Fig. 4

Plasma fentanyl concentration after intravenous and transdermal administration in GK and Wistar rats. Fentanyl citrate injection (10 µg/kg body weight as fentanyl) was administered intravenously to GK (open circle) and Wistar (closed circle) rats (A). Fentanyl citrate formulation (160 µg as fentanyl) was applied to the lateral abdominal skin and the formulation was removed at 24 h (B). Data are expressed as mean ± S.D. (n = 5)