Toxicity of local application of a mixture of anesthetics: Lidocaine and prilocaine cream in an experimental model

Abstract

Objective: To determine genotoxicity, cytotoxicity and methemoglobinemia of a mixture of lidocaine (LD) and prilocaine (PL) (EMLA^®) in an experimental model. Study design: Newborn hairless rats were studied in a prospective random and masked design. Groups I–III received topically LD-PL mixtures at 5, 10 or 20% respectively, group IV: petrolatum (negative control); group V: 5-fluorouracil 5% (genotoxicity and cytotoxicity positive control); and group VI: aniline (methemoglobinemia positive control). Blood samples were collected every 24 h from 0–144 hours. Genotoxicity and cytotoxicity were assessed by the micronucleus assay. Changes in micronucleated erythrocytes and micronucleated polychromatic erythrocytes evaluated genotoxicity, and polychromatic erythrocytes in 1,000 total erythrocytes were used to determine cytotoxicity. Methemoglobin values were quantified by spectrophotometry. Results: The micronucleated erythrocytes number increased proportionally to the LD-PL mixture dose (p = 0.04), from 60% in group II until 90% in group III in relation to their basal value; however, no cytotoxicity effect was observed. Methemoglobin values increased in groups II, III, V and VI from the second day (p < 0.05). Conclusion: Topical administration of LD-PL mixture (10% and 20%) to neonatal rats show genotoxic effects and produces methemoglobinemia. Clinical implications of these findings require urgent further investigation before continuing to use LD-PL mixture routinely.