Excretion of lignocaine and its metabolite monoethylglycinexylidide in breast milk following its use in a dental procedure

The excretion of lignocaine in breast milk has been documented in a 34-year-old woman following the injection of 20 mg lignocaine for a dental alloy restoration in the right upper quadrant. Lignocaine and its primary metabolite monoethylglycinexylidide in milk and plasma were quantified by high-performance liquid chromatography. The concentration of lignocaine in milk ranged from 44-66 mug l-1 while that for monoethylglycinexylidide ranged from 35-41 mug l-1. The milk:plasma ratios for lignocaine and monoethylglycinexylidide were 1.1 and 1.8, respectively. The calculated daily infant doses for the parent drug and metabolite were both less than 0.01 mg kg-1 day-1. With the exception of very rare allergic reactions, these levels of infant exposure are extremely low and of no toxicological significance. Nursing mothers receiving lignocaine for standard dental procedures can be advised that continuation of breast feeding is safe.