Pharmacokinetics of lignocaine in children after infiltration for cleft palate surgery

Human variability in CYP3A4 metabolism and CYP3A4-related uncertainty factors for risk assessment

CYP3A4 constitutes the major liver cytochrome P450 isoenzyme and is responsible for the oxidation of more than 50% of all known drugs. Human variability in kinetics for this pathway has been quantified using a database of 15 compounds metabolised extensively (>60%) by this CYP isoform in order to develop CYP3A4-related uncertainty factors for the risk assessment of environmental contaminants handled via this route. Data were analysed from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration-time curve (AUC)] and acute exposure (Cmax). Interindividual variability in kinetics was greater for the oral route (46%, 12 compounds) than for the intravenous route (32%, 14 compounds). The physiological and molecular basis for the difference between these two routes of exposure is discussed. In relation to the uncertainty factors used for risk assessment, the default kinetic factor of 3.16 would be adequate for adults, whereas a CYP3A4-related factor of 12 would be required to cover up to 99% of neonates, which have lower CYP3A4 activity.

Serum lidocaine concentrations after subcutaneous administration in patients undergoing cardiac catheterization in a pediatric institution

OBJECTIVE

We wished to determine serum lidocaine concentrations after subcutaneous injection during cardiac catheterization.

METHOD

Serum lidocaine concentrations were measured in 50 patients during catheterization.

RESULTS

Serum concentration was linearly related to dose per kilogram of body weight. Lidocaine concentrations were therapeutic in 38% of patients.

CONCLUSION

Lidocaine dose must be considered when the drug is used for local anesthesia in children.

Plasma concentrations of lignocaine after thoracic paravertebral blockade in infants and children

Plasma concentrations of lignocaine were determined in six ASA 1 children treated with thoracic paravertebral blockade. Peak concentrations ranged between 1.7 and 3.0 micrograms.ml-1 after a bolus injection of lignocaine 0.5 ml.kg-1 (lignocaine 10 mg.ml-1 with adrenaline 5 micrograms.ml-1) and peak plasma concentrations were reached 15-30 min after injection. Two hours after the initial bolus a continuous infusion of the same lignocaine solution was started (0.25 ml.kg-1.h-1). Steady state levels of lignocaine were reached 8-10 h after the start of the infusion and ranged from 2.1-3.2 micrograms.ml-1. This regimen for paravertebral block in children resulted in moderate plasma concentrations of lignocaine, well below those which might result in side effects or systemic toxicity.