A risk-benefit assessment of topical percutaneous local anaesthetics in children.

Since its introduction, eutectic lidocaine-prilocaine cream ('EMLA')1 has been found to be an effective topical anaesthetic agent, with a high degree of efficacy, particularly for venepuncture and venous cannulation, and an impressive tolerability profile. Reports of adverse effects are remarkable for their rarity. The only problems that are likely to be encountered are oral ingestion of the cream (which may lead to anaesthesia of the oropharynx and possible toxicity secondary to rapid absorption of local anaesthetic from oral mucous membranes) and methaemoglobinaemia following repeated applications in neonates and infants. Analysis of the risks and benefits associated with its use comes down heavily in favour of the preparation. More recently, a preparation of tetracaine (amethocaine) has been marketed as a gel. Its advantages are a faster onset, and longer duration, of action than 'EMLA'. Although less widely used, it too has an impressive tolerability record. Concerns over the potential for anaphylactic type reactions due to its ester structure have not been realised in clinical practice. Of the other available preparations, lidocaine (lignocaine), applied iontophoretically, is unlikely to become popular because of the complexity of administration. A paste made of tetracaine, epinephrine (adrenaline) and cocaine (TAC) appears to be a far more toxic preparation on theoretical grounds, and this has been borne out in clinical practice; it is not as well tolerated as 'EMLA' or tetracaine gel. Ethyl chloride, although not a local anaesthetic, can safely provide cutaneous analgesia in children in circumstances when it is impractical to wait for a local anaesthetic preparation to take effect.