Prilocaine

Prilocaine is an amide-type local anesthetic used to produce local and regional anesthesia. It is commonly used by injection for infiltration and nerve blocks, and in combination with lidocaine in topical preparations such as the eutectic mixture of local anesthetics (EMLA) cream. Commercial formulations include injectable prilocaine, sometimes with epinephrine (for example, Citanest Forte), and topical/dental products such as Oraqix and EMLA.

Mechanism of action is through reversible blockade of voltage-gated sodium channels in nerve membranes, preventing initiation and propagation of nerve impulses and producing loss of sensation in the affected area.

Pharmacokinetics and interactions: Prilocaine is primarily metabolized in the liver by amidases to inactive metabolites, which are excreted in the urine. Absorption and systemic exposure depend on dose, site, and use of vasoconstrictors; adding epinephrine reduces systemic uptake and prolongs effect. Prilocaine has a relatively favorable profile regarding vasodilation compared with some other local anesthetics, but clinicians often use vasoconstrictors to extend duration and limit spread.

Safety and cautions: A distinctive risk of prilocaine is methemoglobinemia, due to its metabolite o-toluidine, which is dose- and age-dependent. The risk is higher with large doses and in young children; EMLA is contraindicated in infants under about 1 year. Signs of methemoglobinemia include cyanosis and fatigue and require prompt evaluation. Other adverse effects mirror those of other local anesthetics and can include CNS excitation or depression and, in severe cases, cardiovascular toxicity.

See also: EMLA cream, Oraqix, Citanest.