Pharmacokinetic interactions of valsartan and hydrochlorothiazide: an open-label, randomized, 4-period crossover study in healthy Egyptian male volunteers

Abstract

Background: Co-administration of valsartan (VAL) and hydrochlorothiazide (HCT) has been used to regulate blood pressure. Compliance with a multiple medication regimen can be difficult for some patients; therefore, a combination of VAL + HCT tablets may be a suitable alternative.

Objective: This study was conducted to compare the rate and extent of absorption of VAL and HCT after oral administration as a fixed-dose combination (FDC) tablet and concomitant administration of the individual drugs under fasting conditions in healthy Egyptian subjects. The study was extended to investigate any potential interaction between VAL and HCT.

Methods: This study was conducted as an open-label, randomized study with 2 parts (parts I and II), with each part consisting of 4 single-dose treatment periods with a crossover design and 2-week washout periods. Blood samples were collected up to 48 hours postdose, and plasma was analyzed for VAL and HCT concentrations by using HPLC. The pharmacokinetic properties of each drug after co-administration of VAL and HCT were compared with those of each drug administered alone. Tolerability was assessed by physical examination and verbally questioning subjects regarding their well-being and any feelings of discomfort. All events reported by the subjects were recorded in adverse-event forms.

Results: Forty-eight healthy subjects were enrolled (24 in each part), and all subjects completed the study. None of the participants showed any sign of adverse drug reactions during or after the completion of the study. Statistical analysis confirmed that the 90% CIs for AUC and Cmax of VAL/HCT FDC and VAL + HCT were within the commonly accepted bioequivalence range of 0.8 to 1.25. As a result, from an in vivo pharmacokinetic perspective, 1 FDC tablet could be considered interchangeable in medical practice with the 2 individual reference tablets. However, the 90% CIs between VAL alone and when administered with HCT, either as FDC or concomitantly, indicated the presence of an interaction between VAL and HCT, which would significantly decrease the systemic exposure and intensity of VAL absorption. The co-administration of HCT with VAL decreased the AUC and Cmax of HCT nonsignificantly compared with administration of HCT alone.

Conclusions: Both VAL/HCT FDC and VAL + HCT were well tolerated. The safety/efficacy profile of VAL + HCT co-administration therapy could be extended to the VAL/HCT FDC tablet. The interaction of HCT with other angiotensin-receptor blockers should be investigated to determine whether this interaction is limited to VAL or if other angiotensin-receptor blockers have the same pharmacokinetic interactions. Further studies are necessary to determine the role of efflux and influx transporters on VAL and HCT disposition and pharmacokinetics.