SummaryThe pharmacokinetics and haemodynamic response after an intravenous bolus injection of clonidine (2.5 μg·kg−1) were investigated in paediatric patients. Plasma levels of clonidine were determined by radioimmunoassay in eight ASA 1 paediatric patients (age: 33 months (SD 13), weight: 15.1 kg (SD 3.4), body surface area: 0.625 m2(SD 0.109)). A considerably shorter terminal half‐life (mean 6.13 h (SD 1.33), harmonic mean: 5.55 h, 95 confidence interval 4.60–7.63), a smaller distribution volume (0.96 1·kg−1(SD 0.43)) and a higher total body clearance (4.85 ml·kg−1min−1(SD 1.00)) were found in comparison with previously reported adult studies. The haemodynamic response was investigated during isoflurane anaesthesia in twelve ASA 1 children (age: 31 months (SD 11), weight: 14.4 kg (SD 3.1)) premedicated with rectal midazolam and atropine. A significant reduction in mean arterial blood pressure (MABP) was observed (P= 0.0032). The MABP was found to be reduced by 26.3 (SD 13.6) compared with baseline and the time for 75 of the expected blood pressure reduction to occur was 21.3 min (SD 25.6). A consistent finding in all patients was a harmonic undulation of the blood pressure implying a dampened sine wave response. A small but significant decrease in heart rate (127 bpm (SD 19)vs119 bpm (SD 20),P= 0.006) was observed immediately after injection following which the heart rate gradually returned to the previous baseline. The observed changes in heart rate and blood pressure responses were of a moderate magnitude. The use of clonidine as a premedicant or adjunct to general anaesthesia in children appears to be appropriate from both a pharmacokinetic and haemodyn
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