ANALYSIS OF TOPIRAMATE AND ITS METABOLITES IN PLASMA AND URINE OF HEALTHY SUBJECTS AND PATIENTS WITH EPILEPSY BY USE OF A NOVEL LC-MS ASSAY
Abstract number :
1.264
Submission category :
Year :
2003
Submission ID :
2210
Source :
www.aesnet.org
Presentation date :
12/6/2003 12:00:00 AM
Published date :
Dec 1, 2003, 06:00 AM
Authors :
Malka Britzi, Stefan Soback, Nina Isoherranen, Rene[apos] H. Levy, Emilio Perucca, Dennis R. Doose, Bruce E. Maryanoff, Meir Bialer Pharmaceutics, School of Pharmacy, Faculty of Medicine, Hebrew University, Jerusalem, Israel; National Residue Laboratory,
No assay is currently available for topiramate (TPM) metabolites. Therefore, the aim of this study was to develop novel liquid chromatography-mass spectrometry (LC-MS) method for the quantification of TPM and its metabolites: 10-hydroxy topiramate (10-OH-TPM), 9-OH-TPM, 4,5-O-desisopropylidene topiramate (4,5-diol-TPM) and 2,3-diol-TPM in plasma and urine.
The method utilizes 0.5 mL of plasma or 1 mL of urine that is extracted with diethyl ether and analyzed by LC-MS. Positive ion mode detection enables tandem mass spectrometric identification of the above four compounds. Linaer calibration curves of TPM, 4,5-diol-TPM, 9-OH-TPM and 10-OH-TPM in plasma and urine were prepared and validated over the concentration range of 0.625-40 mg/mL, using TPM-d[sub]12[/sub] as an internal standard.
Accuracy and precision ranged in urine between 83-114% and 4-13% (%CV), respectively and in plasma between 82-108% and 6-13%, respectively. The applicability of the assay was evaluated by analyzing plasma samples from a healthy subject who received TPM (200 mg) and urine samples from patients with epilepsy, treated with TPM alone or with other antiepileptic drugs. TPM plasma concentration ranged between 0.6 and 4.3 mg/L. TPM and 10-OH TPM urine concentrations ranged from 20 to 300 mg/L and from 1 to 50 mg/L, respectively. The metabolites 4,5-diol-TPM and 9-OH-TPM were quantifiable only in four patients (out of 11 total). An unidentified peak in the chromatograms obtained from patients[rsquo] urine was attributed to 2,3-diol-TPM (2,3-O-desisopropylidene topiramate). Due to the similar MS/MS spectrum with 4,5-diol-TPM, its calibration curves were utilized for the quantification of 2,3-diol-TPM. The 2,3-diol-TPM/TPM concentration ratio in patients[rsquo] urine ranged from 0.05 to 0.51 and the 10-OH-TPM/TPM ratio ranged from 0.02 to 0.17.
A novel LC-MS method for the assay of TPM and four of its metabolites was developed. Its utilization showed that the method was suitable for analysis of TPM and its metabolites in clinical samples. Two quantitatively significant TPM metabolites (10-OH-TPM and 2,3-diol-TPM) and two quantitatively minor metabolites (9-OH-TPM and 4,5-diol-TPM) were quantified in urine samples of patients with epilepsy.
[Supported by: An unrestricted grant from Johnson [amp] Johnson Pharmaceutical Research [amp] Development, L.L.C., Raritan, NJ, USA.]