Validation of a quantitative LC-MS/MS Dried Blood Spot method for cyclosporin A in blood

A rapid, selective and sensitive bioanalytical method was developed and validated for cyclosporin A (CsA) in cat blood samples using dried blood spot (DBS) coupled with high pressure liquid chromatography hyphenated to positive electrospray tandem mass spectrometry (HPLC-ESI-MS/MS). CsA was quantified using a structural analog cyclosporin D (CsD) as internal standard in multiple reaction monitoring mode (MRM) using the transitions 1220→1203 for CsA and 1234→1217 for CsD. A 5-μL blood aliquot was spotted onto a DBS card, then after a drying step, blood spots were punched out from the cards and extracted with MeOH before injection into a LC-MS/MS system. The linear range of the method was 5-2000 ng/mL, with accuracy and precision within the FDA acceptance criteria (i.e., ±15% and ±20% for the lowest level). In the study presented herein a comparison was made between this new methodology, based on the use of DBS, and a previously developed solid phase extraction (SPE) procedure, applied to blood samples from a cat pharmacokinetic study. Good correlation (r(2)=0.97) was demonstrated between the data obtained with the two methods. The DBS methodology revealed to be cheaper, faster, less solvent-consuming and requiring less blood volume from animals than the previous SPE method. Thus, the proposed HPLC-ESI-MS/MS method, based on DBS, has demonstrated to be a suitable and advantageous approach for the analysis of CsA in cat blood.