Simultaneous analysis of acyclovir and its metabolite using hydrophilic interaction liquid chromatography-tandem mass spectrometry

The antiviral drug acyclovir (ACV) may induce drug-induced neuropsychiatric symptoms as side effects. The detailed pathogenic mechanism remains unclear; however, it is hypothesized that 9-carboxymethoxymethylguanine (CMMG), a metabolite of ACV, is the causative compound. Therefore, the blood concentrations of ACV and CMMG should be analyzed in ACV toxicity studies. However, it is rare to find methods that can sufficiently separate the ACV and CMMG peaks during simultaneous analysis of both compounds. Therefore, we intended to develop a liquid chromatography-tandem mass spectrometry method with improved peak separation of analytes. Samples were deproteinized using methanol/acetonitrile solution (6:4, v/v). Analytes were separated on an InertSustain® Amide column (3 μm, 2.1 mm × 150 mm). The mobile phase consisted of acetonitrile/10 mM ammonium formate (5:95, v/v) (A) and acetonitrile/10 mM ammonium formate (95:5, v/v, pH 5.0) (B) and samples were eluted in the gradient mode. The separation of analytes was satisfactory and the peak shapes were good. Linear regression models weighted 1/x2 were obtained in the range of 0.25-10 μg/mL. The range of quality control (QC) bias was between 3.6% and 19.8%, and the within-run and between-run precisions of QC were within 13.5%. Recovery ranged from 83.6% to 103.7%, but ion suppression was observed. Samples from a patient with ACV encephalopathy were analyzed using this method. The resulting blood ACV and CMMG concentrations were 8.2 and 8.5 μg/mL, respectively. This method, with sufficient separation of ACV and CMMG, proved useful for use in ACV toxicity studies.