Absorption
No food effect study was conducted with 30 mcg and 60 mcg doses of RAYALDEE. However, a food effect study with a supratherapeutic dose of 450 mcg in healthy subjects showed an approximately 5-fold increase in maximum serum calcifediol concentration (Cmax) and a 3.5-fold increase in AUC0-t when RAYALDEE was administered with a high fat, high calorie meal compared to fasting.
Exposure to calcifediol increased proportionally over the dose range of 30 to 90 mcg following repeated daily administration of RAYALDEE at bedtime to subjects with secondary hyperparathyroidism, chronic kidney disease and vitamin D insufficiency. Steady-state levels of serum total 25-hydroxyvitamin D are reached after approximately 3 months [see Clinical Studies (14)].
Distribution
Calcifediol is extensively bound to plasma proteins (>98%). The mean apparent volume of distribution is 8.8 L in healthy subjects following a single oral dose of RAYALDEE, and 30.1 L in subjects with stage 3 or 4 chronic kidney disease following repeated dosing.
Elimination
The mean elimination half-life of calcifediol is approximately 11 days in healthy individuals following a single dose of RAYALDEE, and approximately 25 days in patients with stage 3 or stage 4 chronic kidney disease following repeated once daily dosing.
Metabolism
Production of calcitriol from calcifediol is catalyzed by the 1-alpha-hydroxylase enzyme, CYP27B1, located in the kidney and other tissues. CYP24A1, located in all vitamin D-responsive tissues, catabolizes both calcifediol and calcitriol to inactive metabolites.
Excretion
Excretion of calcifediol occurs primarily through the biliary fecal route.
Specific Populations
Age, Gender and Race
Based on a population pharmacokinetic analysis, age, gender and race had no meaningful impact on steady-state concentrations of calcifediol following RAYALDEE administration.
Hepatic Impairment
The pharmacokinetics of RAYALDEE have not been investigated in patients with hepatic impairment.
Renal Impairment
Based on the population pharmacokinetics analysis, there was no meaningful difference in calcifediol steady-state concentrations following repeated RAYALDEE administration in patients with stage 3 or stage 4 chronic kidney disease.