Simultaneous quantification of anidulafungin and caspofungin in plasma by an accurate and simple liquid chromatography tandem mass-spectrometric method

INTRODUCTION: Echinocandins are a valuable addition for the treatment of invasive fungal infections, as they are efficacious, demonstrate low toxicity, and have limited drug-drug interactions. In specific clinical situations when altered pharmacokinetics can be expected or dosing guidelines are conflicting, it may be useful to measure concentrations. For this purpose, a liquid chromatography tandem mass-spectrometric method to measure anidulafungin and caspofungin in ethylenediaminetetraacetic acid plasma was developed.

METHODS: The method was developed on a Thermo Fisher TSQ Quantum LC-MS/MS. For separation, a BetaBasic C4 (100 mm × 3.0 mm; 5 μm) analytical column was used. Sample preparation consisted of protein precipitation directly in the autosampler vial. The internal standard aculeacin A is structurally related, not used in humans, and commercially available. The method was validated according to the guidelines for bioanalytical method validation of the Food and Drug Administration.

RESULTS: The method was accurate (bias ranging from -3.0% to 1.9%) and precise (within-run and between-run coefficients of variation of 2.2% to 7.7% and 1.6% to 9.0%, respectively). All calibration curves were linear over a range of 0.5-10.0 mg/L for anidulafungin and 0.1-20.0 mg/L for caspofungin, and if necessary, samples can be diluted 10-fold. The samples were stable for 3 freeze-thaw cycles, with a bias ranging from 0.6% to 11%. The maximum bias from the worst storage condition, 72 hours at room temperature, was -14.7%. In patient samples, anidulafungin peak concentrations ranged from 2.8 to 8.6 mg/L (n = 20) and trough concentrations ranged from 1.0 to 4.7 mg/L (n = 79). The measured caspofungin concentrations ranged from 1.9 to 7.3 mg/L (n = 20).

CONCLUSIONS: The method developed has a straightforward sample preparation and uses a structural analog as the internal standard. This method has been applied successfully for the measurement of anidulafungin and caspofungin concentrations in patient samples, both for clinical practice and for research.