Pharmacokinetics of tafamidis, a transthyretin amyloidosis drug, in rats.

1. We characterized the pharmacokinetics of tafamidis, a novel drug to treat transthyretin-related amyloidosis, in rats after intravenous and oral administration at doses of 0.3-3 mg/kg. In vitro Caco-2 cell permeability and liver microsomal stability, as well as in vivo tissue distribution and plasma protein binding were also examined. 2. After intravenous injection, systemic clearance (CL), volumes of distribution at steady state (Vss) and half-life (T½) remained unaltered as a function of dose, with values in the ranges of 6.41-7.03 mL/h/kg, 270-354 mL/kg and 39.5-46.9 h, respectively. Following oral administration, absolute bioavailability was 99.7-104% and was independent of doses from 0.3 to 3 mg/kg. In the urine and faeces, 4.36% and 48.9% of tafamidis, respectively, were recovered. 3. Tafamidis was distributed primarily in the liver and not in the brain, kidney, testis, heart, spleen, lung, gut, muscle, or adipose tissue. Further, tafamidis was very stable in rat liver microsomes, and its plasma protein binding was 99.9%. 4. In conclusion, tafamidis showed dose-independent pharmacokinetics with intravenous and oral doses of 0.3-3 mg/kg. Tafamidis undergoes minimal first-pass metabolism, distributes mostly in the liver and plasma, and appears to be eliminated primarily via biliary excretion.

Development and validation of a liquid chromatography-tandem mass spectrometry method for the assay of tafamidis in rat plasma: Application to a pharmacokinetic study in rats.

Tafamidis is a first-in-class inhibitor of transthyretin amyloid fibril formation. It has been available in Argentina, Japan, and Mexico for the treatment of transthyretin amyloidosis in adult patients with early-stage symptomatic polyneuropathy. In this study, a rapid and sensitive liquid chromatography-tandem mass spectrometry method was developed and validated for the assay of tafamidis in rat plasma. The method was also assessed for its applicability to pharmacokinetic studies in rats. Tafamidis was extracted from rat plasma by the liquid-liquid extraction method using hydrochloric acid and ethyl acetate. A reversed-phase C18 column and a mobile phase consisting of 10mM ammonium formate and acetonitrile were used to achieve chromatographic separation. The flow rate for the mobile phase was set at 0.3mL/min. Tafamidis and 2-CBC, which was used as the internal standard (IS), were analyzed by multiple reaction monitoring in negative ESI mode at m/z transitions of 305.4→261.4 for tafamidis and 271.7→227.8 for the IS. The lower limit of quantification of tafamidis was obtained as 3ng/mL, and the calibration curve was linear over a concentration range of 3-3000ng/mL (R2>0.99). The validation parameters investigated, which were specificity, precision, accuracy, matrix effect, recovery, and stability, were well within acceptable limits. The method was successfully used for the evaluation of the pharmacokinetics of tafamidis in rats.