Amantadine hydrochloride monitoring by dried plasma spot technique: High-performance liquid chromatography-tandem mass spectrometry based clinical assay.

Amantadine plasma concentrations correlate well with desired therapeutic effects and adverse outcomes; information on amantadine exposure could be useful when multiple amantadine clearance pathways are impaired or non-compliance is suspected. Micro-sampling strategies, like dried plasma spot, would be particularly useful because ambulatory patients that do not attend a clinic can easily sample a few drops of blood by themselves at the required time of the dosing interval. We developed and validated a dried-plasma-spot-based high performance liquid chromatography-tandem mass spectrometry assay to quantify amantadine. This assay met relevant validation requirements within a hematocrit range of 20-50% and was linear from 100 to 2000 ng/mL. Amantadine was stable in dried plasma spots for up to 21 days at room temperature, regardless of whether the dried plasma spot was protected from light or not. The correlation between paired dried and wet plasma concentrations was assessed in 52 patients. Deming regression coefficients between wet plasma and simultaneously pipetted dried plasma spots were used to predict plasma concentrations. Bland-Altman plots revealed a strong agreement between dried and wet plasma concentrations, supporting the clinical usefulness of dried plasma spots for amantadine monitoring with a self-sampling strategy at a convenient time and place for the patient.