Amlodipine interfere in serum albumin binding of loasrtan and its active metabolite losartan carboxylic acid (EXP- 1734): Contra-contemporary in vitro approaches

Abstract

The combination therapy of Losartan (LOS) and amlodipine (AMLO) has proven to be beneficial as compared to either individual drug monotherapy. Nonetheless, the mechanism of a beneficial effect is yet to be established. Conversely, displacement in protein binding may lead to change in free drug concentration. The selected analytes were effectively separated on Thermo β-basic C18 (100×4.6 mm, 5 µm) using mobile phase consisting of 20 mM monobasic potassium phosphate and 0.2 % TEA with acetonitrile and iso-propyl alcohol in gradient mode. The in vitro protein binding experiments were performed under simulated physiological conditions using ultrafiltration as drug-protein binding model and displacement interactions were observed. Amlodipine, losartan and LCA bind more than 95 % to recombinant human serum albumin (rHSA), when studied individually, whereas, protein binding of LCA and Losartan carboxylic acid (LCA) were not affected when spiked concomitantly with AMLO, whereas, binding of Amlodipine to rHSA was decreased by 15-20 % under similar conditions at supra pharmacological concentration level of LOS and LCA. In in-vitro experiments about three to five fold increase in free AMLO concentration was observed in ultrafiltrate in presence of LOS and LCA. The albumin binding capacity of all the analytes was reduced nearly seven to eight-fold in the case of Glycosylated Human serum albumin (Gly-HSA). The in vitro protein binding studies with Gly-HSA have shown alteration in the corresponding albumin binding of AMLO, LOS and LCA.