Pethidine hydrochloride

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.