Characterization of the time course of carbamazepine deinduction by an enzyme turnover model

The use of therapeutic drug monitoring to highlight an over-looked drug-drug interaction leading to imatinib treatment failure

BACKGROUND

Chronic oral anticancer therapies, are increasingly prescribed and present new challenges including the enhanced risk of overlooked drug-drug interactions (DDIs). Lengthy treatments and patients' management by different professionals can lead to serious prescribing errors that therapeutic drug monitoring (TDM) can help identifying thus allowing a more effective and safer treatment of patients with polypharmacy.

OBJECTIVES

This report aims to exemplify how an intensified pharmacological approach could help in the clinical monitoring of patients on chronic treatments.

METHODS

A patient with gastrointestinal stromal tumor was referred to our clinical pharmacology service due to tumor progression while on imatinib therapy. The investigation was based on TDM, pharmacogenetics, DDI evaluation and Circulating tumor DNA (ctDNA) analysis. The patient underwent repeated blood samplings to measure imatinib and norimatinib plasma concentrations through a validated LC-MS/MS method. Polymorphisms affecting genes involved in imatinib metabolism and transport were investigated using SNPline PCR Genotyping System. Drug-drug interactions were evaluated though Lexicomp. ctDNA analysis was performed on MiSeq platform.

RESULTS

TDM analysis revealed that the patient was underexposed to imatinib (Cmin = 406 ng/mL; target Cmin = 1100 ng/mL). Subsequent DDI analysis highlighted a dangerous interaction with carbamazepine, via CYP3A4 and P-gp strong induction, omitted at the time of imatinib treatment start. No relevant pharmacogenetic variants were identified and appropriate compliance to treatment was ascertained. ctDNA monitoring was performed to assess potential tumor-related resistance to imatinib. Carbamazepine was cautiously switched to a non-interacting antiepileptic drug, restoting IMA plasma concentration (i.e. Cmin = 4298 ng/mL). The progression of the disease, which in turn led to the patient's death, was also witnessed by an increasing fraction of ctDNA in plasma.

CONCLUSION

The active pharmacological monitoring allowed the identification of a dangerous previously over-looked DDI leading to IMA under-exposure. The switch to a different antiepileptic treatment, reversed the effect of DDI, restoring therapeutic IMA plasmatic concentrations.

Analysis of Time-Dependent Pharmacokinetics Using In Vitro-In Vivo Extrapolation and Physiologically Based Pharmacokinetic Modeling

SCR430, a sorafenib derivative, is an investigational drug exhibiting anti-tumor action. This study aimed to have a mechanistic understanding of SCR430's time-dependent pharmacokinetics (TDPK) through an ex vivo study combined with an in vitro-in vivo extrapolation (IVIVE) and physiologically based pharmacokinetic (PBPK) modeling. A non-compartmental pharmacokinetic analysis was performed after intravenous SCR430 administration in female Sprague-Dawley rats for a control group (no treatment), a vehicle group (vehicle only, 14 days, PO), and a repeated-dosing group (SCR430, 30 mg/kg/day, 14 days, PO). In addition, hepatic uptake and metabolism modulation were investigated using isolated hepatocytes from each group of rats. The minimal PBPK model based on IVIVE was constructed to explain SCR430's TDPK. Repeated SCR430 administration decreased the systemic exposure by 4.4-fold, which was explained by increased hepatic clearance (4.7-fold). The ex vivo study using isolated hepatocytes from each group suggested that the increased hepatic uptake (9.4-fold), not the metabolic activity, contributes to the increased hepatic clearance. The minimal PBPK modeling based on an ex vivo study could explain the decreased plasma levels after the repeated doses. The current study demonstrates the TDPK after repeated dosing by hepatic uptake induction, not hepatic metabolism, as well as the effectiveness of an ex vivo approach combined with IVIVE and PBPK modeling to investigate the TDPK.

Using nirmatrelvir/ritonavir in patients with epilepsy: an update from the Israeli ILAE Chapter

Presented herein are recommendations for use of nirmatrelvir/ritonavir in patients with epilepsy, as issued by the Steering Committee of the Israeli chapter of the International League Against Epilepsy. The recommendations suggest that patients on moderate‐to‐strong enzyme‐inducing antiseizure medications (ASMs) and everolimus should not be treated with nirmatrelvir/ritonavir; rectal diazepam may be used as an alternative to buccal midazolam; doses of ASMs that are cytochrome P450 (CYP3A4) substrates might be adjusted; and patients treated with combinations of nirmatrelvir/ritonavir and ASMs that are CYP3A4 substrates or lamotrigine should be monitored for drug efficacy and adverse drug reactions.

Novel treatments for chronic pain: moving beyond opioids

It is essential that safe and effective treatment options be available to patients suffering from chronic pain. The emergence of an opioid epidemic has shaped public opinions and created stigmas surrounding the use of opioids for the management of pain. This reality, coupled with high risk of adverse effects from chronic opioid use, has led chronic pain patients and their healthcare providers to utilize nonopioid treatment approaches. In this review, we will explore a number of cellular reorganizations that are associated with the development and progression of chronic pain. We will also discuss the safety and efficacy of opioid and nonopioid treatment options for chronic pain. Finally, we will review the evidence for adenylyl cyclase type 1 (AC1) as a novel target for the treatment of chronic pain.

Evaluation of drug-drug interactions in hospitalized patients on medications for OUD

Introduction

Medications used to treat OUD have common metabolic pathways and pharmacodynamic properties that can lead to drug-drug interactions (DDIs) that may go unnoticed in the inpatient setting. The purpose of this study was to identify the frequency of DDIs between medications prescribed for OUD and commonly used inpatient medications.

Methods

This was a retrospective review of orders for buprenorphine, buprenorphine-naloxone, and methadone to identify potential DDIs. Adult inpatients with an order for one of these medications for OUD were included. Medication regimens were evaluated throughout the inpatient stay and on day of discharge for DDIs. DDIs were classified by severity and type of interaction (increased risk of QT prolongation, additive CNS effects/respiratory depression, and opioid withdrawal). The primary endpoint was the number of potential DDIs. Other endpoints included number of each classification/severity of DDI, duration of therapy of interacting medications, and modifications made to OUD medications because of DDIs.

Results

A total of 102 patients were included, with 215 inpatient interactions and 83 interactions at discharge identified. While inpatient, 85% of patients were on an interacting medication, and 46% of patients were on an interacting medication at discharge. The most common classification of DDI was additive CNS effects/respiratory depression (68.8% inpatient, 50.6% discharge), followed by QT prolongation (24.2% inpatient, 45.8% discharge). The majority of DDIs were classified as requiring close monitoring rather than contraindicated.

Discussion

There are opportunities to optimize the prescribing practices surrounding OUD medications in both the inpatient setting and at discharge to ensure patient safety.

Deinduction of P-glycoprotein resulting in delayed viral response during hepatitis C treatment

WHAT IS KNOWN AND OBJECTIVE

Drug-drug interactions can involve inhibition or induction of cell membrane transporters. Deinduction occurs after an inducing agent is stopped.

CASE SUMMARY

This case describes suspected P-glycoprotein (P-gp) deinduction by carbamazepine resulting in a slow viral response during treatment of chronic hepatitis C virus (HCV) infection. Evidence of deinduction occurred beyond clearance of carbamazepine and resulted in extension of HCV treatment.

WHAT IS NEW

The understanding of the role P-gp transport plays in drug elimination is relatively new and evidence of P-gp deinduction is variable.

CONCLUSION

Clinicians should consider deinduction when starting and stopping medications involving strong inducers of P-gp transport proteins.

Drug withdrawal in the epilepsy monitoring unit - The patsalos table

Investigation of possible candidates for epilepsy surgery will usually require inpatient EEG to capture seizures and allow full operative planning. Withdrawal of antiepileptic drugs increases the yield of this valuable diagnostic information and the benefits of this should justify any increase in the risk of harm associated with these seizures This paper outlines our opinion on what would constitute proposed best practice for management of antiepileptic drug (AED) dosing when patients are admitted for monitoring of seizures to an epilepsy monitoring unit (EMU). In the vast majority of cases EMU admissions are safe and, even if seizures occur, will pass off without complication. Previous guidance has concentrated on ensuring practice around technical aspects of EEG monitoring itself and staffing within the unit. In this guidance we aim to outline optimally safe ways of ensuring that EMUs ensure the minimisation of risk to the patients admitted under their care. We propose an algorithm for enhancing the safety of AED withdrawal in VT admissions while ensuring adequate seizure yields. Risk minimisation requires planned management of drug dosing (with reduction if appropriate), provision of adequate rescue medication, and adequate supervision to allow rapid response to generalised seizures. This algorithm is accompanied by a table which uses knowledge of the clinical and pharmacological properties of each AED to ensure dose withdrawal and reduction is timely and safe taking into account the severity and frequency of the individual's seizures.

Derivation of CYP3A4 and CYP2B6 degradation rate constants in primary human hepatocytes: A siRNA-silencing-based approach

The first-order degradation rate constant (k_deg) of cytochrome P450 (CYP) enzymes is a known source of uncertainty in the prediction of time-dependent drug-drug interactions (DDIs) in physiologically-based pharmacokinetic (PBPK) modelling. This study aimed to measure CYP k_deg using siRNA to suppress CYP expression in primary human hepatocytes followed by incubation over a time-course and tracking of protein expression and activity to observe degradation. The magnitude of gene knockdown was determined by qPCR and activity was measured by probe substrate metabolite formation and CYP2B6-Glo™ assay. Protein disappearance was determined by Western blotting. During a time-course of 96 and 60 h of incubation, over 60% and 76% mRNA knockdown was observed for CYP3A4 and CYP2B6, respectively. The k_deg of CYP3A4 and CYP2B6 protein was 0.0138 h^-1 (±0.0023) and 0.0375 h^-1 (±0.025), respectively. The k_deg derived from probe substrate metabolism activity was 0.0171 h^-1 (±0.0025) for CYP3A4 and 0.0258 h^-1 (±0.0093) for CYP2B6. The CYP3A4 k_deg values derived from protein disappearance and metabolic activity were in relatively good agreement with each other and similar to published values. This novel approach can now be used for other less well-characterised CYPs.

Sodium Channel Blockers in the Treatment of Epilepsy

Sodium channel blockers have been the mainstay of the pharmacological management of focal and generalised tonic-clonic seizures for more than 70 years. The focus of this paper will be on phenytoin, carbamazepine, lamotrigine, oxcarbazepine, rufinamide, lacosamide and eslicarbazepine acetate. All these antiepileptic drugs have similar efficacy and share similar dose-dependent, adverse effect profiles, although phenytoin, carbamazepine and oxcarbazepine are more likely to cause idiosyncratic reactions than the others. With the exception of lamotrigine, rufinamide and lacosamide, all are enzyme inducers and most are minor teratogens; although data on teratogenicity are sparse with lacosamide and eslicarbazepine acetate. There is increasing evidence that these drugs differ mechanistically, with the newer agents, lacosamide and eslicarbazepine acetate, having their major pharmacological effect on the slow inactivation state of the sodium channel, which may be associated with better tolerability at higher dosage, although hard evidence in support of this observation is currently not available. Rufinamide is licensed only for Lennox-Gastaut syndrome in children aged 4 years and above. There is a move away from using enzyme inducers, particularly phenytoin and carbamazepine, in everyday clinical practice. There seems little doubt, however, that some sodium channel blockers will have an enduring place in the management of epilepsy well into the 21st century.

Pharmacokinetic Drug-Drug Interactions of Mood Stabilizers and Risperidone in Patients Under Combined Treatment

BACKGROUND

The combination of anticonvulsant mood stabilizers with antipsychotic drugs may lead to clinically relevant drug-drug interactions. The objective of the study was to identify pharmacokinetic interactions of different mood stabilizers on the metabolism of risperidone (RIS) under natural conditions.

METHODS

A large therapeutic drug monitoring database containing plasma concentrations of RIS and its metabolite 9-hydroxy-RIS (9-OH-RIS) of 1,584 adult patients was analyzed. Four groups (n = 1,072) were compared: a control group without a potentially cytochrome interacting comedication (R0, n = 852), a group comedicated with valproate (VPA) (RVPA, n = 153), a group comedicated with lamotrigine (LMT) (RLMT, n = 46), and a group under concomitant medication with carbamazepine (CBZ) (RCBZ, n = 21). Dose-adjusted plasma concentrations (C/D ratio) for RIS, 9-OH-RIS and active moiety (AM) (RIS + 9-OH-RIS), as well as metabolic ratios (RIS/9-OH-RIS) were computed.

RESULTS

Groups did not differ with regard to the daily dosage (P = 0.46). Differences were detected for the distributions of the C/D ratios for RIS, 9-OH-RIS and AM (P = 0.003, P < 0.001 and P < 0.001, respectively). Differences remained significant after conducting a Bonferroni correction (P = 0.0125). Pairwise comparisons of the concomitant medication groups with the control group revealed significant differences; RIS C/D ratios were significantly higher in the VPA and the LMT group than in the control group (P = 0.013; P = 0.021). However, these differences did not remain significant after Bonferroni correction. In contrast, CBZ-treated patients showed lower dose-adjusted plasma concentrations of 9-OH-RIS (P < 0.001) as well as the AM (P < 0.001) than the control group; this difference survived the Bonferroni correction.

CONCLUSIONS

The data give evidence for pharmacokinetic interactions between RIS and different anticonvulsant mood stabilizers. Carbamazepine decreased serum concentrations of 9-OH-RIS and the AM when compared with the control group. In case of VPA and LMT, findings were less significant; hints for a weak RIS metabolism inhibition by LMT of unclear clinical significance were found.

Changes in hormone and lipid levels in male patients with focal seizures when switched from carbamazepine to lacosamide as adjunctive treatment to levetiracetam: A small phase IIIb, prospective, multicenter, open-label trial

Treatment with enzyme-inducing antiepileptic drugs (AEDs) such as carbamazepine (CBZ) can lead to changes in reproductive, endocrine, and lipid parameters, resulting in clinical symptoms for some patients. Previous studies indicate that these changes can be reversed by switching to a nonenzyme-inducing AED. Lacosamide is a newer-generation AED, not known to induce or strongly inhibit cytochrome P450 (CYP450) enzymes. In this phase IIIb, prospective, multicenter, open-label, single-arm trial (NCT01375374), the serum concentrations of CYP-related reproductive hormones, thyroid hormones, and lipids were assessed in otherwise healthy male patients with focal seizures (N=11), before and after a switch from CBZ (600-1200mg/day at baseline) to lacosamide (target dose: 400mg/day by the end of titration) as adjunctive treatment to the nonenzyme-inducing AED levetiracetam (LEV, stable dosage of >1000mg/day throughout). Cross titration took place over 4weeks, followed by an 8-week maintenance period. Serum measurements were conducted at baseline and at the end of maintenance. The median serum sex-hormone-binding globulin (SHBG) concentration was towards the higher end of the normal range at baseline and decreased following the switch (61.7 to 47.5nmol/L, N=10, p=0.027 by Wilcoxon signed-rank test). Free androgen index (100×testosterone/SHBG) and free thyroxine serum concentration increased (25.4 to 36.4 and 13.0 to 14.9pmol/L, respectively, both N=10 and p=0.002). At baseline, the median progesterone serum concentration was below the normal range (0.7nmol/L), whereas median cholesterol and low-density lipoprotein concentrations were above the normal range (5.5 and 3.6mmol/L, respectively). By the end of maintenance, all measured parameters were within the normal range. The safety and tolerability profile of lacosamide was consistent with that observed in previous studies. Furthermore, antiseizure efficacy appeared to be maintained, suggesting that deinduction of CYP enzymes following a switch from CBZ to lacosamide as adjunctive therapy to LEV is feasible within 8weeks and is associated with normalization of serum parameters.

Carbamazepine

This chapter includes the aspects of carbamazepine. The drug is synthesized by the use of 5H-dibenz[b,f]azepine and phosgene followed by subsequent reaction with ammonia. Carbamazepine is generally used for the treatment of seizure disorders and neuropathic pain, it is also important as off-label for a second-line treatment for bipolar disorder and in combination with an antipsychotic in some cases of schizophrenia when treatment with a conventional antipsychotic alone has failed. Other uses may include attention deficit hyperactivity disorder, schizophrenia, phantom limb syndrome, complex regional pain syndrome, borderline personality disorder, and posttraumatic stress disorder. The chapter discusses the drug metabolism and pharmacokinetics and presents various methods of analysis of this drug such electrochemical analysis, spectroscopic analysis, and chromatographic techniques of separation. It also discusses its physical properties such as solubility characteristics, X-ray powder diffraction pattern, and thermal methods of analysis. The chapter is concluded with a discussion on its biological properties such as activity, toxicity, and safety.

Safety of an intravenous formulation of lamotrigine

PURPOSE

Intravenous (IV) formulations are useful when treating patients where oral administration is not possible and to study certain pharmacokinetic parameters such as bioavailability. We developed a stable-labeled IV formulation of lamotrigine (LTG) for studying pharmacokinetics in epilepsy patients.

METHODS

Stable-labeled IV LTG was given to 20 persons with epilepsy (6 men; 14 women) with a mean age of 34.8 years (SD 11.7). A 50mg dose of LTG (stable labeled) was given intravenously and replaced 50mg of the regular morning oral dose of LTG (unlabeled, commercially available formulation).

RESULTS

No significant changes in blood pressure, heart rate, or adverse events including rash were attributed to administration of a 50-mg dose of the intravenous LTG formulation.

CONCLUSION

Our results show that LTG base that is complexed with 2-hydroxypropyl-β-cyclodextrin and stable-labeled can be given safely as a tracer replacement dose.

Population pharmacokinetics of carbamazepine in elderly patients

BACKGROUND

Carbamazepine is a commonly used antiepileptic drug in elderly patients. This study analyzed prospective data collected as part of a randomized, double-blinded trial of newly diagnosed epilepsy patients. The aims of this study were to determine the pharmacokinetic parameters and their variability of carbamazepine in elderly patients and to quantify the effect of covariates on these parameters.

METHODS

Prospectively collected carbamazepine concentrations from 121 patients aged 60 years or older were used to develop a population pharmacokinetic model. Data were analyzed by a nonlinear mixed effects model (NONMEM). A 1-compartment model with first-order absorption and elimination was used to characterize the time course of carbamazepine concentration. Model evaluation and the predictive performance of the final model were assessed using the nonparametric bootstrap approach.

RESULTS

The apparent clearance (CL/F) of carbamazepine in this community-dwelling elderly population was estimated to be 3.59 L/h with an interindividual variability of 18.1%. The CL/F increases 23% in patients comedicated with phenytoin. The volume of distribution (V/F) was estimated to be 102 L with an interindividual variability of 74.7%.

CONCLUSIONS

Carbamazepine clearance was not associated with body weight or any parameterization of body size nor was age or race or any marker of hepatic or renal function in community dwelling elderly patients. Elderly patients on concurrent phenytoin therapy may require a smaller 23% higher dose on average, about half that reported for younger patients.