Abstract
ORKAMBI (ivacaftor-lumacaftor [LUMA]) and KALYDECO (ivacaftor; IVA) are two new breakthrough cystic fibrosis (CF) drugs that directly modulate the activity and trafficking of the defective CFTR underlying the CF disease state. Currently, no therapeutic drug monitoring assays exist for these very expensive, albeit, important drugs. In this study, for the first time HPLC and LC-MS methods were developed and validated for rapid detection and quantification of IVA and its major metabolites hydroxymethyl-IVA M1 (active) and IVA-carboxylate M6 (inactive); and LUMA in the plasma and sputum of CF patients. With a mobile phase consisting of acetonitrile/water:0.1% formic acid (60:40v/v) at a flow rate of 1mL/min, a linear correlation was observed over a concentration range from 0.01 to 10μg/mL in human plasma (IVA R2>0.999, IVA M1 R2>0.9961, IVA M6 R2>0.9898, LUMA R2>0.9954). The assay was successfully utilized to quantify the concentration of LUMA, IVA, M1 and M6 in the plasma and sputum of CF patients undergoing therapy with KALYDECO (IVA 150mg/q12h) or ORKAMBI (200mg/q12h LUMA-125mg/q12h IVA). The KALYDECO patient exhibited an IVA plasma concentration of 0.97μg/mL at 2.5h post dosage. M1 and M6 plasma concentrations were 0.50μg/mL and 0.16μg/mL, respectively. Surprisingly, the ORKAMBI patient displayed very low plasma concentrations of IVA (0.06μg/mL) and M1 (0.07μg/mL). The M6 concentrations (0.15μg/mL) were comparable to those of the KALYDECO patient. However, we observed a relatively high plasma concentration of LUMA (4.42μg/mL). This reliable and novel method offers a simple and sensitive approach for therapeutic drug monitoring of KALYDECO and ORKAMBI in plasma and sputum. The introduction of the assay into the clinical setting will facilitate pharmacokinetics/pharmacodynamic analysis and assist clinicians to develop more cost effective and efficacious dosage regimens for these breakthrough CF drugs.