A topical formulation of the
ester-type
local anesthetic amethocaine (
tetracaine) [
Ametop ] is currently available for reducing
pain from cutaneous procedures such as venipuncture. The
Ametop mark preparation contains 40 mg of
amethocaine base (4% w/w) and produces
anesthesia within 30-45 minutes of application; duration of action ranges from 4 to 6 hours. Clinical studies have demonstrated the superiority of the 4%
amethocaine preparation over placebo in pediatric populations for indications such as intravenous cannulation, vaccination, and venipuncture.
Amethocaine has been shown to produce
anesthesia comparable to that of 5%
lidocaine-prilocaine for procedures such as venipuncture and accessing centrally placed devices; in
general, anesthesia was achieved more rapidly with
amethocaine than
lidocaine-prilocaine. In the neonatal population
amethocaine was found to be ineffective at reducing the
pain of heel prick and peripherally inserted central
catheters. Depending on the type of procedure,
amethocaine application times between 30 and 60 minutes have produced clinically acceptable
anesthesia; application times <30 minutes have not been associated with reliable
anesthesia. The 4%
amethocaine preparation is well tolerated; the most commonly reported local skin reaction is transient local
erythema while local
edema and
itching have been reported more rarely. There have been no accounts of systemic toxicity with topical use of the preparation. Several cases of sensitization have been described in adults upon repeated exposure to topical
amethocaine. In summary, the novel preparation of 4%
amethocaine gel has been shown to be clinically effective for managing
pain associated with minor cutaneous procedures while maintaining a good tolerability profile.
Amethocaine has also demonstrated similar efficacy to
lidocaine-prilocaine when appropriate application times are used; the more rapid onset of action and extended duration of action of
amethocaine may make it more useful than
lidocaine-prilocaine in busy clinical settings.