Hydroxyzine and Metabolites as a Source of Interference in Carbamazepine Particle-Enhanced Turbidimetric Inhibition Immunoassay (PETINIA)

Effectiveness of a Reliable Toxicological Analysis for a Correct Diagnosis of Acute Intoxication in Pediatrics: 2-Year Experience of an Analytical Toxicological Laboratory

OBJECTIVES

This study aimed to assess the role of the laboratory of toxicology as a support for a correct diagnosis of intoxication through the application of a reliable analytical approach, critically designed to meet pediatric needs.

METHODS

Data collected from 360 cases of suspected intoxications in pediatric patients (aged 1 day to 17 years) during the period 2018 to 2019 are presented. Toxicological analyses were performed through different techniques (immunoassay and chromatography) with parameters (limit of detection and cut-off) adjusted according to pediatric needs to produce reliable toxicological data for a wide number of prescription drugs, drugs of abuse, and poisons.

RESULTS

We present results about (1) agents involved in suspected poisonings and the methods adopted for a definite analytical diagnosis, (2) the assessment of the concordance of results for analyses proceeded by different techniques, and (3) the percentage of agreement between analytical result and clinical suspicion.

CONCLUSIONS

An analytical approach critically designed to minimize misinterpretation of laboratory data and able to provide reliable results for a wide number of substances in a time compatible with the urgency represents a useful support for a correct diagnosis of intoxication in pediatrics.

Heterogeneous and homogeneous immunoassays for drug analysis

Immunoassays are very useful techniques to perform screening and semi-quantitative analysis of hundreds of different xenobiotics. Small sample volumes are required and pretreatment is usually unnecessary (e.g., homogeneous immunoassays). Fully automated and high-throughput systems are available, which help physicians to take timely decisions. However, immunoassays do suffer from interference from both endogenous and exogenous factors that limit their application in quantitative analysis. These assays use different labels (e.g., colorimetric, fluorescent, chemiluminescent or electrochemiluminescent) and different methods for generating and measuring signals, but the basic principles are usually similar. This review outlines the practical aspects of immunoassays in bioanalysis and describes their application in clinical chemistry for xenobiotic analysis, namely medicines and drugs of abuse.

Impact of interferences including metabolite crossreactivity on therapeutic drug monitoring results

Therapeutic drug monitoring is an integral part of services offered by toxicology laboratories because certain drugs require routine monitoring for dosage adjustment to achieve optimal therapeutic response and avoid adverse drug reactions. Immunoassays are widely used for therapeutic drug monitoring. However, immunoassays suffer from interferences from both exogenous and endogenous compounds including metabolites of the parent drug. Digoxin immunoassays are affected more commonly than any other immunoassays used for therapeutic drug monitoring. Digoxin immunoassays are affected by endogenous digoxin-like immunoreactive substances and exogenous compounds such as various drugs, certain herbal supplements, and Digibind. Carbamazepine is metabolized to carbamazepine 10, 11-epoxide, and the crossreactivity of this metabolite with carbamazepine immunoassay may vary from 0% to 94%. Immunoassays used for measuring concentrations of tricyclic antidepressants are affected by tricyclic antidepressant metabolites and by a number of other drugs. Immunoassays for immunosuppressants are also subjected to significant interferences from metabolites, and liquid chromatography combined with mass spectrometry or tandem mass spectrometry is recommended for therapeutic drug monitoring of immunosuppressants. However, liquid chromatography combined with mass spectrometry may also suffer from interferences, for example, due to ion suppression or from isobaric ions.

Cetirizine as pH-dependent cross-reactant in a carbamazepine-specific immunoassay

High performance liquid chromatography (HPLC) was hyphenated with a previously reported carbamazepine-specific enzyme-linked immunosorbent assay (ELISA) as a screening approach to water analysis in order to identify possible interferences from transformation products. Treated wastewater was analysed and three substances were recognized by the antibody besides carbamazepine: the metabolites 10,11-dihydro-10,11-epoxycarbamazepine and 2-hydroxycarbamazepine plus the structurally not obviously related antihistamine cetirizine. The molar cross-reactivity against cetirizine was found to be pH-dependent and assessed to be 400% at pH 4.5 and 22% at pH 10.5. Performing the ELISA at pH 10.5 greatly improved the accuracy when carbamazepine was determined in surface and wastewater samples.

Analytical performance evaluation of ADVIA Chemistry Carbamazepine_2 assay: minimal cross-reactivity with carbamazepine 10, 11-epoxide and none with hydroxyzine or cetirizine

Carbamazepine is an anticonvulsant requiring routine therapeutic drug monitoring. Recently, Siemens Healthcare Diagnostic Division released a new carbamazepine assay: ADVIA Chemistry Carbamazepine_2 (Carbamazepine_2) for application on ADVIA analyzers. We evaluated the analytical performance of this assay as well as its potential cross-reactivities with carbamazepine 10, 11-epoxide, hydroxyzine, and cetirizine. The within-run and between-run precisions of the Carbamzepine-2 assay were <6% and limit of detection was 0.5 microg/ml using ADVIA 1800 analyzer. The assay was linear up to a carbamazepine concentration of 20.0 microg/ml. The new method compared well with a widely used carbamazepine EMIT 2000 assay on the Hitachi 917 analyzer. Using 75 patients' specimens (where carbamazepine concentrations varied from 0.5 to 21.7 microg/ml) and carbamazepine EMIT 2000 as the reference method (x-axis), we observed the following regression equation: y=1.04 x+0.32 (r=0.99). The new carbazepine_2 method was not affected by a hemoglobin concentration of 1,000 mg/dl, conjugated or unconjugated bilirubin concentration of 60 mg/dl, and triglyceride concentration of 1,000 mg/dl. In addition, this assay showed no cross-reactivity with hydroxyzine or cetirizine and demonstrated minimal cross-reactivity with carbamazepine 10, 11-epoxide. We conclude that the ADVIA Chemistry carbamazepine_2 assay has adequate precision and accuracy for routine therapeutic drug monitoring of carbamazepine in clinical laboratories.

Pharmacokinetics in special populations

Pharmacokinetics are typically dependent on a variety of physiological variables (e.g., age, ethnicity, or pregnancy) or pathological conditions (e.g., renal and hepatic insufficiency, cardiac dysfunction, obesity, etc.). The influence of some of these conditions has not always been thoroughly assessed in the clinical studies of antiallergic drugs. However, the knowledge of the physiological grounds of the pharmacokinetics can provide some insight for predicting the potential alterations and guiding the initial prescription strategies. It is important to recognize that both pharmacokinetic and pharmacodynamic differences between populations should be considered. The available information on drugs used for the therapy of allergic diseases is reviewed in this chapter.

Turbidimetric carbamazepine immunoassay on the ADVIA 1650 and 2400 analyzers is free from interference of antihistamine drugs hydroxyzine and cetirizine

A recent report indicates that hydroxyzine and its active metabolite cetirizine interfere with the particle-enhanced turbidimetric inhibition immunoassay (PENTINA) carbamazepine assay. We studied potential interference of hydroxyzine and cetirizine with the turbidimetric carbamazepine immunoassay on ADVIA 1650 and ADVIA 2400 (Bayer Diagnostics, Tarrytown, NY) analyzers. Aliquots of drug-free serum pools were supplemented with various concentrations of hydroxyzine and cetirizine representing therapeutic, moderate toxic, as well as very toxic concentrations. These samples were assayed by the turbidimetric carbamazepine immunoassay on two analyzers. To study the interference in presence of the analyte, aliquots of a serum pool prepared from patients receiving carbamazepine were further supplemented with various amounts of hydroxyzine and or cetirizine and apparent carbamazepine concentrations were measured again in order to compare with the value of original pool. No apparent carbamazepine concentration was observed when aliquots of drug-free serum were supplemented with hydroxyzine or cetirizine. Moreover, in the carbamazepine pool, the original carbamazepine concentration compared well when aliquots of this serum pool were further supplemented with hydroxyzine or cetirizine. We conclude that the turbidimetric carbamazepine immunoassay is free from interference of hydroxyzine and cetirizine.

Involvement of enzymes other than CYPs in the oxidative metabolism of xenobiotics

Although the majority of oxidative metabolic reactions are mediated by the CYP superfamily of enzymes, non-CYP-mediated oxidative reactions can play an important role in the metabolism of xenobiotics. The (major) oxidative enzymes, other than CYPs, involved in the metabolism of drugs and other xenobiotics are: the flavin-containing monooxygenases, the molybdenum hydroxylases (aldehyde oxidase and xanthine oxidase), the prostaglandin H synthase, the lipoxygenases, the amine oxidases (monoamine, polyamine, diamine and semicarbazide-sensitive amine oxidases) and the alcohol and aldehyde dehydrogenases. In a similar manner to CYPs, these oxidative enzymes can also produce therapeutically active metabolites and reactive/toxic metabolites, modulate the efficacy of therapeutically active drugs or contribute to detoxification. Many of them have been shown to be important in endobiotic metabolism, and, consequently, interactions between drugs and endogenous compounds might occur when they are involved in drug metabolism. In general, most non-CYP oxidative enzymes appear to be noninducible or much less inducible than the CYP system, although some of them may be as inducible as some CYPs. Some of these oxidative enzymes exhibit polymorphic expression, as do some CYPs. It is possible that the contribution of non-CYP oxidative enzymes to the overall metabolism of xenobiotics is underestimated, as most investigations of drug metabolism in discovery and lead optimisation are performed using in vitro test systems optimised for CYP activity.

False-positive Serum Tricyclic Antidepressant Concentrations Using Fluorescence Polarization Immunoassay Due to the Presence of Hydroxyzine and Cetirizine

A recent report indicates that hydroxyzine and its active metabolite cetirizine interfere with the PENTINA carbamazepine assay. The potential interference of hydroxyzine and cetirizine with the fluorescence polarization immunoassay (FPIA) and CEDIA assay of carbamazepine as well as with the fluorescence polarization immunoassay of tricyclic antidepressants (TCA) was studied. Aliquots of drug-free serum pools were supplemented with various concentrations of hydroxyzine and cetirizine representing therapeutic, mild to moderate toxic as well as very toxic concentrations. Then apparent carbamazepine and TCA concentrations were measured by immunoassays. Although no interference of hydroxyzine and cetirizine was observed with carbamazepine assays (FPIA and CEDIA), significant apparent TCA concentrations were observed when aliquots of drug-free serum were supplemented with hydroxyzine or cetirizine. Mathematical formula was devised to predict hydroxyzine and/or cetirizine concentration in serum based on observed apparent TCA levels. Hydroxyzine and cetirizine also falsely increased total TCA values when aliquots of serum pool prepared from patients receiving TCA were further supplemented with these drugs. In conclusion, hydroxyzine and cetirizine do not interfere with the FPIA and CEDIA carbamazepine assays but interfere with the measurement of total TCA using the FPIA.