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Metabolism of (R)-[11C]verapamil in epilepsy patients
BMC Pharmacology volume 7, Article number: A23 (2007)
(R)-[11C]Verapamil (VPM) is a new positron emission tomography (PET) tracer to measure P-glycoprotein (P-gp)-mediated transport at the blood-brain barrier (BBB). Owing to the lack of a suitable reference region in brain that is devoid of P-gp, a metabolite-corrected arterial input function is required for quantitative analysis of VPM PET data . The aim of this study was to compare metabolism of VPM in epilepsy patients and healthy volunteers.
Selected arterial blood samples from 9 patients, who underwent VPM PET, were analyzed for radiolabeled metabolites by a previously described combined solid-phase extraction/HPLC assay .
VPM metabolism was significantly faster in patients as compared to healthy volunteers  (unchanged VPM at 60 min after injection: 26.1 ± 6.4 vs. 49.0 ± 13.4%, p < 0.05, t-test).
Faster metabolism of VPM in epilepsy patients may be caused by CyP450 enzyme induction by antiepileptic drugs. Based on these data caution is warranted when using an averaged arterial input function derived from healthy volunteers for the analysis of patient data. As radiolabeled metabolites of VPM are known to cross the BBB , different kinetic modeling parameters obtained in patients and healthy volunteers might be at least partly attributed to different rates of tracer metabolism rather than to differences in cerebral P-gp activity.
Lubberink M, Luurtsema G, van Berckel BN, Boellaard R, Toornvliet R, Windhorst AD, Franssen EJ, Lammertsma AA: Evaluation of tracer kinetic models for quantification of P-glycoprotein function using (R)-[11C]verapamil and PET. J Cereb Blood Flow Metab. 2007, 27: 424-433. 10.1038/sj.jcbfm.9600349.
Luurtsema G, Molthoff CF, Schuit RC, Windhorst AD, Lammertsma AA, Franssen EJ: Evaluation of (R)-[11C]verapamil as PET tracer of P-glycoprotein function in the blood-brain barrier: kinetics and metabolism in the rat. Nucl Med Biol. 2005, 32: 87-93. 10.1016/j.nucmedbio.2004.06.007.
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Abrahim, A., Luurtsema, G., Bauer, M. et al. Metabolism of (R)-[11C]verapamil in epilepsy patients. BMC Pharmacol 7, A23 (2007). https://doi.org/10.1186/1471-2210-7-S2-A23
- Positron Emission Tomography
- Healthy Volunteer
- Kinetic Modeling
- Antiepileptic Drug