Lidocaine and its metabolites in the newborn.

Concentrations of lidocaine and its metabolites were measured chromatographically in the blood and urine of mothers and babies after epidural administration of lidocaine to the mother for cesarean delivery. Delivery occurred a mean time of 29.83 plus or minus 8.64 minutes after a mean dose of 398.33 plus or minus 63.38 mg to the mother, at which time mean maternal venous plasma concentration was 1.70 plus or minus 0.77 mug/ml. Of the total molar quantity of lidocaine and metabolite recovered from the newborns' urine in the first 12 hours of life, 50.63 per cent appeared as unchanged lidocaine, while 49.37 per cent appeared as metabolites. In the second 12 hours of life, 23.37 per cent appeared as unchanged lidocaine, while 76.63 per cent appeared as metabolites. We conclude that the greater proportion of metabolite excretion in the second 12 hours is evidence that the new born is capable of metabolizing lidocaine.