Simultaneous LC-MS analysis of plasma concentrations of sildenafil, tadalafil, bosentan, ambrisentan, and macitentan in patients with pulmonary arterial hypertension.

Phosphodiesterase-5 (PDE-5) inhibitors and endothelin receptor antagonists (ERAs) are standard therapies for pulmonary arterial hypertension (PAH). The inter-individual variability of these pharmacokinetics is reported remarkably large, and therapeutic drug monitoring (TDM) can be useful to improve the likelihood of the desired therapeutic and safety outcomes. This study aimed to develop a LC-MS method to determine the concentrations of five PAH drugs (PDE-5 inhibitors: sildenafil and tadalafil, ERAs: bosentan, macitentan, and ambrisentan) from plasma samples using a simple process followed by a single mass spectrometric run, and to validate this approach through pharmacokinetic analyses in patients. A solid extraction method was used for sample preparation of the drugs from human plasma. The total run time for a single injection was within 10 min. The calibration curves for all drugs were linear, and the lower limits of quantitation were 1 (sildenafil), 2 (tadalafil), 5 (ambrisentan), and 10 ng/mL (bosentan, macitentan). The accuracy and precision values suggested that the assay had high accuracy and reliability. To prove the utility of this method, the plasma concentrations of the five PAH drugs were determined after their oral administration to nine PAH patients.