Pharmacokinetic simulations of topiramate plasma concentrations following dosing irregularities with extended-release vs. immediate-release formulations

How Missed Doses of Antibiotics Affect Bacteria Growth Dynamics

What should you do if you miss a dose of antibiotics? Despite the prevalence of missed antibiotic doses, there is vague or little guidance on what to do when a dose is forgotten. In this paper, we consider the effects of different patient responses after missing a dose using a mathematical model that links antibiotic concentration with bacteria dynamics. We show using simulations that, in some circumstances, (a) missing just a few doses can cause treatment failure, and (b) this failure can be remedied by simply taking a double dose after a missed dose. We then develop an approximate model that is analytically tractable and use it to understand when it might be advisable to take a double dose after a missed dose.

How drug onset rate and duration of action affect drug forgiveness

Medication nonadherence is one of the largest problems in healthcare today, particularly for patients undergoing long-term pharmacotherapy. To combat nonadherence, it is often recommended to prescribe so-called "forgiving" drugs, which maintain their effect despite lapses in patient adherence. Nevertheless, drug forgiveness is difficult to quantify and compare between different drugs. In this paper, we construct and analyze a stochastic pharmacokinetic/pharmacodynamic (PK/PD) model to quantify and understand drug forgiveness. The model parameterizes a medication merely by an effective rate of onset of effect when the medication is taken (on-rate) and an effective rate of loss of effect when a dose is missed (off-rate). Patient dosing is modeled by a stochastic process that allows for correlations in missed doses. We analyze this "on/off" model and derive explicit formulas that show how treatment efficacy depends on drug parameters and patient adherence. As a case study, we compare the effects of nonadherence on the efficacy of various antihypertensive medications. Our analysis shows how different drugs can have identical efficacies under perfect adherence, but vastly different efficacies for adherence patterns typical of actual patients. We further demonstrate that complex PK/PD models can indeed be parameterized in terms of effective on-rates and off-rates. Finally, we have created an online app to allow pharmacometricians to explore the implications of our model and analysis.

Managing delayed or missed pregabalin doses in patients with focal epilepsy: a Monte Carlo simulation study

BACKGROUND

Delayed or missed doses are inevitable in epilepsy pharmacotherapy. The current remedial measures recommended by the United States Food and Drug Administration (FDA) for non-adherence are generic and lack clinical evidence.

AIM

To assess remedial strategies for delayed or missed pregabalin doses in patients with epilepsy using Monte Carlo simulations.

METHOD

Monte Carlo simulations were performed using a published population pharmacokinetic model for pregabalin. The applicability of five proposed remedial regimens as well as FDA recommendations was evaluated by simulating various poor adherence scenarios in eight populations, including those with renal dysfunction.

RESULTS

All proposed remedial strategies were associated with delay duration and renal function. When delays are relatively short, an immediate regular dose is advised. The cut-off time points for taking the regular dose as a remedial regimen were 1, 2, 4, and 12 h for patients with mild renal impairment and normal renal function, moderate renal impairment, severe renal impairment, and end-stage renal disease, respectively. However, when delay aligns closely with a dosing interval, a regular dose combined with a partial dose proves effective. Generally, supplementing 1.3-fold the regular dose at the next scheduled time adequately compensates for the missed dose.

CONCLUSION

Model-based simulations provided quantitative evidence for the effectiveness and feasibility of remedial strategies for missed or delayed pregabalin doses.

Population pharmacokinetics of topiramate in Chinese children with epilepsy

OBJECTIVE

Topiramate, a broad-spectrum antiepileptic drug, exhibits substantial inter-individual variability in both its pharmacokinetics and therapeutic response. The aim of this study was to investigate the influence of patient characteristics and genetic variants on topiramate clearance using population pharmacokinetic (PPK) models in a cohort of Chinese pediatric patients with epilepsy.

METHOD

The PPK model was constructed using a nonlinear mixed-effects modeling approach, utilizing a dataset comprising 236 plasma concentrations of topiramate obtained from 181 pediatric patients with epilepsy. A one-compartment model combined with a proportional residual model was employed to characterize the pharmacokinetics of topiramate. Covariate analysis was performed using forward addition and backward elimination to assess the influence of covariates on the model parameters. The model was thoroughly evaluated through goodness-of-fit analysis, bootstrap, visual predictive checks, and normalized prediction distribution errors. Monte Carlo simulations were utilized to devise topiramate dosing strategies.

RESULT

In the final PPK models of topiramate, body weight, co-administration with oxcarbazepine, and a combined genotype of GKIR1-UGT (GRIK1 rs2832407, UGT2B7 rs7439366, and UGT1A1 rs4148324) were identified as significant covariates affecting the clearance (CL). The clearance was estimated using the formulas CL (L/h) = 0.44 × (BW⁄11.7)0.82 × eOXC for the model without genetic variants and CL (L/h) = 0.49 × (BW⁄11.7)0.81 × eOXC × eGRIK1-UGT for the model incorporating genetic variants. The volume of distribution (Vd) was estimated using the formulas Vd (L) = 6.6 × (BW⁄11.7). The precision of all estimated parameters was acceptable. Furthermore, the model demonstrated good predictability, exhibiting stability and effectiveness in describing the pharmacokinetics of topiramate.

CONCLUSION

The clearance of topiramate in pediatric patients with epilepsy may be subject to the influence of factors such as body weight, co-administration with oxcarbazepine, and genetic polymorphism. In this study, PPK models were developed to better understand and account for these factors, thereby improving the precision and individualization of topiramate therapy in children with epilepsy.

Simulations of topiramate dosage recommendations for poor compliance events

PURPOSE

To determine the influences of one or two consecutive missed topiramate (TPM) doses on TPM pharmacokinetics and to suggest the proper TPM replacement dosing schemes using Monte Carlo simulations.

METHODS

Monte Carlo simulations were performed for various replacement dosing schemes using the parameters from the published population pharmacokinetic models. The lowest percentage of deviation of simulated concentrations outside the reference range of 5-20 mg/L from the compliance scenario for each replacement dosing scheme was used as a criterion for choosing the proper replacement dosing scheme.

RESULTS

For the one missed dose, the replacement with an immediate regular dose and a partial dose resulted in the lowest and highest percentages of concentration below 5 mg/L, respectively. While the opposite results were observed for the upper bound of the reference range (20 mg/L). For the two consecutive missed doses, the replacement with one and a half-missed doses resulted in a lower percentage of deviation of concentrations below 5 mg/L from the compliance scenario than the replacement with one regular dose.

CONCLUSIONS

For the one missed dose, taking an immediate regular dose might be suitable for patients who require higher TPM levels, while for patients who require lower TPM levels, an immediate partial dose could be used. For the two consecutive missed doses, an immediate one and a half regular dose might be suitable. However, these results were merely based on simulations; thus, they should be used alongside the clinician's justification based on seizure control.

Should patients skip late doses of medication? A pharmacokinetic perspective

Missed doses, late doses, and other dosing irregularities are major barriers to effective pharmacotherapy, especially for the treatment of chronic conditions. What should a patient do if they did not take their last dose at the prescribed time? Should they take it late or skip it? In this paper, we investigate the pharmacokinetic effects of taking a late dose. We consider a single compartment model with linear absorption and elimination for a patient instructed to take doses at regular time intervals. We suppose that the patient forgets to take a dose and then realizes some time later and must decide what remedial steps to take. Using mathematical analysis, we derive several metrics which quantify the effects of taking the dose late. The metrics involve the difference between the drug concentration time courses for the case that the dose is taken late and the case that the dose is taken on time. In particular, the metrics are the integral of the absolute difference over all time, the maximum of the difference, and the maximum of the integral of the difference over any single dosing interval. We apply these general mathematical formulas to levothyroxine, atorvastatin, and immediate release and extended release formulations of lamotrigine. We further show how population variability can be immediately incorporated into these results. Finally, we use this analysis to propose general principles and strategies for dealing with dosing irregularities.

Designing Drug Regimens that Mitigate Nonadherence

Medication adherence is a well-known problem for pharmaceutical treatment of chronic diseases. Understanding how nonadherence affects treatment efficacy is made difficult by the ethics of clinical trials that force patients to skip doses of the medication being tested, the unpredictable timing of missed doses by actual patients, and the many competing variables that can either mitigate or magnify the deleterious effects of nonadherence, such as pharmacokinetic absorption and elimination rates, dosing intervals, dose sizes, and adherence rates. In this paper, we formulate and analyze a mathematical model of the drug concentration in an imperfectly adherent patient. Our model takes the form of the standard single compartment pharmacokinetic model with first-order absorption and elimination, except that the patient takes medication only at a given proportion of the prescribed dosing times. Doses are missed randomly, and we use stochastic analysis to study the resulting random drug level in the body. We then use our mathematical results to propose principles for designing drug regimens that are robust to nonadherence. In particular, we quantify the resilience of extended release drugs to nonadherence, which is quite significant in some circumstances, and we show the benefit of taking a double dose following a missed dose if the drug absorption or elimination rate is slow compared to the dosing interval. We further use our results to compare some antiepileptic and antipsychotic drug regimens.

What should patients do if they miss a dose of medication? A theoretical approach

Medication adherence is a major problem for patients with chronic diseases that require long term pharmacotherapy. Many unanswered questions surround adherence, including how adherence rates translate into treatment efficacy and how missed doses of medication should be handled. To address these questions, we formulate and analyze a mathematical model of the drug concentration in a patient with imperfect adherence. We find exact formulas for drug concentration statistics, including the mean, the coefficient of variation, and the deviation from perfect adherence. We determine how adherence rates translate into drug concentrations, and how this depends on the drug half-life, the dosing interval, and how missed doses are handled. While clinical recommendations require extensive validation and should depend on drug and patient specifics, as a general principle our theory suggests that nonadherence is best mitigated by taking double doses following missed doses if the drug has a long half-life. This conclusion contradicts some existing recommendations that cite long drug half-lives as the reason to avoid a double dose after a missed dose. Furthermore, we show that a patient who takes double doses after missed doses can have at most only slightly more drug in their body than a perfectly adherent patient if the drug half-life is long. We also investigate other ways of handling missed doses, including taking an extra fractional dose following a missed dose. We discuss our results in the context of hypothyroid patients taking levothyroxine.

Use of extended-release and immediate-release anti-seizure medications with a long half-life to improve adherence in epilepsy: A guide for clinicians

Poor adherence to anti-seizure medications (ASMs) is associated with breakthrough seizures and potentially increased toxicity in patients with epilepsy. Extended-release (ER) drugs and immediate-release (IR) drugs with a long half-life (t_1/2) that permit once-daily dosing (such as, perampanel, zonisamide, lamotrigine [IR, ER] and topiramate [ER]) have a number of advantages over short t_1/2 ASMs that require multiple daily dosing. These advantages include simplification of dosing regimens, reduction in pill burden, and a decrease in the peak-to-trough fluctuations in serum drug concentration that may be associated with a decreased risk of adverse effects and seizures. Such properties have wider implications in improving patient adherence to treatment. This article is intended as a practical guide for clinicians that provides an overview of the features of ER ASMs and long t_1/2 IR ASMs that are advantageous in the context of patient adherence and pharmacokinetic "forgiveness" (after missing a dose). In addition, we note that efforts to improve adherence should not depend solely on drug dosing regimens and drug pharmacokinetics, but should be part of a wider strategy that includes therapeutic drug monitoring, improved healthcare provider-patient dialogue, patient education, and the use of "reminder" technology.

Changing the Drug Delivery System: Does It Add to Non-Compliance Ramifications Control? A Simulation Study on the Pharmacokinetics and Pharmacodynamics of Atypical Antipsychotic Drug

This study investigates the pharmacokinetic (PK) and pharmacodynamic (PD) consequences of shifting from Quetiapine fumarate immediate-release (IR) to extended-release (XR) formulation in non-adherent schizophrenia patients. Monte-Carlo simulations using population PK and PD models were implemented to predict the time course of plasma concentration and Brief Psychiatric Rating Scale (BPRS) scores following the oral administration of 200 mg Seroquel^® every 12 h and 400 mg Seroquel XR^® every 24 h in patients experiencing dose delay, omission or doubling. Parameters were computed and their distributions were compared using the Kolmogorov–Smirnov test. Dose irregularities with both formulations had different effects on plasma concentration and %reduction in BPRS scores from baseline. However, the odds ratio of getting a %reduction in BPRS below 14%, or plasma concentration exceeding 500 µg/L, were comparable for adherent and non-adherent patients. Plasma therapeutic concentration after treatment cessation was maintained for <24 h in 48% and 29.6% of patients, and a steady state recovery time of <48 h was achieved in 51% and 13.4% of patients on the IR and XR formulations, respectively. Monte-Carlo simulations predict that the risks associated with the IR dose irregularities are not worsened when the XR formulation is used instead. Non-adherence events involving a single dose of either formulation do not require rescue doses.

Remedial dosing recommendations for delayed or missed doses of lamotrigine in pediatric patients with epilepsy using Monte Carlo simulations

OBJECTIVE

This study investigated the effect of delayed or missed doses on the pharmacokinetics (PK) of lamotrigine (LTG) in children with epilepsy and established remedial dosing recommendations for nonadherent patients.

METHODS

The Monte Carlo simulation based on a published LTG population PK model was used to assess the effect of different scenarios of nonadherence and the subsequently administered remedial regimens. The following three remedial approaches were investigated for each delayed dose: A) A partial dose was administered immediately, and the regular dose was administered at the next scheduled time. B) The delayed dose was administered immediately, followed by a partial dose at the next scheduled time. C) The delayed and partial doses were coadministered immediately, the next scheduled dose was skipped, and the regular dosing was resumed at the subsequent scheduled time. The most appropriate remedial regimen was that with the shortest deviation time from the individual therapeutic window.

RESULTS

The effect of nonadherence on PK was dependent on the delay duration and daily dose, and the recommended remedial dose was related to the delay duration and concomitant antiepileptic drugs. Remedial dosing strategies A and B were almost equivalent, whereas C showed a larger PK deviation time. If one dose was missed, double doses were not recommended for the next scheduled time.

CONCLUSIONS

Simulations provide quantitative insight into the remedial regimens for nonadherent patients, and clinicians should select the optimal regimen based on the status of patients.

Current Status of Antiepileptic Drugs as Preventive Migraine Therapy

BACKGROUND

Antiepileptic drugs (AEDs) are an important class of agents used in the treatment of migraine, a neurological disorder that imparts significant socioeconomic burden. It is important for neurologists to understand the rationale for AEDs in migraine-preventive treatment, as well as each agent's efficacy and tolerability profile, in order to best determine clinical care.

PURPOSE OF THIS REVIEW

This article specifically provides the following: (1) a review of the mechanism of action, efficacy, and tolerability of topiramate and divalproex sodium/sodium valproate, the most widely used AEDs for migraine prevention, (2) a discussion on emerging evidence regarding the efficacy of zonisamide and levetiracetam, and (3) comments on gabapentin, pregabalin, carbamazepine, oxcarbazepine, and lamotrigine, AEDs which have insufficient evidence for use in migraine prevention.

RECENT FINDINGS

The potential role for new extended-release formulations of topiramate in migraine prevention is discussed. There is substantial evidence supporting the use of AEDs in migraine prevention. Specific agents should be chosen based on their efficacy and tolerability profiles. Further studies are needed to determine the efficacy of the newer AEDs, zonisamide and levetiracetam, in migraine prevention and to clarify the role of gabapentinoids in headache management.

Approval of modified-release products by FDA without clinical efficacy/safety studies: A retrospective survey from 2008 to 2017

In principle, approval of a modified-release (MR) drug product is based on evidence from pharmacokinetic (PK) and/or pharmacodynamic studies and clinical efficacy/safety studies. The purpose of this survey is (i) to explore the number of new drug applications (NDAs) of MR drug products, approved by the FDA, employ the PK study as a bridge to already-approved immediate-release drug products without conducting their own clinical efficacy/safety studies; and (ii) to understand the type of PK studies are required for such NDAs. To this end, we surveyed the approved records of MR drug products from 2008 to 2017 from the Drug@FDA website, and filtered pertinent information from FDA's assessment reports. A total of five out of 79 products were found. A single dose PK study was conducted to investigate the underlying drug release mechanisms in four of these products. For these products, the applicants also performed multiple dose PK equivalence studies, but the PK parameters used to support the equivalence were different among studies. Information regarding the exposure-response relationship was available for all selected products, which is fundamental for such cases. Although the difference in PK curve shapes is recognized as being critical for the clinical effectiveness, this evaluation was not performed in all selected cases, as indicated in FDA's assessment reports.

Real-world assessment of treatment with extended-release topiramate (Trokendi XR®) and comparison with previous immediate-release topiramate treatment

AIM

Examine clinical profile of extended-release topiramate (Trokendi XR^®) and compare treatment-emergent adverse events (TEAEs) associated with Trokendi XR versus previous immediate-release topiramate (TPM-IR) treatment.

PATIENTS & METHODS

Pilot retrospective study analyzing data extracted from medical charts of patients ≥6 years of age prescribed Trokendi XR.

RESULTS

Trokendi XR was the most commonly used to prevent migraine. The most common TEAEs recorded during topiramate treatment were cognitive symptoms (word-finding difficulty, attention/concentration difficulty, slowed thinking), paresthesia, gastrointestinal problems and decreased appetite/weight loss. TEAE incidence was significantly (p < 0.001) lower during Trokendi XR versus previous TPM-IR treatment.

CONCLUSION

Trokendi XR use and outcomes in clinical practice were consistent with established profile of topiramate. Results supported the potential for better tolerability of Trokendi XR versus TPM-IR.

A Clinician's Guide to Oral Extended-Release Drug Delivery Systems in Epilepsy

Epilepsy is one of the most common chronic neurologic disorders that affects individuals of all ages. It is primarily managed with antiepileptic drugs (AEDs), with the goal of maintaining complete seizure control combined with minimal or no adverse effects. Oral administration is the mainstay of AED delivery for patients with chronic epilepsy and consists essentially of immediate-release (IR) and modified-release (delayed-release and extended-release [ER]) dosage formulations. Extended-release formulations (hydrophilic or hydrophobic matrix systems, reservoir systems, and osmotic-release systems) release a drug in a controlled manner during an extended period of time following administration. Extended-release formulations have many advantages compared with IR formulations, including simplification of dosing regimens, reduction in pill burden, and reduction in the peak-to-trough fluctuations in serum drug concentration that may be associated with a decreased risk of adverse effects and of seizures. These advantages have the potential to increase adherence to antiepileptic therapy, improve the quality of life of patients, and reduce health care costs. This article, which is intended as a practical guide for clinicians, reviews the properties of the different ER AED formulations currently available and discusses the advantages of ER over IR formulations. Subsequently, an explanation of the technologic basis of the different oral ER formulations, the critical attributes that differentiate ER products, and their individual strengths and weaknesses is provided. Specific recommendations to practitioners on treating patients with ER formulations are included.

Regularity of self-reported daily dosage of mood stabilizers and antipsychotics in patients with bipolar disorder

BACKGROUND

Polypharmacy is often prescribed for bipolar disorder, yet medication non-adherence remains a serious problem. This study investigated the regularity in the daily dosage taken of mood stabilizers and second generation antipsychotics.

METHODS

Daily self-reported data on medications taken and mood were available from 241 patients with a diagnosis of bipolar disorder who received treatment as usual. Patients who took the same mood stabilizer or second generation antipsychotic for ≥ 100 days were included. Approximate entropy was used to determine serial regularity in daily dosage taken. Generalized estimating equations were used to estimate if demographic or clinical variables were associated with regularity.

RESULTS

There were 422 analysis periods available from the 241 patients. Patients took drugs on 84.4% of days. Considerable irregularity was found, mostly due to single-day omissions and dosage changes. Drug holidays (missing 3 or more consecutive days) were found in 35.8% of the analysis periods. Irregularity was associated with an increasing total number of psychotropic drugs taken (p = 0.009), the pill burden (p = 0.026), and the percent of days depressed (p = 0.049).

CONCLUSION

Despite low missing percent of days, daily drug dosage may be irregular primarily due to single day omissions and dosage changes. Drug holidays are common. Physicians should expect to see partial adherence in clinical practice, especially with complex drug regimens. Daily dosage irregularity may impact the continuity of drug action, contribute to individual variation in treatment response, and needs further study.

Extended-release drug formulations for the treatment of epilepsy

INTRODUCTION

Extended-release (ER) preparations are either available or have been tested for several antiepileptic drugs (AEDs). Indeed, they may be helpful in improving efficacy, tolerability, adherence, compared to the corresponding immediate release (IR) preparations available. The use of ER preparations has been advocated in women of childbearing age and is - depending on the drug - especially helpful in patients who are treated in combination with enzyme inducing AEDs as well as in children.

AREAS COVERED

Clinical and pharmacokinetic studies on ER formulations of AEDs were identified by a PubMed literature research. Further references were added from the authors' personal knowledge and from the reference lists of the identified studies. Reviews and expert commentaries were included, where necessary.

EXPERT OPINION

Unfortunately, studies providing direct comparisons of ER and IR formulations of a given drug are only available for a handful of drugs. ER preparations are especially helpful in drugs with a short elimination half-life and concentration-depending efficacy and tolerability.

Topiramate in Migraine Prevention: A 2016 Perspective

BACKGROUND

In evidence-based guidelines published in 2000, topiramate was a third-tier migraine preventive with no scientific evidence of efficacy; recommendation for its use reflected consensus opinion and clinical experience. Its neurostabilizing activity, coupled with its favorable weight profile, made topiramate an attractive alternative to other migraine preventives that caused weight gain. When guidelines for migraine prevention in episodic migraine were published in 2012, topiramate was included as a first-line option based on double-blind, randomized controlled trials involving nearly 3000 patients. The scientific and clinical interest in topiramate has generated a large body of data from randomized controlled trials, meta-analyses, patient registries, cohort studies, and claims data analyses that have more fully characterized its role as a migraine preventive.

AIM

This article will review the profile of topiramate that has emerged out of the past decade of research and clinical use in migraine prophylaxis. It will also address the rationale for extended-release (XR) formulations in optimizing topiramate therapy in migraine.

SUMMARY

Topiramate has activity at multiple molecular targets, which may account for why it is effective in migraine and most other, more specific, anticonvulsants are not. Based on randomized controlled trials, topiramate reduces migraine frequency and acute medication use, improves quality of life, and reduces disability in patients with episodic migraine and in those with chronic migraine with or without medication overuse headache. Its efficacy in chronic migraine is not improved by the addition of propranolol. Topiramate's ability to prevent progression from high-frequency episodic migraine to chronic migraine remains unclear. Consistent with clinicians' perceptions, migraineurs are more sensitive to topiramate-associated side effects than patients with epilepsy. Paresthesia is a common occurrence early in treatment but is rarely cause for terminating topiramate treatment. Cognitive problems occur much less frequently than paresthesia but are more troublesome in terms of treatment discontinuation. Cognitive complaints can often be managed by slowly increasing the topiramate dose in small increments to allow habituation. As with other carbonic anhydrase inhibitors, topiramate has metabolic effects that favor the development of metabolic acidosis and possibly renal stones. Because migraineurs have an increased risk of renal stones independent of topiramate exposure, clinicians should counsel all migraine patients to maintain hydration. Abrupt onset of blurring, other visual disturbances, and/or ocular pain following topiramate's initiation should be evaluated promptly since this may indicate rare but potentially sight-threatening idiosyncratic events. Postmarketing evidence has shown that first-trimester exposure to topiramate monotherapy is associated with increased occurrence of cleft lip with or without cleft palate (Pregnancy Category D). Even though topiramate's long half-life would seemingly support q.d. dosing, randomized controlled migraine trials used b.i.d. administration of immediate-release (IR) topiramate, which has more favorable plasma concentration-time profile (ie, lower peak concentrations and higher trough concentrations) than q.d. IR dosing. Given the sensitivity of migraineurs to topiramate-related adverse events, particularly cognitive effects, pharmacokinetic profiles should be considered when optimizing migraine outcomes. The extended-release (XR) formulations Qudexy^® XR (Upsher-Smith Laboratories) and Trokendi XR^® (Supernus Pharmaceuticals) were specifically designed to achieve the adherence benefits of q.d. dosing but with more favorable (ie, more constant) steady-state plasma concentrations over the 24-hour dosing interval vs IR topiramate b.i.d. Intriguing results from a study in healthy volunteers showed consistently less impairment in neuropsychometric tests of verbal fluency and mental processing speed with an XR topiramate formulation (Trokendi XR) vs IR topiramate b.i.d. These findings suggest a pharmacodynamic effect associated with significantly reducing plasma concentration fluctuation when topiramate absorption is slowed. Results of retrospective studies in migraineurs treated with XR topiramate appear to support a clinically meaningful benefit of XR topiramate vs IR topiramate in terms of significantly fewer cognitive effects, improved adherence, and overall better outcomes of migraine prophylaxis with topiramate.

Assessing bioequivalence of generic modified-release antiepileptic drugs

OBJECTIVES

The purpose of this study was to determine how closely generic modified-release antiepileptic drugs (MR-AEDs) resemble reference (brand) formulations by comparing peak concentrations (Cmax), total absorption (area under the curve [AUC]), time to Cmax (Tmax), intersubject variability, and food effects between generic and reference products.

METHODS

We tabulated Cmax and AUC data from the bioequivalence (BE) studies used to support the approvals of generic Food and Drug Administration-approved MR-AEDs. We compared differences in 90% confidence intervals of the generic/reference AUC and Cmax geometric mean ratios, and intersubject variability, Tmax and delivery profiles and food effects.

RESULTS

Forty-two MR-AED formulations were studied in 3,175 healthy participants without epilepsy in 97 BE studies. BE ratios for AUC and Cmax were similar between most generic and reference products: AUC ratios varied by >15% in 11.4% of BE studies; Cmax varied by >15% in 25.8% of studies. Tmax was more variable, with >30% difference in 13 studies (usually delayed in the fed compared to fasting BE studies). Generic and reference MR products had similar intersubject variability. Immediate-release AEDs showed less intersubject variability in AUC than did MR-AEDs.

CONCLUSIONS

Most generic and reference MR-AEDs have similar AUC and Cmax values. Ratios for some products, however, are near acceptance limits and Tmax values may vary. Food effects are common with MR-AED products. High variability in pharmacokinetic values for once-a-day MR-AEDs suggests their major advantage compared to immediate-release AED formulations may be the convenience of less frequent dosing to improve adherence.