Cross-Reactivity Assessment of Carbamazepine-10,11-epoxide, Oxcarbazepine, and 10-Hydroxy-Carbazepine in Two Automated Carbamazepine Immunoassays: PETINIA and EMIT 2000

Abstract

This study was conducted to compare the cross-reactivity of two commercially available carbamazepine (CBZ) immunoassays (PETINIA and EMIT 2000) with carbamazepine-10,11-epoxide (CBZ-E), the active metabolite of CBZ. Oxcarbazepine (OCBZ) and its main metabolite 10-hydroxy-carbazepine (HCBZ) have a chemical structure closely related to that of CBZ. The cross-reactivities of these two drugs were also investigated. In the first part of the study, Lyphocheck blank human serum and Chemonitor quality controls (containing CBZ without CBZ-E) were spiked with variable amounts of CBZ-E. The apparent CBZ levels were measured by PETINIA and EMIT 2000 methods. The interference from OCBZ and HCBZ was directly assessed by measuring the apparent CBZ levels in Chromsystems Trileptal quality controls (containing OCBZ and HCBZ). In the second part of the study, the CBZ levels of serum samples from 49 patients, including 2 patients with massive CBZ ingestion, were measured by immunoassays and compared with a high-pressure liquid chromatography (HPLC) reference technique allowing the simultaneous measurement of CBZ and CBZ-E. The antibody used in the PETINIA assay cross-reacts (about 90%) with CBZ-E. In one case of CBZ poisoning (CBZ and CBZ-E levels measured by HPLC were 26.2 and 18.2 mg/L, respectively), CBZ level measured by PETINIA was falsely elevated (42.5 mg/L). In contrast, the specificity of EMIT 2000 was satisfactory (29.5 mg/L). The two immunoassays tested showed low cross-reactivity with OCBZ and HCBZ. In conclusion, it appears that the CBZ-E metabolite present in samples can falsely increase CBZ levels measured by the PETINIA assay.

Carbamazepine is an inhibitor of histone deacetylases

“…CBZ is metabolized extensively in vivo. CBZE is the major metabolite that can be found in similar concentrations in serum as the parent compound and contributes to its biologic activity (Parant et al, 2003). CBZE was found in our studies to inhibit HDAC activity with the same potency as CBZ.…”

“…CBZE is the major metabolite of CBZ in vivo and is found in patients' serum at comparable concentrations as the parent compound (Parant et al, 2003). When preparing a 10 mM stock, we found that adding premixed HBC solution in H2O to CBZE powder yielded a suspension that was only partially active in our assays and formed a fine precipitate.…”

Effects of Major Transporter and Metabolizing Enzyme Gene Polymorphisms on Carbamazepine Metabolism in Chinese Patients with Epilepsy

“…In humans, more than 90% CBZE is subsequently metabolized by mEH to inactive CBZD after CBZ epoxidation [49,50]. The steady-state trough concentration of CBZE is 15-20% of the parent drug in CBZ monotherapy [51], and mEH plays the most important role in CBZE biotransformation and detoxication. CBZD:CBZE ratio is a more appropriate index for reflecting mEH activity in vivo than CBZ concentration.…”

Estimation of Carbamazepine and Carbamazepine-10,11-Epoxide Concentrations in Plasma Using Mathematical Equations Generated With Two Carbamazepine Immunoassays

“…18 It is also documented that valproic acid increases the incidence of carbamazepine-related toxic effects as well, due to accumulation of the epoxide metabolite in the plasma, despite total plasma carbamazepine concentrations within the therapeutic range. 14 The need for determination of carbamazepine and epoxide concentrations is clinically significant for select patient populations and clinical scenarios, wherein accumulation of the active epoxide level is likely. Although there are immunoassays that will cross-react with the epoxide metabolite to account for the amount of total active drug in circulation, there are currently no immunoassays for determination of the epoxide metabolite concentration independent of the carbamazepine concentration.…”