Local anaesthetic effect of topical amethocaine gel in neonates: randomised controlled trial

To assess the efficacy of amethocaine as a topical local anaesthetic in neonates.

A randomised, double blind controlled trial compared 4% amethocaine gel (Ametop) with placebo in 60 healthy neonates (29 to 42 weeks of gestation) in the first week after birth. Either 1.5 g 4% w/w amethocaine (gel) or 1.5 g placebo gel were applied to the dorsum of one foot. No gel was applied to the other foot. Each foot was occluded and left for one hour. Local anaesthesia was then assessed by eliciting the cutaneous withdrawal reflex in response to stimulation with a series of graded nylon filaments (von Frey hairs). The reflex was first elicited from the control and then the treated foot. The difference in filament thickness and deforming weight required to elicit the reflex was recorded.

In infants treated with amethocaine, 17 of 31 (54. 8%) showed evidence of local anaesthetic action compared with five of 29 (17.2%) in the placebo group (p=0.003). The mean difference in deforming weight required to elicit the reflex was 18.8 g in the amethocaine group compared with 3.9 g in the placebo group (p=0.02). The apparent local anaesthetic action of the placebo can be explained by habituation to repeated stimulation.

It is concluded that topical amethocaine gel has a local anaesthetic action on neonatal skin which merits further investigation. An effective and safe surface local anaesthetic would be valuable for the relief of procedure related pain in neonates.