Pharmacokinetics of remifentanil in anesthetized pediatric patients undergoing elective surgery or diagnostic procedures

Remifentanil hydrochloride is an ultra-short-acting opioid that undergoes r apid metabolism by tissue and plasma esterases. We aimed to characterize th e pharmacokinetics and determine the hemodynamic profile of remifentanil af ter a single-bolus dose in children aged 0 to 18 yr. Forty-two children und ergoing elective surgical procedures received remifentanil 5 mug/kg infused over 1 min. Patients were divided into age groups as follows: young infant s (less than or equal to2 mo), older infants (>2 mo to <2 yr), young childr en (2 to <7 yr), older children (7 to < 13 yr), adolescents (13 to < 16 yr) , and young adults (16 to < 18 yr). Arterial blood samples were collected a nd analyzed by mass spectroscopy to determine remifentanil pharmacokinetic profiles. Hemodynamic measurements for remifentanil's effect were made afte r the infusion. Methods of statistical analysis included analysis of varian ce and linear regression, with significance at P less than or equal to 0.05 . Complete remifentanil pharmacokinetic data were obtained from 34 patients . The volume of distribution was largest in the infants <2 mo (mean, 452 mL /kg) and decreased to means of 223 to 308 mL/kg in the older patients. Ther e was a more rapid clearance in the infants <2 mo of age (90 mL . kg(-1) . min(-2)) and infants 2 mo to 2 yr (92 mL . kg(-1) . min(-1)) than in the ot her groups (means, 46 to 76 mL . kg(-1) . min(-1)). The half-life was simil ar in all age groups, with means of 3.4 to 5.7 min. Seven subjects (17%) de veloped hypotension related to the remifentanil bolus. Remifentanil showed an extremely rapid elimination similar to that in adults. The fast clearanc e rates observed in neonates and infants, as well as the lack of age-relate d changes in half-life, are in sharp contrast to the pharmacokinetic profil e of other opioids. Remifentanil in a bolus dose of 5 mug/kg may cause hypo tension in anesthetized children.