Prilocaine hydrochloride

How it works

It reversibly blocks voltage-gated sodium channels on nerve membranes, preventing depolarisation and propagation of the nerve impulse to produce local anaesthesia.

Prescribing in practice

• Excessive doses can cause methaemoglobinaemia (a metabolite oxidises haemoglobin), presenting as cyanosis unresponsive to oxygen, and it should be avoided in those with congenital or acquired methaemoglobinaemia and used cautiously in anaemia or significant cardiorespiratory disease.
• Inadvertent intravascular injection or overdose can cause systemic local anaesthetic toxicity, with CNS effects and cardiovascular depression, so use the lowest effective dose and aspirate before injecting.
• Use with caution in hepatic impairment, where metabolism is reduced, and in the elderly and debilitated.

Monitoring

Monitor for signs of systemic toxicity and for cyanosis suggesting methaemoglobinaemia during and after administration.

Counselling the patient

• Explain that numbness will develop in the area and wears off gradually, and to protect the numb area from injury.
• Report any drowsiness, dizziness, tingling around the mouth or unusual blue discolouration of the lips or skin.

Evidence & guidelines

Prilocaine has a recognised association with methaemoglobinaemia at higher doses, and management with intravenous methylene blue is well established for clinically significant cases.