Population pharmacokinetic model and limited sampling strategy for clozapine using plasma and dried blood spot samples

BACKGROUND: To improve efficacy, therapeutic drug monitoring is often used in clozapine therapy. Trough level monitoring is regular, but trough levels provide limited information about the pharmacokinetics of clozapine and exposure in time. The area under the concentration time curve (AUC) is generally valued as better marker of drug exposure in time but calculating AUC needs multiple sampling. An alternative approach is a limited sampling scheme in combination with a population pharmacokinetic model meant for Bayesian forecasting. Furthermore, multiple venepunctions can be a burden for the patient, whereas collecting samples by means of dried blood spot (DBS) sampling can facilitate AUC-monitoring, making it more patient friendly. OBJECTIVE: Development of a population pharmacokinetic model and limited sampling strategy for estimating AUC(0-12h) (a twice-daily dosage regimen) and AUC(0-24h) (a once-daily dosage regimen) of clozapine, using a combination of results from venepunctions and DBS sampling. METHOD: From 15 schizophrenia patients, plasma and DBS samples were obtained before administration and 2, 4, 6, and 8 h after clozapine intake. MwPharm(®) pharmacokinetic software was used to parameterize a population pharmacokinetic model and calculate limited sampling schemes. RESULTS: A three-point sampling strategy with samples at 2, 6, and 8 h after clozapine intake gave the best estimation of the clozapine AUC(0-12h) and at 4, 10, and 11 h for the AUC(0-24h). For clinical practice, however, a two-point sampling strategy with sampling points at 2 and 6 h was sufficient to estimate AUC(0-12h) and at 4 and 11 h for AUC(0-24h). CONCLUSION: A pharmacokinetic model with a two–time point limited sampling strategy meant for Bayesian forecasting using DBS sampling gives a better prediction of the clozapine exposure in time, expressed as AUC, compared to trough level monitoring. This limited sampling strategy might therefore provide a more accurate prediction of effectiveness and occurrence of side effects compared to trough level monitoring. The use of DBS samples also makes the collection of clozapine samples easier and wider applicable

Dried blood spot analysis for therapeutic drug monitoring of Clozapine

Background: Schizophrenia is a psychiatric disorder that affects approximately 0.4%–1% of the population worldwide. Diagnosis of schizophrenia is based primarily on Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria. Clozapine is an antipsychotic drug that is mainly used in the treatment of schizophrenia patients who are refractory or intolerant to at least 2 other antipsychotics. Due to the high variability in pharmacokinetics of clozapine, therapeutic drug monitoring (TDM) is highly recommended for clozapine therapy. Objective: To develop and clinically validate a novel sampling method using dried blood spot (DBS) to support TDM of clozapine and norclozapine. Methods: From June 2014 to September 2014, 15 schizophrenia patients (18–55 years) treated with clozapine were included. Plasma, DBS samples made from venous samples (VDBS), and finger prick DBS (DBS) samples were obtained before administration and 2, 4, 6, and 8 hours after clozapine intake. The study was repeated in 6 Russian patients for external validation. Passing-Bablok regression and Bland-Altman analysis were used to compare the DBS, VDBS, and plasma results for clozapine and norclozapine. Results: The DBS validation results showed good linearity over the concentration time curve measured for clozapine and norclozapine. The accuracy and between- and within-day precision variation values were within accepted ranges. Different blood spot volumes and hematocrit values had no significant influence on the results. The DBS samples were stable at 20°C and 37°C for 2 weeks and at −20°C for 2 years. The mean clozapine and norclozapine DBS/plasma ratios were, respectively, 0.80 (95% CI, 0.76 to 0.85) and 1.063 (95% CI, 1.027 to 1.099) in Dutch patients. The mean clozapine DBS/DPS ratio in Russian patients was 0.70 (95% CI, 0.64 to 0.76). Conclusion: DBS analysis is a reliable tool for blood sampling and performing TDM of clozapine and norclozapine in daily practice and substantially extends the opportunities for TDM of clozapine

Decreased Histone Acetylation Levels at Th1 and Regulatory Loci after Induction of Food Allergy

Immunoglobulin E (IgE)-mediated allergy against cow's milk protein fractions such as whey is one of the most common food-related allergic disorders of early childhood. Histone acetylation is an important epigenetic mechanism, shown to be involved in the pathogenesis of allergies. However, its role in food allergy remains unknown. IgE-mediated cow's milk allergy was successfully induced in a mouse model, as demonstrated by acute allergic symptoms, whey-specific IgE in serum, and the activation of mast cells upon a challenge with whey protein. The elicited allergic response coincided with reduced percentages of regulatory T (Treg) and T helper 17 (Th17) cells, matching decreased levels of H3 and/or H4 histone acetylation at pivotal Treg and Th17 loci, an epigenetic status favoring lower gene expression. In addition, histone acetylation levels at the crucial T helper 1 (Th1) loci were decreased, most probably preceding the expected reduction in Th1 cells after inducing an allergic response. No changes were observed for T helper 2 cells. However, increased histone acetylation levels, promoting gene expression, were observed at the signal transducer and activator of transcription 6 (Stat6) gene, a proallergic B cell locus, which was in line with the presence of whey-specific IgE. In conclusion, the observed histone acetylation changes are pathobiologically in line with the successful induction of cow's milk allergy, to which they might have also contributed mechanistically

Decreased Histone Acetylation Levels at Th1 and Regulatory Loci after Induction of Food Allergy

Immunoglobulin E (IgE)-mediated allergy against cow's milk protein fractions such as whey is one of the most common food-related allergic disorders of early childhood. Histone acetylation is an important epigenetic mechanism, shown to be involved in the pathogenesis of allergies. However, its role in food allergy remains unknown. IgE-mediated cow's milk allergy was successfully induced in a mouse model, as demonstrated by acute allergic symptoms, whey-specific IgE in serum, and the activation of mast cells upon a challenge with whey protein. The elicited allergic response coincided with reduced percentages of regulatory T (Treg) and T helper 17 (Th17) cells, matching decreased levels of H3 and/or H4 histone acetylation at pivotal Treg and Th17 loci, an epigenetic status favoring lower gene expression. In addition, histone acetylation levels at the crucial T helper 1 (Th1) loci were decreased, most probably preceding the expected reduction in Th1 cells after inducing an allergic response. No changes were observed for T helper 2 cells. However, increased histone acetylation levels, promoting gene expression, were observed at the signal transducer and activator of transcription 6 (Stat6) gene, a proallergic B cell locus, which was in line with the presence of whey-specific IgE. In conclusion, the observed histone acetylation changes are pathobiologically in line with the successful induction of cow's milk allergy, to which they might have also contributed mechanistically