Rapid, Sensitive, and Quantitative LC/MS/MS Determination of Digitoxin and Digoxin in Plasma

Using a Simple Procedure for Simultaneous Cleanup of Phospholipids and Proteins

Introduction

Digitoxin and digoxin are cardiac glycosides derived from the digitalis purpurea (Foxglove) plant. They have been in use for centuries for treatment of various heart conditions. Because of their narrow therapeutic range and high toxicity, their levels in patients taking digitoxin or digoxin are monitored.^1-2 Immunoassay-based methods for digitoxin or digoxin exist, but are both time consuming and labor intensive. Moreover, the reported immunoassay methods are not selective toward digitoxin or digoxin due to the similarities in their chemical structures, which differ from each other in only one hydroxyl group (Figure 1). The present work was aimed at developing a rapid and selective LC/MS/MS method for the determination of digoxin and digitoxin in biological fluids. In addition, a simple sample cleanup technique for simultaneous removal of proteins and phospholipids using a zirconia-based sorbent, HybridSPE^®-PLus, was explored.