Pharmacokinetics of fentanyl in patients of different ages undergoing non-cardiac surgery

Objective The purpose of this study was to determine the effects of different ages on pharmacokinetics of fentanyl in patients undergoing non-cardiac surgery. Thus fentanyl may be used reasonally and safely in clinical practice. Methods Twenty-four patients undergoing abdominal surgery were divided into 3 age groups. Each group had eight patients. The age of the patients in group Ⅰ ranged from 8-13 years, in group Ⅱ 18-30 years and in group Ⅲ 60-72 years. Blood samples were obtained from radial artery 1, 2, 5, 10, 20, 30, 60, 180 and 240 min following a bolus injection of fentanyl 5μg· kg-1 . Plasma fentanyl concentration was determined by GC-MS methods. The pharmacokinetic p arameters were calculated using 3P87 computer program. Results Plasma fentanyl concentration reached its peak rapidly following a bolus injection. The plasma concentration versus time curve was fitted to three-compartment open modle using triexponential equation. Although the patients of different age groups received equivalent dose of fentanyl (5μg· kg-1 ), plasma concentration was higher in elderly patients. This resulted from a prolonged t1/2 β in the elderly patients (group Ⅲ ). Vc and Vd increased significantly in group Ⅱ and Ⅲ patients (P＜0.05). t1/2π and t1/2α were similar in three groups (P＞0.05). CL decreased markedly in group Ⅲ (P＜0.05). Significant correlationswere found between age and both t1/2 β and CL(P＜0.05). Conclusions Use of fentanyl in children may follow the guidelines suggested for adults. In elderly the dose of fentanyl should be reduced to some degree because of prolonged t1/2 β and decreased CL.