Development and validation of an UPLC-PDA method to quantify daptomycin in human plasma and in dried plasma spots.

Quantification of daptomycin in plasma samples may be useful in optimizing therapy especially in special patients' population. Nevertheless, therapeutic drug monitoring of daptomycin is still limited probably for the low number of laboratories which perform this analysis and for high shipment costs. We developed and validated a new UPLC-PDA method to quantify daptomycin in plasma and in dried plasma spots (DPS) collected on dried sample spots devices (DSSD). Daptomycin and quinoxaline, used as internal standard, were monitored at 262nm and 253nm, respectively. Daptomycin was extracted from plasma using acetonitrile and from DPS using an extraction solution (ethyl acetate-acetic acid-acetone-water; 50:20:20:10, v/v/v/v). Both assays were linear over the calibration range of 0.781 to 200µg/ml. Considering the method of extraction from plasma, mean intra and inter-day accuracy was -1.18% and -2.79%, respectively. Mean intra and inter-day precision was 7.91% and 9.22%, respectively. Regarding the extraction method from DPS, mean intra and inter-day accuracy was 2.21% and 2.41%, respectively. Mean intra and inter-day precision was 8.01% and 9.19%, respectively. Daptomycin in DPS was found to be stable for 7 days at room temperature (20-25°C) and for at least 30 days at 4°C. A statistically significant (p<0.001) linear correlation was found between daptomycin extracted from plasma and from DPS (r(2)=0.919). DPS represents a safe and cheap strategy to store and ship plasma samples. Thus, it is suited for pharmacokinetic studies and therapeutic drug monitoring of daptomycin in hospitals without a therapeutic drug monitoring laboratory.

Development and validation of a new method to simultaneously quantify triazoles in plasma spotted on dry sample spot devices and analysed by HPLC-MS.

OBJECTIVES: Therapeutic drug monitoring (TDM) of triazoles is widely used in clinical practice to optimize therapy. TDM is limited by technical problems and cost considerations, such as sample storage and dry-ice shipping. We aimed to develop and validate a new method to analyse itraconazole, posaconazole and voriconazole in plasma spotted on dry sample spot devices (DSSDs) and to quantify them by an HPLC system. METHODS: Extraction from DSSDs was done using n-hexane/ethyl acetate and ammonia solution. Samples were analysed using HPLC with mass spectrometry (HPLC-MS). Accuracy and precision were assayed by inter- and intra-day validation. The stability of triazoles in plasma spotted on DSSDs was investigated at room temperature for 1 month. The method was compared with a validated standard HPLC method for quantification of triazoles in human plasma. RESULTS: Mean inter- and intra-day accuracy and precision were <15% for all compounds. Triazoles were stable for 2 weeks at room temperature. The method was linear (r(2) > 0.999) in the range 0.031-8 mg/L for itraconazole and posaconazole, and 0.058-15 mg/L for voriconazole. High sensitivity was observed; limits of detection were 0.008, 0.004 and 0.007 mg/L for itraconazole, posaconazole and voriconazole, respectively. A high degree of correlation (r(2) > 0.94) was obtained between the DSSD method and the standard method of analysis. CONCLUSIONS: The method that we developed and validated to quantify triazoles in human plasma spotted on DSSDs is accurate and precise. It overcomes problems related to plasma sample storage and shipment, allowing TDM to be performed in a cheaper and safer manner.