An in vitro approach to estimate putative inhibition of buprenorphine and norbuprenorphine glucuronidation

Evidence-based strategies for the characterisation of human drug and chemical glucuronidation in vitro and UDP-glucuronosyltransferase reaction phenotyping

Enzymes of the UDP-glucuronosyltransferase (UGT) superfamily contribute to the elimination of drugs from almost all therapeutic classes. Awareness of the importance of glucuronidation as a drug clearance mechanism along with increased knowledge of the enzymology of drug and chemical metabolism has stimulated interest in the development and application of approaches for the characterisation of human drug glucuronidation in vitro, in particular reaction phenotyping (the fractional contribution of the individual UGT enzymes responsible for the glucuronidation of a given drug), assessment of metabolic stability, and UGT enzyme inhibition by drugs and other xenobiotics. In turn, this has permitted the implementation of in vitro - in vivo extrapolation approaches for the prediction of drug metabolic clearance, intestinal availability, and drug-drug interaction liability, all of which are of considerable importance in pre-clinical drug development. Indeed, regulatory agencies (FDA and EMA) require UGT reaction phenotyping for new chemical entities if glucuronidation accounts for ≥25% of total metabolism. In vitro studies are most commonly performed with recombinant UGT enzymes and human liver microsomes (HLM) as the enzyme sources. Despite the widespread use of in vitro approaches for the characterisation of drug and chemical glucuronidation by HLM and recombinant enzymes, evidence-based guidelines relating to experimental approaches are lacking. Here we present evidence-based strategies for the characterisation of drug and chemical glucuronidation in vitro, and for UGT reaction phenotyping. We anticipate that the strategies will inform practice, encourage development of standardised experimental procedures where feasible, and guide ongoing research in the field.

Physiologically-Based Pharmacokinetic (PBPK) Modeling of Buprenorphine in Adults, Children and Preterm Neonates

Buprenorphine plays a crucial role in the therapeutic management of pain in adults, adolescents and pediatric subpopulations. However, only few pharmacokinetic studies of buprenorphine in children, particularly neonates, are available as conducting clinical trials in this population is especially challenging. Physiologically-based pharmacokinetic (PBPK) modeling allows the prediction of drug exposure in pediatrics based on age-related physiological differences. The aim of this study was to predict the pharmacokinetics of buprenorphine in pediatrics with PBPK modeling. Moreover, the drug-drug interaction (DDI) potential of buprenorphine with CYP3A4 and P-glycoprotein perpetrator drugs should be elucidated. A PBPK model of buprenorphine and norbuprenorphine in adults has been developed and scaled to children and preterm neonates, accounting for age-related changes. One-hundred-percent of the predicted AUC_last values in adults (geometric mean fold error (GMFE): 1.22), 90% of individual AUC_last predictions in children (GMFE: 1.54) and 75% in preterm neonates (GMFE: 1.57) met the 2-fold acceptance criterion. Moreover, the adult model was used to simulate DDI scenarios with clarithromycin, itraconazole and rifampicin. We demonstrate the applicability of scaling adult PBPK models to pediatrics for the prediction of individual plasma profiles. The novel PBPK models could be helpful to further investigate buprenorphine pharmacokinetics in various populations, particularly pediatric subgroups.

Gestational changes in buprenorphine exposure: A physiologically-based pharmacokinetic analysis

AIMS

Buprenorphine (BUP) is approved by the US Food and Drug Administration for the treatment of opioid addiction. The current dosing regimen of BUP in pregnant women is based on recommendations designed for nonpregnant adults. However, physiological changes during pregnancy may alter BUP exposure and efficacy. The objectives of this study were to develop a physiologically-based pharmacokinetic (PBPK) model for BUP in pregnant women, to predict changes in BUP exposure at different stages of pregnancy, and to demonstrate the utility of PBPK modelling in optimizing BUP pharmacotherapy during pregnancy.

METHODS

A full PBPK model for BUP was initially built and validated in healthy subjects. A fetoplacental compartment was included as a combined compartment in this model to simulate pregnancy induced anatomical and physiological changes. Further, gestational changes in physiological parameters were incorporated in this model. The PBPK model predictions of BUP exposure in pregnancy and during the postpartum period were compared to published data from a prospective clinical study.

RESULTS

The predicted BUP plasma concentration-time profiles in the virtual pregnant populations are consistent with the observed data in the 2nd and 3rd trimesters, and the postpartum period. The differences in the predicted means of dose normalized area under the plasma drug concentration-time curve up to 12 h, average concentration and maximum concentration were within ±25% of the corresponding observed means with the exception of average concentration in the 3rd trimester (-26.3%).

CONCLUSION

PBPK model-based simulation may be a useful tool to optimize BUP pharmacotherapy during pregnancy, obviating the need to perform pharmacokinetic studies in each trimester and the postpartum period that normally require intensive blood sampling.

A physiologically based pharmacokinetic modelling approach to predict buprenorphine pharmacokinetics following intravenous and sublingual administration

AIMS

Opioid dependence is associated with high morbidity and mortality. Buprenorphine (BUP) is approved by the Food and Drug Administration to treat opioid dependence. There is a lack of clear consensus on the appropriate dosing of BUP due to interpatient physiological differences in absorption/disposition, subjective response assessment and other patient comorbidities. The objective of the present study was to build and validate robust physiologically based pharmacokinetic (PBPK) models for intravenous (IV) and sublingual (SL) BUP as a first step to optimizing BUP pharmacotherapy.

METHODS

BUP-PBPK modelling and simulations were performed using SimCyp® by incorporating the physiochemical properties of BUP, establishing intersystem extrapolation factors-based in vitro-in-vivo extrapolation (IVIVE) methods to extrapolate in vitro enzyme activity data, and using tissue-specific plasma partition coefficient estimations. Published data on IV and SL-BUP in opioid-dependent and non-opioid-dependent patients were used to build the models. Fourteen model-naïve BUP-PK datasets were used for inter- and intrastudy validations.

RESULTS

The IV and SL-BUP-PBPK models developed were robust in predicting the multicompartment disposition of BUP over a dosing range of 0.3-32 mg. Predicted plasma concentration-time profiles in virtual patients were consistent with reported data across five single-dose IV, five single-dose SL and four multiple dose SL studies. All PK parameter predictions were within 75-137% of the corresponding observed data. The model developed predicted the brain exposure of BUP to be about four times higher than that of BUP in plasma.

CONCLUSION

The validated PBPK models will be used in future studies to predict BUP plasma and brain concentrations based on the varying demographic, physiological and pathological characteristics of patients.

Effects of mitragynine and 7-hydroxymitragynine (the alkaloids of Mitragyna speciosa Korth) on 4-methylumbelliferone glucuronidation in rat and human liver microsomes and recombinant human uridine 5'-diphospho-glucuronosyltransferase isoforms

Background:

Glucuronidation catalyzed by uridine 5’- diphospho-glucuronosyltransferase (UGT) is a major phase II drug metabolism reaction which facilitates drug elimination. Inhibition of UGT activity can cause drug-drug interaction. Therefore, it is important to determine the inhibitory potentials of drugs on glucuronidation.

Objective:

The objective was to evaluate the inhibitory potentials of mitragynine, 7-hydroxymitragynine, ketamine and buprenorphine, respectively on 4-methylumbelliferone (4-MU) glucuronidation in rat liver microsomes, human liver microsomes and recombinant human UGT1A1 and UGT2B7 isoforms.

Materials and Methods:

The effects of the above four compounds on the formation of 4-MU glucuronide from 4-MU by rat liver microsomes, human liver microsomes, recombinant human UGT1A1 and UGT2B7 isoforms were determined using high-performance liquid chromatography with ultraviolet detection.

Results:

For rat liver microsomes, ketamine strongly inhibited 4-MU glucuronidation with an IC₅₀ value of 6.21 ± 1.51 μM followed by buprenorphine with an IC₅₀ value of 73.22 ± 1.63 μM. For human liver microsomes, buprenorphine strongly inhibited 4-MU glucuronidation with an IC₅₀ value of 6.32 ± 1.39 μM. For human UGT1A1 isoform, 7-hydroxymitragynine strongly inhibited 4-MU glucuronidation with an IC₅₀ value of 7.13 ± 1.16 μM. For human UGT2B7 isoform, buprenorphine strongly inhibited 4-MU glucuronidation followed by 7-hydroxymitragynine and ketamine with respective IC₅₀ values of 5.14 ± 1.30, 26.44 ± 1.31, and 27.28 ± 1.18 μM.

Conclusions:

These data indicate the possibility of drug-drug interaction if 7-hydroxymitragynine, ketamine, and buprenorphine are co-administered with drugs that are UGT2B7 substrates since these three compounds showed significant inhibition on UGT2B7 activity. In addition, if 7-hydroxymitragynine is to be taken with other drugs that are highly metabolized by UGT1A1, there is a possibility of drug-drug interaction to occur.

Reaction phenotyping: advances in the experimental strategies used to characterize the contribution of drug-metabolizing enzymes

During the process of drug discovery, the pharmaceutical industry is faced with numerous challenges. One challenge is the successful prediction of the major routes of human clearance of new medications. For compounds cleared by metabolism, accurate predictions help provide an early risk assessment of their potential to exhibit significant interpatient differences in pharmacokinetics via routes of metabolism catalyzed by functionally polymorphic enzymes and/or clinically significant metabolic drug-drug interactions. This review details the most recent and emerging in vitro strategies used by drug metabolism and pharmacokinetic scientists to better determine rates and routes of metabolic clearance and how to translate these parameters to estimate the amount these routes contribute to overall clearance, commonly referred to as fraction metabolized. The enzymes covered in this review include cytochrome P450s together with other enzymatic pathways whose involvement in metabolic clearance has become increasingly important as efforts to mitigate cytochrome P450 clearance are successful. Advances in the prediction of the fraction metabolized include newly developed methods to differentiate CYP3A4 from the polymorphic enzyme CYP3A5, scaling tools for UDP-glucuronosyltranferase, and estimation of fraction metabolized for substrates of aldehyde oxidase.