AIM To explore the time of onset and duration of action of topical amethocaine gel in the newborn infant.
DESIGN A randomised double blind placebo controlled trial.
SUBJECTS Thirty six infants were studied after 30 minutes application and 36 after 60 minutes application. A total of 56 infants (gestation 27–42 weeks, weight 0.79–4.1 kg) were studied in the first two weeks after delivery.
METHOD 1.5 g amethocaine or placebo was applied to the dorsum of either foot, occluded, and then left for 30 or 60 minutes. Local anaesthesia was assessed by observing the cutaneous withdrawal response to graded nylon filaments (von Frey hairs). If there was a difference between feet in filament thickness required to elicit a response, the infant was studied in an identical manner at hourly intervals until the difference had disappeared.
RESULTS Evidence of local anaesthetic action of amethocaine was seen in 23 of 36 (64%) infants after 30 minutes and 26 of 36 (72%) infants after 60 minutes application (no significant difference). Evidence of local anaesthetic action was independent of gestation and order of testing. Amethocaine responders showed a significantly deeper anaesthetic action than placebo responders. The median duration of action was 1.5 hours (range 0.5–3.5) after 30 minutes and three hours (range 1–5) after 60 minutes (p < 0.001).
CONCLUSION Topical amethocaine gel has a local anaesthetic action after 30 minutes application, but application for 60 minutes results in longer duration of action.
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