Preliminary study to assay plasma amethocaine concentrations after topical application of a new local anaesthetic cream containing amethocaine.

Plasma concentrations of amethocaine were measured after topical application of amethocaine cream 2 g (5% w/w) to the dorsum of the right hand of 10 adult volunteers. The cream was applied for 240 min and plasma was assayed for amethocaine and its metabolite p-n-butylaminobenzoic acid at 0, 30, 60, 90, 120 and 240 min in all 10 volunteers, and at 360 min in seven volunteers, by high pressure liquid chromatography. No amethocaine was detected in the plasma of seven volunteers. Plasma concentrations of amethocaine up to 0.20 mg litre-1 were observed in three volunteers. No significant side effects were seen and pain scores on insertion of a 16-gauge cannula were 0 in all subjects. We conclude that the absence of clinical toxicity in the 10 healthy volunteers was a reflection of slow absorption and tissue hydrolysis of amethocaine after topical dermal application.