AbstractParicalcitol capsules are indicated for the prevention and treatment of secondary hyperparathyroidism in chronic kidney disease (CKD). Proton pump inhibitors are prescribed to CKD patients to treat gastroesophageal reflux. This was a single dose, crossover study evaluating the effect of omeprazole, change in gastric pH as a result thereof, on the pharmacokinetics (PK) of paricalcitol. Twenty‐six healthy subjects were administered paricalcitol capsules (16 µg) alone (regimen A), and following a single dose of OMP (40 mg) (regimen B), with a washout of at least 7 days. Plasma samples for paricalcitol concentrations were collected for 48 h post‐paricalcitol dose. The plasma paricalcitol concentrations were measured using an LC–MS/MS assay (LOQ=0.02 ng/ml) and paricalcitol pharmacokinetic parameters were estimated using non‐compartmental methods. The point estimates and the corresponding 90% confidence intervals for Cmax and AUC0‐∞ to evaluate paricalcitol–omeprazole interaction were 1.032 [0.920–1.158] and 1.041 [0.951–1.139], respectively. No significant differences in Tmax (regimen A: 2.9 h vs regimen B: 2.6 h) or t1/2 (6.83 h vs 6.6 h) between the regimens were observed. Hence, the co‐administration of omeprazole does not affect the PK of paricalcitol. Both regimens were well tolerated and no apparent differences among the regimens with respect to safety were observed. Copyright © 2007 John Wiley & Sons, Ltd.