Drug Metabolism and Bioanalysis Letters Formerly: Drug Metabolism Letters - Online First

Efinaconazole is a topical antifungal medication that is effective against fungal infections of the toenails. In addition, due to its application on the skin, minimal systemic absorption takes place on the epidermic layer, which leads to the availability of lower-level concentration in the bloodstream. Although several reported methods in the literature describe the quantification of Efinaconazole using conventional techniques like HPTLC and HPLC, these methods lack the necessary sensitivity and selectivity to be directly applied for quantification in biological samples.

Current research work aimed to develop a rapid, specific, selective, and sensitive method using plasma as one of the biological samples for quantification of Efinaconazole (EZ) in the presence of Fluconazole (FZ) as an internal standard by tandem mass spectrometry (LC-MS/MS).

Chromatographic separation was achieved with a Thermo Hypersil Gold (100 mm x 2.1mm, 1.9 µm) UPLC column using a mobile phase composed of 20% formic acid-water (0.1%) and 80% methanol. Liquid-liquid extraction (LLE) was employed for sample preparation. Efinaconazole and the internal standard were detected using the heated electrospray ionization (HESI) technique in parallel reaction monitoring (PRM) mode.

The developed method displayed a linearity range of 1 to 2000 pg/mL (0.001-2 ng/mL). Precision and accuracy for the lower limit of quantitation, low, mid, and high-quality control (QC) levels demonstrated a variance of less than 5% and an accuracy of 99 to 103%. Long-term stability was confirmed under various conditions, including storage in an auto-sampler, at room temperature, in a deep freezer, and after freeze-thaw cycles.

The validated LC-MS/MS method has exceptional sensitivity, specificity, selectivity, rapid analysis, minimal requirement of sample quantity, wide dynamic range of concentration, robustness, and reproducibility, making it an indispensable tool, especially in fields of in vitro Permeation Testing (IVPT), in vitro Release Testing (IVRT), Pharmacokinetic, Toxicology, Clinical studies, and in drug development program for the quantification of Efinaconazole