)

Interactions

Monoamine oxidase inhibitors, including moclobemide and the monoamine B inhibitors selegiline and rasagiline - contraindicated, including within two weeks of withdrawal (SPC 4.3)
Ritonavir - contraindicated (SPC 4.3)
Sedative medicines such as benzodiazepines or related drugs - concomitant use may result in sedation, respiratory depression, coma and death; reserve for patients with no alternative treatment options, use the lowest effective dose for the shortest duration and monitor closely (SPC 4.4)

Clinical monograph

How it works

It is an agonist at mu-opioid receptors, producing analgesia and sedation; its metabolite norpethidine is a central nervous system stimulant that can accumulate.

Prescribing in practice

Avoid in patients taking or recently taking monoamine oxidase inhibitors, as the combination can cause severe and potentially fatal reactions including hyperpyrexia and excitatory states.
Accumulation of the metabolite norpethidine, especially in renal impairment or with repeated dosing, can cause tremor, agitation and convulsions, so prolonged or high-dose use is discouraged.
Like all strong opioids it causes respiratory depression, sedation and dependence, and the dose should be reduced in the frail or those with hepatic impairment.

Monitoring

Monitor respiratory rate, sedation level and pain response, and watch for neuroexcitatory features such as tremor or twitching with repeated dosing.

Counselling the patient

Warn the patient about drowsiness, dizziness and the risk of constipation and nausea.
Advise avoiding alcohol and not driving while affected.
Ensure the patient or carers know naloxone reverses opioid overdose and to seek help if breathing slows.

Evidence & guidelines

Pethidine is a long-established opioid analgesic; UK practice increasingly favours alternative opioids owing to norpethidine toxicity, consistent with its SPC and prescribing references.

Reference: FPM; UK guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways