Gas chromatographic-electron capture determination of 2,4'-dichlorodiphenylacetic acid from in-vitro adrenal transformations of mitotane and its analogs

A simplified method for therapeutic drug monitoring of mitotane by gas chromatography-electron ionization-mass spectrometry

Mitotane is a key drug for the treatment of adrenal cortical carcinoma. Due to its narrow therapeutic window, 14–20 μg/mL, monitoring its concentration is crucially important. In this study, a simplified method for measuring mitotane in plasma using gas chromatography‐electron ionization‐mass spectrometry (GC‐EI‐MS) was developed. Through deproteination and liquid–liquid extraction, mitotane and an internal standard (IS) were extracted from plasma samples. GC‐EI‐MS yielded retention times of 8.2 and 8.7 min, for mitotane and the IS, respectively, with a total run time of 12 min. Selectivity and intra‐/inter‐batch accuracy and precision analyses provided a lower limit of quantification of 0.25 μg/mL, and a calibration curve between 0.25 and 40 μg/mL had good linearity (coefficient of determination = 0.992). The matrix effect factor and percent recovery of the method had good precision. Additionally, long‐term sample stability was observed below 4°C. In a clinical setting, mitotane levels in plasma from an adrenal cortical carcinoma patient were within calibration range. Therefore, this simplified method can be applied to routine therapeutic drug monitoring of mitotane, which may contribute to improved treatment of adrenal cortical carcinoma.

Determination of mitotane (o,p-DDD) and its metabolites o,p-DDA and o,p-DDE in plasma by high-performance liquid chromatography

The adrenolytic agent mitotane (o,p'-DDD or 1,1-(o,p'-dichlorodiphenyl)-2,2-dichoroethane) is believed to be metabolically activated, resulting in the generation of reactive intermediates or the formation of o,p'-DDA. A new high-performance liquid chromatographic (HPLC) method for measurement of mitotane and two of its metabolites, o,p'-DDA (1,1-(o,p'-dichlorodiphenyl) acetic acid) and o,p'-DDE (1,1-(o,p'-dichlorodiphenyl)-2,2 dichloroethene), in plasma has been developed. Sample preparation involves precipitation of plasma proteins with acetone before chromatographic separation under isocratic conditions on a silica-based diphenyl column. Mitotane and metabolites are quantified by ultraviolet detection at 218 nm. Recoveries for the three compounds range between 99% and 110%, with between-day and within-day coefficients of variation <6% within the therapeutic range. Limits of detection are 0.5 microM and the assay is linear up to at least 800 microM for o,p'-DDA and 100 microM for mitotane and o,p'-DDE. The method has been evaluated using samples from three patients on mitotane therapy, revealing o,p'-DDA levels in plasma 3 to 10 times higher than the levels of the parent compound.