The purpose of this study was to develop an ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method of 22 antiepileptics for routine therapeutic monitoring. The antiepileptics used in the analyses were carbamazepine, carbamazepine-10,11-epoxide, clobazam, N-desmethylclobazam, clonazepam, diazepam, N-desmethyldiazepam, ethosuximide, felbamate, gabapentin, lamotrigine, levetiracetam, N-desmethylmesuximide, nitrazepam, phenobarbital, phenytoin, primidone, tiagabine, topiramate, valproic acid, vigabatrin and zonisamide. After protein precipitation of 50 μL plasma with methanol, the supernatant was diluted with water or was evaporated to dryness and reconstituted with mobile phase in the case of benzodiazepines. Separation was achieved on an Acquity UPLC BEH C₁₈ column with a gradient mobile phase of 10 mm ammonium acetate containing 0.1% formic acid and methanol at a flow rate of 0.4 mL/min. An Acquity TQD instrument in multiple reaction monitoring mode with ion mode switching was used for detection. All antiepileptics were detected and quantified within 10 min, with no endogenous interference. All the calibration curves showed good linearity in the therapeutic range (r² < 0.99). The precision and accuracy values for intra- and inter-assays were within ±15% except for phenobarbital and tiagabine. A good correlation was observed between the concentration of clinical samples measured by the new method described here and the conventional methods. The values of carbamazepine and phenytoin by UPLC-MS/MS were lower than those detected by the immunoassays, which might be caused by the cross-reaction of antibodies with their metabolites. In conclusion, we developed a simple and selective UPLC-MS/MS method suitable for routine therapeutic monitoring of antiepileptics.

Monitoring of pharmacodynamics in addition to pharmacokinetics is one of strategies to individualize mycophenolate mofetil therapy. The purpose of this study was to develop sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods for evaluation of the pharmacokinetics and pharmacodynamics of mycophenolic acid (MPA). Concentrations of mycophenolic acid glucuronide (MPAG), mycophenolic acid acyl-glucuronide, as well as unbound MPA and MPAG, were determined, and inosine-5'-monophosphate dehydrogenase activity was calculated by measuring concentrations of produced xanthosine-5'-monophosphate (XMP) and intracellular adenosine-5'-monophosphate after incubation of peripheral blood mononuclear cell (PBMC) lysates. A metal-free Mastro(TM) column and two gradient patterns were used to improve the quantification limit of XMP to 0.1 μM. In the clinical MPA concentration range, the linearity of the calibration curve, inter- and intra-day precision and accuracy satisfied the relevant US Food and Drug Administration guidelines. The MPA concentrations in hematopoietic stem cell transplant (HSCT) patients determined by the enzyme assay and the present LC-MS/MS method showed a good correlation (r(2) = 0.95, p < 0.001). In this study, we report sensitive and validated LC-MS/MS methods to evaluate the pharmacokinetics and pharmacodynamics of MPA, which are sufficiently sensitive to assess small quantities of PBMC lysates collected shortly after HSCT.

Oral clearance allometrically related with body weight and eGFR can well predict the routine therapeutic drug monitoring data from pediatric to aged patients with varying renal function. Dosage adjustments based on renal function are effective in controlling the trough and peak concentrations in similar ranges.