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A risk-benefit assessment of topical percutaneous local anaesthetics in children
1Department of Anaesthesia, Royal Hospital for Sick Children, Edinburgh, Scotland.
Insights
Eutectic lidocaine-prilocaine cream (EMLA) and tetracaine gel are effective topical anesthetics with good safety profiles for procedures like venipuncture. While EMLA has rare risks in infants, its benefits outweigh them, making it a preferred choice.
Area of Science:
- Anesthesiology
- Dermatology
- Pharmacology
Background:
- Eutectic lidocaine-prilocaine cream (EMLA) is a widely used topical anesthetic for procedures like venipuncture and venous cannulation.
- EMLA demonstrates high efficacy and an excellent tolerability profile, with adverse effects being rare.
Purpose of the Study:
- To review the efficacy, tolerability, and safety of various topical anesthetic preparations.
- To compare EMLA with newer agents like tetracaine gel and older formulations such as TAC paste.
Main Methods:
- Review of clinical practice and published literature on topical anesthetic agents.
- Analysis of risk-benefit profiles for different anesthetic preparations.
Main Results:
- EMLA is highly effective and well-tolerated, with risks primarily limited to oral ingestion or methaemoglobinaemia in neonates.
- Tetracaine gel offers faster onset and longer duration than EMLA with a good safety record.
- TAC paste is associated with higher toxicity and poorer tolerability compared to EMLA and tetracaine gel.
Conclusions:
- EMLA remains a favorable option for topical anesthesia due to its efficacy and safety.
- Tetracaine gel is a viable alternative with improved pharmacokinetic properties.
- Other agents like iontophoretic lidocaine and TAC paste have limitations in terms of administration complexity or safety.
Abstract:
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.