Identification of adverse reactions that can occur on substitution of generic for branded lamotrigine in patients with epilepsy

Evaluating the bioequivalence of levetiracetam brand and generic oral tablets available in the Saudi market in vivo

Background

Epilepsy is a common global neurological disorder. About 30% of epileptic patients are managed with anti-epileptic Drugs (AEDs). Since 2000, Levetiracetam (LEV) has been marketed around the world as an AED under the brand name Keppra, and recently more generics are found in the Saudi market as cheaper alternatives. The objective of this study is to evaluate the bioequivalence of LEV brand and generics available in the Saudi market in mice.

Methods

Pharmacokinetics (PK), liver function test, and behavioral studies were conducted for LEV brand and generic in different groups of Blab/c mice.

Results

PK results show a significance difference in PK parameters mostly evidenced with generic 3, then generic 2. The only significant different between Keppra and generic 1 was in T1/2. In addition, Keppra did not significantly increase liver enzymes in comparison to other generics. On the other hand, other generics showed less favorable results in increasing liver enzymes. Keppra reduced the number and intensity of epileptic attacks, had no mortality rate due to epilepsy, and was associated with less sever seizures attacks.

Conclusion

Keppra, the brand form of LEV, has better safety and efficacy profiles in mice compared to 3 generics found in the Saudi market. Therefore, we recommend evaluating the same parameters tested in this study in patients utilizing similar generics and brand to establish the existence of bioequivalence between LEV brand and generics.

Therapeutic Basis of Generic Substitution of Antiseizure Medications

More than thirty antiseizure medications (ASMs) are available for treating epilepsy. ASMs differ in their potency and efficacy in controlling seizures by acting on diverse targets in the brain, often with variable pharmacokinetics. Moreover, nearly 30% of people with epilepsy have drug-resistant or intractable seizures. Generic substitution of ASMs is a complex issue. It is thought that frequent generic substitution in people with epilepsy may cause problems because the U.S. Food and Drug Administration (FDA) rules allow too much variability across products. The standard bioequivalence range (80% to 125%) appears too broad for many ASMs, especially those exhibiting little separation between therapeutic and toxic levels. Hence, sub-therapeutic concentration may lead to therapeutic failure with seizure recurrence, which could be life threatening. A supra-therapeutic level could result in adverse effects or compliance issues. There are reported issues with generic substitutions of phenytoin, topiramate, levetiracetam, carbamazepine, and lamotrigine. There is discussion in the epilepsy community about additional guidelines, including designation of generic ASMs as Narrow Therapeutic Index (NTI) drugs and how patient education plays a role in generic substitution. Overall, based on the published evidence on specific generic ASMs, FDA bioequivalence standards are not the cause of problems with generic ASM substitution. Rather, it is imperative that physicians and pharmacists provide adequate patient education on what to expect when switching to generic ASMs, including changes in medication shape and color. Another suggestion would be to consider that all ASMs be considered for inclusion in NTI class to prevent the clinical outcome issues associated with generic ASM switching. SIGNIFICANCE STATEMENT: There are critical aspects to consider when switching from a brand name antiseizure medication (ASM) when a generic becomes available or switching between generics. Generic ASMs are interchanged with little consideration of differences in therapeutic equivalence and other clinical factors. This article describes key issues on generic substitution of ASMs and highlights critical pharmacotherapeutic issues associated with generic ASMs.

Quantification of Adverse Drug Reactions Related to Drug Switches in The Netherlands

We performed a retrospective cohort study in the Dutch patient population to identify active substances with a relatively high number of adverse drug reactions (ADRs) potentially related to drug switching. For this, we analyzed drug switches and reported ADRs related to switching between June 1, 2009, and December 31, 2016, for a selection of 20 active substances. We also compared pharmacovigilance analyses based on the absolute, switch-corrected, and user-corrected numbers of ADRs. In total, 1,348 reported ADRs and over 23.8 million drug switches were obtained from the National Health Care Institute in The Netherlands and from Lareb, which is The Netherlands Pharmacovigilance Centre. There was no correlation between the number of ADRs and the number of switches, but, on average, we found 5.7 reported ADRs per 100,000 switches. The number was relatively high for rivastigmine, levothyroxine, methylphenidate, and salbutamol, with 74.9, 50.9, 47.6, and 26.1 ADRs per 100,000 switches, respectively. When comparing analyses using the absolute number and the switch-corrected number of ADRs, we demonstrate that different active substances would be identified as having a relatively high number of ADRs, and different time periods of increased numbers of ADRs would be observed. We also demonstrate similar results when using the user-corrected number of ADRs instead of the switch-corrected number of ADRs, allowing for a more feasible approach in pharmacovigilance practice. This study demonstrates that pharmacovigilance analyses of switch-related ADRs leads to different results when the number of reported ADRs is corrected for the actual number of drug switches.

Switching medication products during the treatment of psychiatric illness

BACKGROUND

The common practice of switching between branded (reference) medications and their corresponding generic products, between generic products, or even from a generic product to a branded medication during the treatment of central nervous system (CNS) disorders may compromise efficacy and/or tolerability.

METHODS

We assessed the published literature from March 1, 2010 through June 30, 2017 via PubMed using the MeSH term 'generics, drugs' alone and in combination with class-specific terms (e.g., 'anticonvulsants', 'mood stabilisers'), for studies detailing outcomes following product switches.

RESULTS

Although some studies comparing the initiation of reference versus generic drugs suggest equivalence between products, several studies detailing a switch between reference and generic products describe reductions in efficacy, reduced medication adherence and persistence, and increased overall health care resource utilization and costs associated with generic substitution.

CONCLUSION

When product switches are considered, they should only proceed with the full knowledge of both patient and provider.

Generic Drugs in the United States: Policies to Address Pricing and Competition

The cost of prescription drugs in the United States continues to be a source of concern for patients, caregivers, and policymakers. Drug prices typically decline rapidly once generic drugs receive US Food and Drug Administration (FDA) approval and enter the market, but the past decade has witnessed rising costs and shortages of generic drugs. We describe the strategies used by brand-name manufacturers to undermine generic competition and the reasons underlying the price increases of off-patent drugs, some of which continue to lack any competition from generic versions, and others that have increased in price despite having generic versions. We discuss the FDA's role in addressing drug prices and promoting competition, including recent agency policies to modify its process of reviewing generic drug applications and to prioritize applications for off-patent drugs with few competitors. We also examine proposed policy solutions and research areas that could help address the price increases of off-patent drugs.

Determination of lamotrigine in human plasma using liquid chromatography-tandem mass spectrometry

Aim

Lamotrigine (LTG) is a widely used anti‐epileptic drug that is administered to avoid seizures and to maintain seizure‐free status. However, several factors reportedly cause individual differences of plasma LTG levels, and the therapeutic target range of LTG varies between individuals. Thus, to optimize effective doses of LTG, we developed a rapid and simple method for determining plasma LTG concentrations.

Methods

Lamotrigine and the internal standard papaverine were extracted from human plasma using solid‐phase extraction. After filtration, 5‐μL aliquots of final samples were injected into the liquid chromatography‐tandem mass spectrometry instrument and LTG and internal standard were separated using a Cadenza CD‐C18 column (100 × 2 mm, 3 μm) with 0.1% formic acid in water/acetonitrile (2/1, v/v).

Results

The calibration curve was linear from 0.2 to 5.0 μg/mL, and assessments of recovery, intra‐ and inter‐day precision and accuracy, matrix effects, freeze and thaw stability, and long‐term stability demonstrated good reproducibility. Retention times of LTG and internal standard were 1.6 and 2.0 minutes, respectively, and the total run time was 3.5 minutes for each sample.

Conclusion

We developed a rapid and simple method for determining plasma LTG concentrations. The present novel system could be used to inform LTG dose adjustments for individual patients.

We developed a rapid and simple method for determining plasma concentrations of LTG showing good validation for a relatively wide range (0.2‐5.0 μg/mL). The present method can inform estimates of plasma concentrations of LTG to clinicians within 1 hour of sample collection.

Which information on women's issues in epilepsy does a community pharmacist need to know? A Delphi consensus study

OBJECTIVE

The aim of this study was to develop and achieve consensus on a core list of important knowledge items that community pharmacists should know on women's issues in epilepsy.

METHODS

This was a consensual study using a modified Delphi technique. Knowledge items were collected from the literature and from nine key contacts who were interviewed on their views on what information community pharmacists should have on women's issues in epilepsy. More knowledge items were suggested by five researchers with interest in women's issues who were contacted to rate and comment on the knowledge items collected. Two iterative Delphi rounds were conducted among a panel of pharmacists (n=30) to achieve consensus on the knowledge items to be included in the core list. Ten panelists ranked the knowledge items by their importance using the Analytical Hierarchy Process (AHP).

RESULTS

Consensus was achieved to include 68 knowledge under 13 categories in the final core list. Items ranked by their importance were related to the following: teratogenicity (10.3%), effect of pregnancy on epilepsy (7.4%), preconception counseling (10.3%), bone health (5.9%), catamenial epilepsy (7.4%), menopause and hormonal replacement therapy (2.9%), contraception (14.7%), menstrual disorders and infertility (8.8%), eclampsia (2.9%), breastfeeding (4.4%), folic acid and vitamin K (5.9%), counseling on general issues (14.7%), and sexuality (4.4%).

CONCLUSION

Using consensual knowledge lists might promote congruence in educating and/or training community pharmacists on women's issues in epilepsy. Future studies are needed to investigate if such lists can improve health services provided to women with epilepsy (WWE).

Association between switching antiepileptic drug products and healthcare utilization: A systematic review

AIMS

There is ongoing concern whether switching between different antiepileptic drug (AED) products may compromise patient care. We systematically reviewed changes in healthcare utilization following AED switch.

METHODS

We searched MEDLINE and EMBASE databases (1980-October 2016) for studies that assessed the effect of AED switching in patients with epilepsy on outpatient visits, emergency room visits, hospitalization and hospital stay duration.

RESULTS

A total of 14 articles met the inclusion criteria. All were retrospective studies. Four provided findings for specific AEDs only (lamotrigine, topiramate, phenytoin and divalproex), 9 presented pooled findings from multiple AEDs, and 1 study provided both specific (lamotrigine, topiramate, oxcarbazepine, and levetiracetam) and pooled findings. Three studies found an association between a switch of topiramate and an increase in healthcare utilization. Another three studies found that a brand-to-generic lamotrigine switch was not associated with an increased risk of emergently treated events (ambulance use, ER visits or hospitalization). The outcomes of the pooled AED switch studies were inconsistent; 5 studies reported an increased healthcare utilization while 5 studies did not.

CONCLUSION

Studies that have examined the association between an AED switch and a change in healthcare utilization report conflicting findings. Factors that may explain these inconsistent outcomes include inter-study differences in the type of analysis undertaken (pooled vs individual AED data), the covariates used for data adjustment, and the type of switch examined. Future medical claim database studies employing a prospective design are encouraged to address these and other factors in order to enhance inter-study comparability and extrapolation of findings.

Use of Therapeutic Drug Monitoring, Electronic Health Record Data, and Pharmacokinetic Modeling to Determine the Therapeutic Index of Phenytoin and Lamotrigine

BACKGROUND

Defining a drug's therapeutic index (TI) is important for patient safety and regulating the development of generic drugs. For many drugs, the TI is unknown. A systematic approach was developed to characterize the TI of a drug using therapeutic drug monitoring and electronic health record (EHR) data with pharmacokinetic (PK) modeling. This approach was first tested on phenytoin, which has a known TI, and then applied to lamotrigine, which lacks a defined TI.

METHODS

Retrospective EHR data from patients in a tertiary hospital were used to develop phenytoin and lamotrigine population PK models and to identify adverse events (anemia, thrombocytopenia, and leukopenia) and efficacy outcomes (seizure-free). Phenytoin and lamotrigine concentrations were simulated for each day with an adverse event or seizure. Relationships between simulated concentrations and adverse events and efficacy outcomes were used to calculate the TI for phenytoin and lamotrigine.

RESULTS

For phenytoin, 93 patients with 270 total and 174 free concentrations were identified. A de novo 1-compartment PK model with Michaelis-Menten kinetics described the data well. Simulated average total and free concentrations of 10-15 and 1.0-1.5 mcg/mL were associated with both adverse events and efficacy in 50% of patients, resulting in a TI of 0.7-1.5. For lamotrigine, 45 patients with 53 concentrations were identified. A published 1-compartment model was adapted to characterize the PK data. No relationships between simulated lamotrigine concentrations and safety or efficacy endpoints were seen; therefore, the TI could not be calculated.

CONCLUSIONS

This approach correctly determined the TI of phenytoin but was unable to determine the TI of lamotrigine due to a limited sample size. The use of therapeutic drug monitoring and EHR data to aid in narrow TI drug classification is promising, but it requires an adequate sample size and accurate characterization of concentration-response relationships.

Switching generic antiepileptic drug manufacturer not linked to seizures: A case-crossover study

OBJECTIVE

With more antiepileptic drugs (AED) becoming available in generic form, we estimated the risk of seizure-related events associated with refilling generic AEDs and the effect of switching between different manufacturers of the same generic drug.

METHODS

We designed a population-based case-crossover study using the Medicaid Analytic eXtract and a US commercial health insurance database. We identified 83,001 generic AED users who experienced a seizure-related hospital admission or emergency room visit between 2000 and 2013 and assessed whether they received a refill of the same AED from the same manufacturer or a different manufacturer. Patients served as their own controls and conditional logistic regression was used to compare exposure to a refill during the hazard period, defined as days 2-36 preceding the seizure-related event, to exposure during the control period, defined as days 51-85 preceding the seizure-related event.

RESULTS

Generic AED refilling was associated with an 8% increase in the odds of seizure-related events (odds ratio [OR] 1.08; 95% confidence interval [CI] 1.06-1.11). The OR following a switch to a different manufacturer of the same AED was 1.09 (95% CI 1.03-1.15); however, after adjusting for the process of refilling, there was no association between switching and seizure-related hospital visits (OR 1.00; 95% CI 0.94-1.07).

CONCLUSIONS

Among patients on a generic AED, refilling the same AED was associated with an elevated risk of seizure-related event; however, there was no additional risk from switching during that refill to a different manufacturer. Generic AEDs available to US patients, with Food and Drug Administration-validated bioequivalence, appear to be safe clinical choices.

Potential problems and recommendations regarding substitution of generic antiepileptic drugs: a systematic review of literature

Despite the availability of generic antiepileptic drugs (AEDs), still patients and neurologists hesitate to make a switch due to assorted reasons. The objectives of this review were to evaluate the risks associated with the generic substitution of AEDs. In this context, we also summarized the recommendations of various international societies to treat epileptic patients. We used a number of electronic databases to identify the relevant published studies which demonstrated the potential problems and recommendations regarding generic substitution of AEDs. Of 204 articles found initially, 153 were selected for additional review. Subsequently, 68 articles were finally selected. This review concluded that potential problems linked with the generic substitution of AEDs could be bioequivalence issues, failure of drug therapy, emergence of adverse events and increase in the frequency of seizures. The reasons could be the pharmacokinetics properties of AEDs and unique characteristics of some epilepsy patients. Consequently, the generic substitution of AEDs affects the successful treatment and quality of life of the patients. Various guidelines recommend the well-controlled epileptic patients to avoid switching from brand-to-generic products, generic-to-brand products or generic to some other generic products.

Generic lamotrigine versus brand-name Lamictal bioequivalence in patients with epilepsy: A field test of the FDA bioequivalence standard

OBJECTIVE

To test the current U.S. Food and Drug Administration (FDA) bioequivalence standard in a comparison of generic and brand-name drug pharmacokinetic (PK) performance in "generic-brittle" patients with epilepsy under clinical use conditions.

METHODS

This randomized, double-blind, multiple-dose, steady-state, fully replicated bioequivalence study compared generic lamotrigine to brand-name Lamictal in "generic-brittle" patients with epilepsy (n = 34) who were already taking lamotrigine. Patients were repeatedly switched between masked Lamictal and generic lamotrigine. Intensive PK blood sampling at the end of each 2-week treatment period yielded two 12-h PK profiles for brand-name and generic forms for each patient. Steady-state area under the curve (AUC), peak plasma concentration (Cmax ), and minimum plasma concentration (Cmin ) data were subjected to conventional average bioequivalence (ABE) analysis, reference-scaled ABE analysis, and within-subject variability (WSV) comparisons. In addition, generic-versus-brand comparisons in individual patients were performed. Secondary clinical outcomes included seizure frequency and adverse events.

RESULTS

Generic demonstrated bioequivalence to brand. The 90% confidence intervals of the mean for steady-state AUC, Cmax , and Cmin for generic-versus-brand were 97.2-101.6%, 98.8-104.5%, and 93.4-101.0%, respectively. The WSV of generic and brand were also similar. Individual patient PK ratios for generic-versus-brand were similar but not identical, in part because brand-versus-brand profiles were not identical, even though subjects were rechallenged with the same product. Few subjects had seizure exacerbations or tolerability issues with product switching. One subject, however, reported 267 focal motor seizures, primarily on generic, although his brand and generic PK profiles were practically identical.

SIGNIFICANCE

Some neurologists question whether bioequivalence in healthy volunteers ensures therapeutic equivalence of brand and generic antiepileptic drugs in patients with epilepsy, who may be at increased risk for problems with brand-to-generic switching. Bioequivalence results in "generic-brittle" patients with epilepsy under clinical conditions support the soundness of the FDA bioequivalence standards. Adverse events on generic were not related to the small, allowable PK differences between generic and brand.

Licensing of Generic Medicines: Are There Any Challenges Left? A Pharmaceutical Regulatory Perspective

When an innovative product (innovator) is not covered anymore by intellectual property rights, cheaper equivalent medicinal products (generic products) may be marketed and used in clinical practice. The regulation of generic products is well-established, and is primarily based on standard rules for quality, therapeutic equivalence requirements (the latter in most instances proven through a bioequivalence study), and safety data for the innovator. The extensive experience from bringing generic products to the market over the last decades allows the conclusion that they are well-accepted and provide a useful alternative option for cost-effective pharmacotherapy. While supporting this conclusion, there are a number of issues to be considered during the assessment of a generic product application. Six scenarios are described in total, from an efficacy and a safety perspective, where potential concerns with the current regulatory standards could arise in the approval of generic products. We also propose solutions to these scenarios in order to foster debate on these issues.

The impact on health outcomes and healthcare utilisation of switching to generic medicines consequent to reference pricing: the case of lamotrigine in New Zealand

BACKGROUND

Many countries have implemented generic reference pricing and substitution as methods of containing pharmaceutical expenditure. However, resistance to switching between medicines is apparent, especially in the case of anti-epileptic medicines.

OBJECTIVES

This study sought to exploit a nation-wide policy intervention on generic reference pricing in New Zealand to evaluate the health outcomes of patients switching from originator to generic lamotrigine, an anti-epileptic medicine.

METHODS

A retrospective study using the national health collections and prescription records was conducted comparing patients who switched from originator brand to generic lamotrigine with patients who remained on the originator brand. Primary outcome measures included switch behaviour, changes in utilisation of healthcare services at emergency departments, hospitalisations and use of specialist services, and mortality.

RESULTS

Approximately one-quarter of all patients using the originator brand of lamotrigine switched to generic lamotrigine, half of whom made the switch within 60 days of the policy implementation. Multiple switches (three or more) between generic and brand products were evident for around 10% of switchers. Switch-back rates of 3% were apparent within 30 days post-switch. No difference in heath outcome measures was associated with switching from originator lamotrigine to a generic equivalent and hence no increased costs could be found for switchers.

CONCLUSIONS

Switching from brand to generic lamotrigine is largely devoid of adverse health outcomes; however, creating an incentive to ensure a greater proportion of patients switch to generic lamotrigine is required to achieve maximal financial savings from a policy of generic reference pricing.

Bioequivalent antiepileptic drug switching and the risk of seizure-related events

BACKGROUND

Older antiepileptic drugs (AEDs) are known to have a narrow therapeutic index. As a consequence, switching between bioequivalent AEDs remains controversial in the management of epilepsy. We investigated the association between A-rated switching of each class of currently available AED and emergent treatment for a seizure-related event.

METHODS

We used a case-control method and claims data from the 2010 to 2011 Truven Health MarketScan(®) Commercial Claims Database to estimate the risk of seizure following a medication switch. Cases and controls with an epilepsy diagnosis were identified by emergency/inpatient or outpatient visit claims, respectively. Cases and controls (N=9110) were matched 1:1 by age, epilepsy diagnosis category and seizure medication. The exposure was defined as a switch between A-rated AEDs during the 90 days prior to index date. Conditional logistic regression was used to estimate the association, adjusting for gender, baseline Deyo-Charlson Comorbidity Index (0, 1, 2, or 3+), region (Northeast, Central, South, and West), and total AED medications.

RESULTS

A switch between A-rated AEDs occurred in 1053 (23.2%) cases and 827 (18.1%) matched controls. The unadjusted and adjusted odds ratios of a seizure-related event for switching were 1.38 (95% CI: 1.25-1.52) and 1.27 (95% CI: 1.14-1.41), respectively. The independent risk of an event also increased with each category increase in the Charlson score (CCI=1: 1.17, 95% CI: 1.02-1.33; CCI=2: 1.33, 95% CI: 1.09-1.62; CCI=3+: 1.99, 95% CI: 1.64-2.41). Older AEDs had infrequent switches compared to newer agents and were not associated with events.

DISCUSSION

We found a modest association between AED switching and seizure-related events. Our analysis suggests that the behavior of switching alone may lead to seizure-related events regardless of the medication or type of switch. Other disease or environmental characteristics may contribute to this association. Based on these and other findings, health care professionals and patients should be cautious about switching bioequivalent AEDs.

Generic substitution of antiepileptic drugs--a survey of patients' perspectives in Germany and other German-speaking countries

In this study, we sought to determine the patients' attitudes towards generic substitution of antiepileptic drugs (AEDs) and their experiences with the usage of generic antiepileptic drugs in Germany and other German-speaking countries. A questionnaire was designed for a cross-sectional study. Two thousand copies of the questionnaire were delivered with a magazine edited by a patients' organization. Additionally, the questionnaire was placed on the internet platform of another patients' organization. Thirty-two percent of the patients who already experienced a switch to generic AEDs complained of problems with the switch. Patients who answered the magazine survey worried significantly more about generic substitution of AEDs than patients who answered the internet version. Patients who had never switched were more concerned about generic substitution than those who had already switched. Moreover, patients' beliefs differed between the use of generic drugs in acute medical conditions such as pain and infections and the use of generic AEDs in epilepsy.

Generic substitution of lamotrigine among medicaid patients with diverse indications: a cohort-crossover study

BACKGROUND

Controversy exists about the safety of substituting generic antiepileptic drugs (AEDs). Lamotrigine, the prototypical newer AED, is often used for psychiatric and neurological conditions other than epilepsy. The safety of generic substitution of lamotrigine in diverse populations of AED users is unclear.

OBJECTIVE

The objective of this study was to evaluate potential associations between generic substitution of lamotrigine and adverse consequences in a population of diverse users of this drug.

STUDY DESIGN

This study was a retrospective cohort-crossover design using state Medicaid claims data from July 2006 through June 2009.

METHODS

Subjects were included in the cohort if they converted from brand to generic lamotrigine and had 2 years of lamotrigine use prior to conversion. The frequency of emergency department (ED) visits, hospitalizations and condition-specific ED visits or hospitalizations were recorded in the 60 days immediately following the conversion to generic lamotrigine, then compared with the incidence of the same events during a randomly selected time period indexed to one of the patient's past refills of branded lamotrigine. Multivariate conditional logistic regression was used to quantify the association between generic conversion and health services utilization while controlling for changes in lamotrigine dose and concurrent drug use.

RESULTS

Of the 616 unique subjects included in this analysis, epilepsy was the most common diagnosis (41%), followed by bipolar disorder (32%), pain (30%) and migraine (18%). Conversion to generic lamotrigine was not associated with a statistically significant increase in the odds of an ED visit (adjusted odds ratio [AOR] = 1.35; 95% confidence interval [CI] 0.92, 1.97), hospitalization (AOR = 1.21; 95% CI 0.60, 2.50) or condition-specific encounter (AOR 1.75; 95 CI 0.87, 3.51).

CONCLUSIONS

A statistically significant increase in ED visits, hospitalizations or condition-specific encounters was not observed following the switch from brand to generic lamotrigine, although a type II error cannot be ruled out.

Host factors affecting antiepileptic drug delivery-pharmacokinetic variability

Antiepileptic drugs (AEDs) are the mainstay in the treatment of epilepsy, one of the most common serious chronic neurological disorders. AEDs display extensive pharmacological variability between and within patients, and a major determinant of differences in response to treatment is pharmacokinetic variability. Host factors affecting AED delivery may be defined as the pharmacokinetic characteristics that determine the AED delivery to the site of action, the epileptic focus. Individual differences may occur in absorption, distribution, metabolism and excretion. These differences can be determined by genetic factors including gender and ethnicity, but the pharmacokinetics of AEDs can also be affected by age, specific physiological states in life, such as pregnancy, or pathological conditions including hepatic and renal insufficiency. Pharmacokinetic interactions with other drugs are another important source of variability in response to AEDs. Pharmacokinetic characteristics of the presently available AEDs are discussed in this review as well as their clinical implications.

Interchangeability among therapeutic equivalents of lamotrigine: evaluation of quality of life

Epilepsy is the most common serious neurological disorder worldwide. Approximately 70% of patients with epilepsy have their seizures controlled by clinical and pharmacological treatment. This research evaluated the possible influence of interchangeability among therapeutic equivalents of LTG on the clinical condition and quality of life of refractory epileptic patients. The study was divided into three periods of 42 days, and an equivalent therapeutic LTG randomly dispensed for each period (two similars - formulations A and B, and the reference product - formulation C). The mean dose of LTG was 5.5 mg/kg/day. The presence of side effects tends to have a greater deleterious effect on quality of life of refractory epileptics compared to variations in number of seizures or changes in plasma concentrations. The results showed that independently of the drug prescribed, interchangeability among therapeutic equivalents can negatively impact epilepsy control.

Clinical and pharmacy utilization outcomes with brand to generic antiepileptic switches in patients with epilepsy

PURPOSE

To determine if switching from select branded to generic equivalent antiepileptic drugs (AEDs) in patients with epilepsy is associated with adverse outcomes.

METHODS

A retrospective cohort study using a large health insurance plan claims database comparing patients with epilepsy who switched from brand to generic equivalent phenytoin, lamotrigine, or divalproex after 6 months (switch cohorts) to matched patients who remained on the brand (nonswitch cohorts). Primary outcomes measured include the incidence rate ratio (IRR) of discontinuation of the index AED; change in dose of index AED or addition of another AED; and the event rate ratio (ERR) of the composite of all-cause emergency department (ED) visits or hospitalizations.

KEY FINDINGS

Lamotrigine and divalproex showed no differences in AED utilization changes between the switchers and nonswitchers [IRR for lamotrigine 1.00, 95% confidence interval (CI) 0.84-1.19; IRR for divalproex 1.02, 95% CI, 0.88-1.42]. Compared with nonswitchers, the phenytoin switch cohort had greater incidence of AED utilization changes (IRR 1.85, 95% CI 1.50-2.29). The switch versus nonswitch cohorts did not demonstrate differences in ED visits or hospitalizations for the studied AEDs (ERR for phenytoin 0.96, 95% CI 0.80-1.16; ERR for lamotrigine 0.97, 95% CI 0.80-1.17; ERR for divalproex 0.83, 95% CI 0.66-1.06).

SIGNIFICANCE

Brand to generic switching of phenytoin was not associated with more clinical events but was associated with increased index drug discontinuations, dose changes, or therapy augmentations. Lamotrigine or divalproex brand to generic switching was not associated with increased incidence of events or utilization changes compared with patients remaining on the branded product. Changes in AED utilization may be more sensitive than ED visits and hospitalizations for detecting adverse outcomes.

Comparison of dissolution profiles and serum concentrations of two lamotrigine tablet formulations

Objective: The aim of this study was to investigate the extent of variations in lamotrigine serum concentrations between two immediate-release tablet formulations. Data were compared with in vitro difference and similarity tests on dissolution profiles of the two formulations.

Methods: Dissolution characteristics of formulations A (reference) and B (test) were evaluated at three points spanning the physiologic pH range (pH 1.2, pH 4.5, pH 6.8). A model-independent approach of difference (f1) and similarity (f2) tests were applied to dissolution data. A clinical study was performed with 16 patients who were divided into two groups — one group received formulation A (n=9) and the other received formulation B (n=7). Lamotrigine steady-state concentrations were determined by high-performance liquid chromatography on a reverse-phase column.

Results: There were no statistically significant differences in lamotrigine serum concentrations between the two groups, although formulation B had slightly higher mean concentration values (formulation A: 3.97±4.1 μg/mL; formulation B: 5.78±2.7 μg/mL). Dissolution profiles of the two formulations were similar in the pH 1.2 dissolution medium; however, the dissolution profiles of formulation B were outside the dissolution limit (≥85% at 15 minutes) in the pH 4.5 and 6.8 dissolution media.

Conclusions: No significant changes in the serum concentrations of lamotrigine were seen between the two investigated formulations. There is no evidence to suggest that the differences in dissolution profiles at pH 4.5 and pH 6.8 affect the therapeutic efficacy of the formulations. It is evident that the doses of test formulation given to the patients were higher as a consequence of common assumption that generic products have a lower absorption rate, which is proven unnecessary in this study. This investigation was a pilot study and thus further investigations with a larger sample size are necessary to determine if there is a connection between dissolution profiles and the therapeutic effect of investigated formulations.

Switching from brand-name to generic psychotropic medications: a literature review

Generic medications do not undergo the rigorous approval process required of original medications. Their effectiveness and safety is expected to be equal to that of their more expensive counterparts. However, several case reports and studies describe clinical deterioration and decreased tolerability with generic substitution. Pubmed was searched from January 1, 1974 to March 1, 2010. The MeSH term "generic, drugs" was combined with "anticonvulsants," "mood stabilizers," "lithium," "antidepressants," "antipsychotics," "anxiolytics," and "benzodiazepines." Additional articles were obtained by searching the bibliographies of relevant references. Articles in English, French, or Spanish were considered if they discussed clinical equivalence of generic and brand-name medications, generic substitution, or issues about effectiveness, tolerability, compliance, or economics encountered with generics. Clinical deterioration, adverse effects, and changes in pharmacokinetics are described with generic substitution of several anticonvulsants/mood stabilizers (carbamazepine, valproate, lamotrigine, gabapentin, topiramate, lithium), antidepressants (amitriptyline, nortriptyline, desipramine, fluoxetine, paroxetine, citalopram, sertraline, venlafaxine, mirtazapine, bupropion), antipsychotics (risperidone, clozapine), and anxiolytics (clonazepam, alprazolam). Generics do not always lead to the anticipated monetary savings and also raise compliance issues. Although the review is limited by publication bias and heterogeneity of the studies in the literature, we believe there is enough concern to advise generic switching on an individual basis with close monitoring throughout the transition. Health professionals should be aware of the stakes around generic substitution especially when health economics promote universal use of generics.

Seizure outcomes following the use of generic versus brand-name antiepileptic drugs: a systematic review and meta-analysis

The automatic substitution of bioequivalent generics for brand-name antiepileptic drugs (AEDs) has been linked by anecdotal reports to loss of seizure control. To evaluate studies comparing brand-name and generic AEDs, and determine whether evidence exists of superiority of the brand-name version in maintaining seizure control. English-language human studies identified in searches of MEDLINE, EMBASE and International Pharmaceutical Abstracts (1984 to 2009). Randomized controlled trials (RCTs) and observational studies comparing seizure events or seizure-related outcomes between one brand-name AED and at least one alternative version produced by a distinct manufacturer. We identified 16 articles (9 RCTs, 1 prospective nonrandomized trial, 6 observational studies). We assessed characteristics of the studies and, for RCTs, extracted counts for patients whose seizures were characterized as 'controlled' and 'uncontrolled'. Seven RCTs were included in the meta-analysis. The aggregate odds ratio (n = 204) was 1.1 (95% CI 0.9, 1.2), indicating no difference in the odds of uncontrolled seizure for patients on generic medications compared with patients on brand-name medications. In contrast, the observational studies identified trends in drug or health services utilization that the authors attributed to changes in seizure control. Although most RCTs were short-term evaluations, the available evidence does not suggest an association between loss of seizure control and generic substitution of at least three types of AEDs. The observational study data may be explained by factors such as undue concern from patients or physicians about the effectiveness of generic AEDs after a recent switch. In the absence of better data, physicians may want to consider more intensive monitoring of high-risk patients taking AEDs when any switch occurs.

Prescribing generic antiepileptic drugs: Issues and concerns for nurse practitioners

PURPOSE

To educate prescribing clinicians about bioequivalent standards for therapeutic equivalence of brand and generic antiepileptic drugs (AEDs) as more generic drugs come to market, and to increase awareness of practice and safety issues surrounding the use of these drugs for people with seizures.

DATA SOURCES

Information was gathered from a search of the scientific literature as well as the author's clinical experience.

CONCLUSIONS

Controversy exists regarding the therapeutic equivalence of brand and generic AEDs, even when bioequivalent standards are satisfied. Generic AEDs have been associated with breakthrough seizures and adverse events that may outweigh cost savings encouraged by third-party payors. Further research is needed comparing brand to generic drugs in a rigorous manner in order to make a consensus statement regarding the safety and equivalency of generic AEDs for all patient populations.

IMPLICATIONS FOR PRACTICE

Generic AEDs may be safely prescribed in certain situations if clinicians are aware of ethical, legal, and practice issues surrounding their use. Sufficient time should be spent educating patients, caregivers, and pharmacists about implications of a switch made without the knowledge of the patient and/or prescriber.

The Controversy over Generic Antiepileptic Drugs

As patent protection ends for the next generation of antiepileptic drugs (AEDs), a complex debate continues over generic substitution of AEDs. On one hand, generic drug formulations provide cost savings for patients and society. On the other hand, patients with epilepsy and physicians are wary about the adequacy and efficacy of the Food and Drug Administration's (FDA) standards for generics. This article reviews current and proposed bioequivalence test procedures, summarizes new generic AED formulations and their costs, and discusses potential pitfalls in the current standards. These shortcomings include certain pharmacokinetic factors and clinical pharmacologic factors that may affect bioequivalence of generic AEDs, and statistical limitations of the standards. While the drug concentration differences between the brand name drug and each generic formulation are unlikely to be substantial, the differences with generic-to-generic switches will be greater and potentially clinically significant. Conversely, owing to their more favorable pharmacokinetic profile, newer AEDs may be less prone to problems with generic substitution than older ones. Unfortunately, very few data are available to guide decisions regarding what is best for an individual patient. Based on new prediction methods, generic substitution should be safe for many patients but identifying them ultimately requires more rigorous study.

Understanding therapeutic equivalence in epilepsy

The issues surrounding generic drug substitution in patients with epilepsy are complex. The substitution of one formulation of an antiepileptic drug (AED) for another is controversial. Well-reasoned and defensible cases can be made both for and against such substitution. Although regulatory agencies require that generic and proprietary drugs have similar pharmacokinetic bioequivalence data, their therapeutic efficacy may not necessarily be identical. The paroxysmal nature of epilepsy, the narrow therapeutic index of some AEDs, the need to individualize therapy to achieve seizure control, and the negative consequences of uncontrolled epilepsy distinguishes epilepsy from other clinical conditions. Epilepsy management with AEDs requires careful dose titration and consistent drug exposure at the optimal level for each patient, which can be altered if a different formulation of the AED is substituted. Unexpected variability in plasma concentrations could occur when a patient who has been receiving one formulation of an AED (generic or brand) receives an alternate formulation. Thus, no substitutions should be made for people with epilepsy without the knowledge and approval of the prescribing physician. Patients should be consulted about the substitution, with all risks and benefits carefully explained.

Association between antiepileptic drug switching and epilepsy-related events

Switching between bioequivalent antiepileptic drugs (AEDs) in patients with epilepsy remains a concern because of possible untoward effects owing to a narrow therapeutic range. We investigated the association between switching A-rated AEDs and epilepsy-related events. We conducted a case-control study using claims from the MarketScan database. Cases were defined by an emergently treated epilepsy-related event with the primary diagnosis of epilepsy. Controls had an epilepsy outpatient office visit. Eighty-four of 757 (11.1%) cases and 147 of 2271 (6.5%) controls experienced an A-rated switch. The odds of an epilepsy-related event were 1.78-fold higher for switchers (95% CI 1.35 to 2.36) and, when adjusted for gender and total number of AED prescriptions filled, 1.57-fold higher (95% CI=1.17-2.10). Switching between A-rated formulations of AEDs is associated with an increased risk of emergently treated epilepsy-related events. These findings suggest that care should be taken when considering a switch between A-rated AEDs in patients with epilepsy.

Substitution of anticonvulsant drugs

Changing from branded drugs to generic alternatives, or between different generic formulations, is common practice aiming at reducing health care costs. It has been suggested that antiepileptic drugs (AEDs) should be exempt from substitution because of the potential negative consequences of adverse events and breakthrough seizures. Controlled data are lacking on the risk of substitution. However, retrospective data from large medical claims databases suggest that switching might be associated with increased use of AED and non-AED medications, and health care resources (including hospitalization). In addition, some anecdotal evidence from patients and health care providers' surveys suggest a potentially negative impact of substitution. Well-controlled data are needed to assess the real risk associated with substitution, allowing health care professionals involved in the care of patients with epilepsy to make informed decisions. This paper reviews currently available literature, based on which the authors suggest that the decision to substitute should be made on an individual basis by the physician and an informed patient. Unendorsed or undisclosed substitution at the pharmacy level should be discouraged.

Case-control analysis of ambulance, emergency room, or inpatient hospital events for epilepsy and antiepileptic drug formulation changes

PURPOSE

Although antiepileptic drugs (AEDs) with multisource generic alternatives are becoming more prevalent, no case-control studies have been published examining multisource medication use and epilepsy-related outcomes. This study evaluated the association between inpatient/emergency epilepsy care and the occurrence of a recent switch in AED formulation.

METHODS

A case-control analysis was conducted utilizing the Ingenix LabRx Database. Eligible patients were 12-64 years of age, received >or=145 days of AEDs in the preindex period, had continuous eligibility for 6 months preindex, and no prior inpatient/emergency care. Cases received care between 7/1/2006 and 12/31/2006 in an ambulance, emergency room, or inpatient hospital with a primary epilepsy diagnosis. Controls had a primary epilepsy diagnosis in a physician's office during the same period. The index date was the earliest occurrence of care in each respective setting. Cases and controls were matched 1:3 by epilepsy diagnosis and age. Odds of a switch between "A-rated" AEDs within 6 months prior to index were calculated.

RESULTS

Cases (n = 416) had 81% greater odds of having had an A-rated AED formulation switch [odds ratio (OR) = 1.81; 95% confidence interval (CI) = 1.25 to 2.63] relative to controls (n = 1248). There were no significant differences between groups regarding demographics or diagnosis. Significant differences were found with regard to medical coverage type (case Medicaid = 4.6%, control Medicaid = 1.8%, p = 0.002). Post hoc analysis results excluding Medicaid recipients remained significant and concordant with the original analysis.

DISCUSSION

This analysis found an association between patients receiving epilepsy care in an emergency or inpatient setting and the recent occurrence of AED formulation switching involving A-rated generics.

Generic products of antiepileptic drugs (AEDs): is it an issue?

The availability of generic products of antiepileptic drugs (AEDs) has raised the following concerns: (1) Do generic AEDs work as well as brand AEDs in terms of their efficacy, safety and quality? (2) Can generic AEDs be used as substitutions for brand AEDs? and (3) Can generic products of AEDs be used interchangeably? The traditional average bioequivalence analysis addresses concern 1 but does not provide a complete adequate response to concerns 2 and 3. Drug interchangeability can be classified as drug prescribability or drug switchability. Drug prescribability refers to the situation where a patient is treated for the first time so that either a brand or a bioequivalent generic AED can be chosen. Drug switchability refers to the situation in which a brand AED is switched to a bioequivalent generic product of the same AED. The traditional average bioequivalence approach is sufficient to evaluate the prescribability of generic products, but does not ensure the switchability between prescribable formulations. The necessity of assuring switchability of two formulations can be addressed by individual bioequivalence. While the switch to generic AEDs is well tolerated by many patients and in general cost-effective, seizure control should not be sacrificed on the basis of cost alone, as the major end point in treating epilepsy with AEDs is seizure control without side effects. Until we have individual (within patient) bioequivalence data on generic AEDs and/or the tools to a priori identify the subset of patients susceptible to the generic switch, a switch of AED products in seizure-free patients is not recommended.