An 84 kg male is prescribed a 75 ug/hr transdermal patch of fentanyl (MW= 336.71: logP= 4) to treat chronic pain. The size of the patch is 42 cm2 and he wears it for 48 hours without taking the patch off. Fentanyl has a half-life of 3.7 hours, a volume of distribution of 3.6 L/kg, and a dermal permeability of about 1.1 x 10-3 cm/sec.

a) Estimate the absorption rate during the exposure period assuming the blood concentration is much lower than the skin concentration (i.e., take the blood level to be zero in the skin absorption equation). Use 0.0012 g/L for Cskin.

b) Estimate how long it takes after exposure begins for the groundskeepers plasma fentanyl levels to reach a therapeutic plasma drug concentration of 9 ng/L.

c) Estimate the maximum plasma fentanyl concentration that will occur in the patient while wearing the patch.