Simultaneous measurement of cyclosporin A and tacrolimus from dried blood spots by ultra high performance liquid chromatography tandem mass spectrometry

Cyclosporin A (CsA) and tacrolimus are immunosuppressant drugs principally used in solid organ transplant recipients. Therapeutic drug monitoring (TDM) of both drugs is essential to avoid toxicity related to overdosage, and transplant rejection from underdosage. This necessitates frequent hospital visits to phlebotomy services. Capillary blood sampling onto dried blood spots (DBS) provides numerous advantages to venous whole blood sampling, including the ability for patients to send DBS to the laboratory by post, significantly reducing the number of unnecessary hospital visits. We have developed a novel, simple and rapid method for the extraction and simultaneous UPLC-MS/MS measurement of both CsA and tacrolimus from DBS. The extraction method involved a simple 30 min hot solvent extraction with ultrasonication. Extract (10 μL) was injected onto a Waters Acquity UPLC column filter unit security frit, coupled to a Waters Acquity BEH C18 UPLC column, with methanolic mobile phase gradient elution. Eluant was connected to a Waters Quattro Premier XE tandem mass spectrometer operating in ES+ mode. We detected multiple reaction monitoring (MRM) transitions of m/z 1220 > 1203 and 1231.9 > 1215.1 for CsA and d12 CsA respectively which co-eluted at 1.30 min, and 821.6 > 768.5 and 809.6 > 756.5 for tacrolimus and ascomycin respectively which co-eluted at 1.17 min. Ion suppression was negligible. Mean recovery was 95.5% for CsA and 92.8% for tacrolimus. Limit of detection and limit of quantitation were both 8.5 μg/L for CsA, and 0.5 and 2.3 μg/L respectively for tacrolimus. The assay was linear up to 1500 μg/L for CsA (r2 = 0.9999), and up to 50 μg/L for tacrolimus (r2 = 0.9994). Mean intra assay imprecision, inter assay imprecision and bias were all <10% for both CsA and tacrolimus. DBS were stable for at least 14 days at room temperature. Comparison of the DBS UPLC-MS/MS method and the routine venous whole blood LC-MS/MS assay demonstrated good agreement between the two methods for both drugs. We have developed a simple and robust method for the extraction and simultaneous measurement of CsA and tacrolimus from DBS. The method will allow TDM of transplant recipients to proceed at home using capillary blood sampling.