Pharmacogenetics of CYP3A5 on Carbamazepine pharmacokinetics in epileptic patients developing toxicity

Pharmacogenetics of Carbamazepine and Valproate: Focus on Polymorphisms of Drug Metabolizing Enzymes and Transporters

Pharmacogenomics can identify polymorphisms in genes involved in drug pharmacokinetics and pharmacodynamics determining differences in efficacy and safety and causing inter-individual variability in drug response. Therefore, pharmacogenomics can help clinicians in optimizing therapy based on patient's genotype, also in psychiatric and neurological settings. However, pharmacogenetic screenings for psychotropic drugs are not routinely employed in diagnosis and monitoring of patients treated with mood stabilizers, such as carbamazepine and valproate, because their benefit in clinical practice is still controversial. In this review, we summarize the current knowledge on pharmacogenetic biomarkers of these anticonvulsant drugs.

The effect of cannabidiol on the pharmacokinetics of carbamazepine in rats

Carbamazepine (CBZ) is mainly metabolized by CYP3A4 into carbamazepine-10,11-epoxide (CBZE). Cannabidiol (CBD) is a potent inhibitor of the CYP3A family. The aim of this study is to determine the effect of acute and chronic administration of CBD on the pharmacokinetics of CBZ and CBZE. Male SD rats were assigned into four acute and four chronic groups: control (CBZ only), positive control (ketoconazole), low-dose cannabidiol (l-CBD), and high-dose cannabidiol (h-CBD). Acute CBD groups were administered a single dose of CBD, while chronic CBD groups were given multiple doses of CBD for 14 days (q.d.) before CBZ administration. Plasma samples had been collected and analyzed for CBZ and CBZE, then their noncompartmental pharmacokinetic parameters before and after CBD administration were determined. The co-administration of a single l-CBD has significantly increased CBZ's [Formula: see text] by 53.1%. Furthermore, CBZE kinetics showed a significant decrease in C_max by 31.8%. Acute h-CBD caused similar effects on CBZ's [Formula: see text] with 40.4% significant decrease in CBZE's C_max, when compared to the control. Chronic h-CBD caused a significant decrease in CBZ's C_max and [Formula: see text] by 75.3% and 65.7%, respectively. Besides, [Formula: see text] and C_max of CBZE significantly decreased by 75.3% and 78.3%, respectively. These results demonstrated that the pharmacokinetics of CBZ and CBZE had been significantly affected by CBD. When CBD has been administered as a single dose, the effect is believed to be mainly caused by the inhibition of CBZ metabolism through CYP3A. The effect of chronic administration of CBD probably includes kinetic pathways other than the inhibition of CYP3A-dependent pathways. Graphical abstract.

Pooled bioequivalence study database from Turkey: characterization of adverse events and determination of split points based on Gini Index as a promising method

Background

Manufacturing of and medication with generic drugs is increasing around the world. Bioequivalence (BE) studies are being performed routinely by Contract Research Organisations (CROs) in Turkey. However, an overall evaluation for the attended volunteers, examined Active Pharmaceutical Ingredients (APIs) and the observed adverse events have not been studied in the field.

Objective

Our aim was to revisit and compile the BE studies carried out between the years 2000–2013 of a CRO (N-CRO) in Turkey.

Methods

A dataset of 261 BE studies has been created for the observed adverse events with regards to the frequency, type, and drug subgroups. As an advanced evaluation, the Gini Index method has been used in the 63 available BE studies to obtain split points for two pharmacokinetic parameters, area under the plasma/serum concentration (AUC) and maximum plasma/serum concentration (Cmax), in order to investigate their likely effect on the adverse events.

Results

Thousand six hundred and forty two adverse events were found in the 261 BE studies involving 7828 volunteers with the frequency of 6.29 per study and 0.21 per volunteer. The most frequently observed adverse events were; headache, somnolence, nausea, dizziness and vomiting, respectively. Hundred and nine different APIs were observed. ‘Genitourinary system and sex hormones’ subgroup drugs had the highest frequency of the adverse events. Adverse event frequencies above the identified split points for Cmax and AUC values were higher than the frequencies below them.

Conclusion

The review of 13 years period of BE studies revealed that the demographic properties of the volunteers and the study designs were in compliance with national and international guidelines. The promising outcome could be showing the increase of the adverse event frequencies above the obtained split points as the reflection of the likely individual pharmacokinetic differences in the adverse event occurence.

Electronic supplementary material

The online version of this article (doi:10.1186/s40064-016-2527-4) contains supplementary material, which is available to authorized users.