In children, the addition of epinephrine modifies the pharmacokinetics of ropivacaine injected caudally.
OBJECTIVE
To describe the modification of the ropivacaine (R) pharmacokinetics produced by the addition of epinephrine (E).


METHODS
After Institutional Review Board approval, 18 ASA I boys received a caudal block (1 mL x kg(-1)) with either plain 0.2% R (Group E-) or with 0.2% R containing E (5 microg x mL(-1); Group E+). Venous blood samples were taken at zero, 15, 30, 60, 90, 120, 180, 240, 420, 720, 1440 min after caudal injection. Total R concentration in plasma was determined by high pressure liquid chromatography. Maximal concentration (C(max)) and time to peak concentration (T(max)) were obtained from the data, terminal half-life (T(1/2z)), clearance (Cl) and volume of distribution (Vd) were estimated by a non-compartmental approach. Subsequently, in order to determine the absorption rate (Ka) and to reduce to number of blood samples, 25 other children, receiving plain R and another group of 25 receiving the E solution were studied using a population approach (NONMEM). A one compartment model with first order absorption was used. The effect of weight, age and E on Cl, Vd and Ka was estimated.


RESULTS
C(max) was significantly lower in Group E+ (0.93 mg x L(-1) +/- 0.29 vs 0.61 mg x L(-1) +/- 0.28, P = 0.05) and T(max) occurred later (124 min +/- 53 vs 47 min +/- 16, P = 0.003). Weight was a significant covariate for Cl and Vd while E significantly slowed R Ka [Group I Ka 0.025 min(-1) [coefficient of variation (CV) 21%] vs 0.078 min(-1) (CV 25%) in Group II].


CONCLUSIONS
The addition of E significantly modifies the pharmacokinetics of R injected caudally.
Van Obbergh
Luc J
LJ
Department of Anesthesiology, Université catholique de Louvain, Brussels, Belgium. vanobbergh@anes.ucl.ac.be
Roelants
Fabienne A
FA
Veyckemans
Francis
F
Verbeeck
Roger K
RK
D000367:Age Factors; D000577:Amides / Q000008:administration & dosage / Q000493:pharmacokinetics*; D000779:Anesthetics, Local / Q000493:pharmacokinetics*; D002675:Child, Preschool; D004347:Drug Interactions; D004837:Epinephrine / Q000494:pharmacology*; D006801:Humans; D007223:Infant; D000077212:Ropivacaine
D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine; D004837:Epinephrine