Comparison of steady-state blood levels of two carbamazepine formulations

Ionic Liquids: New Forms of Active Pharmaceutical Ingredients with Unique, Tunable Properties

This Review aims to summarize advances over the last 15 years in the development of active pharmaceutical ingredient ionic liquids (API-ILs), which make up a prospective game-changing strategy to overcome multiple problems with conventional solid-state drugs, for example, polymorphism. A critical part of the present Review is the collection of API-ILs and deep eutectic solvents (DESs) prepared to date. The Review covers rules for rational design of API-ILs and tools for API-IL formation, syntheses, and characterization. Nomenclature and ionic speciation, and the confusion that these may cause, are highlighted, particularly for speciation in both ILs and DESs of intermediate ionicity. We also highlight in vivo and in vitro pharmaceutical activity studies, with differences in pharmacokinetic/pharmacodynamic depending on ionicity of API-ILs. A brief overview is provided for the ILs used to deliver drugs, and the Review concludes with key prospects and roadblocks in translating API-ILs into pharmaceutical manufacturing.

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.

Polymorph Impact on the Bioavailability and Stability of Poorly Soluble Drugs

Drugs with low water solubility are predisposed to poor and variable oral bioavailability and, therefore, to variability in clinical response, that might be overcome through an appropriate formulation of the drug. Polymorphs (anhydrous and solvate/hydrate forms) may resolve these bioavailability problems, but they can be a challenge to ensure physicochemical stability for the entire shelf life of the drug product. Since clinical failures of polymorph drugs have not been uncommon, and some of them have been entirely unexpected, the Food and Drug Administration (FDA) and the International Conference on Harmonization (ICH) has required preliminary and exhaustive screening studies to identify and characterize all the polymorph crystal forms for each drug. In the past, the polymorphism of many drugs was detected fortuitously or through manual time consuming methods; today, drug crystal engineering, in particular, combinatorial chemistry and high-throughput screening, makes it possible to easily and exhaustively identify stable polymorphic and/or hydrate/dehydrate forms of poorly soluble drugs, in order to overcome bioavailability related problems or clinical failures. This review describes the concepts involved, provides examples of drugs characterized by poor solubility for which polymorphism has proven important, outlines the state-of-the-art technologies and discusses the pertinent regulations.

Rational use of generic psychotropic drugs

For economic reasons, the generic substitution of branded medications is common and welcome. These replacements are based on the concept of bioequivalence, which is considered equal to therapeutic equivalence. Regulatory standards for bioequivalence require the 90 % confidence intervals of group averages of pharmacokinetic measures of a generic and the original drug to overlap within ±20 %. However, therapeutic equivalence has been challenged for several psychotropic agents by retrospective studies and case reports. To evaluate the degree of bioequivalence and therapeutic equivalence of branded and generic psychotropic drugs, we performed an electronic search (from database inception until 24 May 2012 and without language restrictions) in PubMed/MEDLINE, Cochrane Library, and Web of Science. Search terms were "(generic) AND (psychotropic OR psychoactive OR antipsychotic OR antiepileptic OR antidepressant OR stimulant OR benzodiazepine)" or the respective individual substances. We included clinical studies, regardless of design, comparing branded with generic psychotropic drug formulations, identifying 35 such studies. We also included case reports/series reporting on outcomes after a switch between brand and generic psychotropics, identifying 145 clinical cases. Bioequivalence studies in healthy controls or animals, in-vitro studies, and health economics studies without medical information were excluded. An overview of the few randomized controlled studies supports that US FDA regulations assure clinically adequate drug delivery in the majority of patients switched from brand to generic. However, with a growing number of competing generic products for one substance, and growing economic pressure to substitute with the currently cheapest generic, frequent generic-generic switches, often unbeknownst to prescribing clinicians, raise concerns, particularly for antiepileptics/mood stabilizers. Generic-generic switches may vary by more than ±20 % from each other in individual patients since the pharmacokinetic properties of each generic may differ from the innovator drug in opposing directions. Ideally, therapeutic equivalence studies in addition to pharmacokinetic equivalence studies would be performed for each generic, reflecting the full variability of clinical responses due to changes of pharmacokinetic properties related to age, sex, ethnicity, genetic factors, and body mass index. This is particularly relevant, as bioequivalence studies are based on single-dose studies in healthy controls who are likely not representative of the patients who are prescribed the psychotropic medications. Additionally, individual case reports suggest potential clinical effects during brand-generic switches. Knowledge and consideration of intra-individual variations can help guide the clinical management during brand-generic or generic-generic switch periods. To optimize outcomes, clinicians need to consider that when using generic psychotropic medications, a change in the patient's clinical status can be related to psychological, interactional, physiological, and pharmacological factors that may or may not be related to the change to a generic drug. In addition, throughout all treatment periods, clinicians need to be aware of the currently dispensed product (i.e., branded or exact generic formulation), particularly when evaluating clinical changes in efficacy, tolerability, and adherence. If clinical problems occur, the first response should be an assessment of adherence and a careful dose adjustments of the generic drug rather than an immediate switch back to the originator.

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.

Efficacy and safety of innovator versus generic drugs in patients with epilepsy: a systematic review

Generic antiepileptic drugs achieve blood concentrations similar to those of innovator drugs in healthy volunteers, but their comparative effectiveness has not been well evaluated. Thus, we assessed the efficacy, tolerability, and safety of innovator versus generic antiepileptic drugs. We searched the MEDLINE database, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and Web of Science for studies that evaluated innovator and generic antiepileptic drugs in patients with epilepsy and reported data on prespecified outcomes. We extracted data on study design, interventions, quality criteria, study population, baseline characteristics, and outcomes. Compared with initiation of innovator antiepileptic drugs, initiation of generic antiepileptic drugs did not significantly alter seizure occurrence (relative risk [RR] 0.87, 95% confidence interval [CI] 0.64-1.18; strength of evidence: low) or frequency (standardized mean difference 0.03, 95% CI -0.08-0.14; strength of evidence: low), withdrawals due to lack of efficacy (RR 1.02, 95% CI 0.41-2.54; strength of evidence: low) or adverse events (RR 0.79, 95% CI 0.28-2.20; strength of evidence: low), pharmacokinetic concentrations (maximum, minimum, or area under the curve [strength of evidence: low]), or a myriad of adverse events (strength of evidence: low or insufficient) in clinical trials. In qualitatively evaluated observational studies, switching between forms of antiepileptic drug (innovator to generic, generic to generic) may increase the risk of hospitalization (strength of evidence: low), hospital stay duration (strength of evidence: low), and a composite end point of medical service utilization (strength of evidence: insufficient) but may not increase outpatient service utilization (strength of evidence: low). Data are limited predominantly to carbamazepine, phenytoin, and valproic acid. Clinical trials are limited by small sample size, short-term nature, and lack of specification of A-rated generic products (generics that the United States Food and Drug Administration has deemed bioequivalent to the innovator drug). Observational trials lack full accounting for confounders and have inherent limitations. With a low strength of evidence, it appears that initiating an innovator or generic antiepileptic drug will provide similar efficacy, tolerability, and safety but that switching from one form to the other may be associated with more hospitalizations and longer hospital stays.

Generic Substitution of Antiepileptic Drugs: A Systematic Review of Prospective and Retrospective Studies

Objective:

To systematically review the literature on generic antiepileptic drugs (AEDs), evaluate the efficacy and safety of generic AED substitution, and perform pharmacokinetic (PK) analysis using the American Academy of Neurology (AAN) scheme to classify evidence.

Data Sources:

PubMed and Cumulative Index to Nursing and Allied Health Literature searches from January 1, 1980, to October 15, 2010, were performed using the search terms anticonvulsant, antiepileptic drug, carbamazepine, divalproex, ethosuximide, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, phénobarbital, Phenytoin, primidone, topiramate, valproate, valproic acid, and zonisamide; bioavailability, bioequivalence, bioequivalency, bioequivalent, and substitution; and generic.

Study Selection and Data Extraction:

Retrospective and prospective controlled studies of generic substitution of AEDs were included in the review. Non-English-language articles and uncontrolled clinical studies were excluded, Published articles were categorized using the AAN criteria for systematic reviews.

Data Synthesis:

We identified 156 articles. Of these, 20 met our inclusion criteria; 7 were retrospective studies, 6 were prospective studies in patients with epilepsy, and 7 were prospective studies in healthy subjects. All articles were rated Class I to Class III, using AAN criteria. The retrospective studies were categorized as Class III and showed a significant relationship between generic substitution and increased use of health care resources because of seizures or AED toxicity. Prospective studies were categorized as Class I, II, and III. Prospective studies in patients showed no differences between brand and generic drugs in PK parameters of bioequivalence. Three prospective studies in healthy subjects reported significant differences in maximum drug concentrations. Comparison of brand and generic drugs revealed no significant difference in seizure frequency; however, some prospective studies showed significant differences in PK parameters, primarily those not used for bioequivalence determinations.

Conclusions:

There is inconsistency between retrospective and prospective studies of generic AED substitution. The highest levels of evidence indicate that there should not be a problem with generic substitution, although some patients are more prone to problems with the generic products. Some evidence suggests that switches between multiple generic AED products in certain individuals may be problematic.

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.

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.

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.

Incidence of postoperative infections in patients undergoing coronary artery bypass grafting surgery receiving antimicrobial prophylaxis with original and generic cefuroxime

OBJECTIVE

The aim of this study was to compare the incidence of post-operative infections in patients undergoing coronary artery bypass grafting (CABG) surgery who received generic cefuroxime (gCFX) instead of original cefuroxime (oCFX) as antimicrobial prophylaxis.

METHODS

The study had two parts, a prospective and a retrospective one (4 weeks with oCFX followed by 4 weeks with gCFX in each part; total study duration of 16 weeks). The studied patient population was 618 consecutive adult patients who underwent on pump CABG surgery. Patients were divided into two groups according to type of formulation they received: 313 patients received oCFX and 305 gCFX.

RESULTS

Eight (2.5%) and 39 (12.8%) patients in the oCFX and gCFX group, respectively, developed postoperative infections (p<0.001). There were 6 (1.9%) surgical site infections in the oCFX group and 31 (10.1%) in the gCFX group (p<0.001). Bacteremia occurred in 2 (0.6%) patients in the oCFX group and in 8 (2.6%) patients in the gCFX group (p=0.1). In addition, septic shock occurred in 6 cases (2.0%, p=0.04) and multiple organ failure in another 4 patients (1.3%, p=0.1) in the gCFX group. The most common pathogens isolated were Gram-positive cocci in both groups.

CONCLUSIONS

This study revealed a higher incidence of postoperative infections in adult patients undergoing CABG surgery receiving gCFX compared to oCFX as antimicrobial prophylaxis. The findings of our study provide additional evidence regarding the problem of substandard drugs, in our case a formulation of a generic antibiotic, even in developed countries. ULTRAMINI-SUMMARY: The incidence of post-operative infections following CABG surgery was higher in adult patients receiving generic instead of original cefuroxime as antimicrobial prophylaxis. The findings of our study provide additional evidence regarding the problem of substandard drugs, in our case a formulation of a generic antibiotic, even in developed countries.

Current approaches to the use of generic antiepileptic drugs

Generic substitution is encouraged as a cost containment strategy for the management of health care resources. However, in epilepsy, the consequences of loss of symptom control are important, and antiepileptic drugs have narrow therapeutic indices. For this reason, generic substitution may be problematic, and certain health authorities have excluded antiepileptic drugs from overall policy recommendations on generic prescribing. The absence of bioequivalence data among generic forms and the relatively broad criteria for bioequivalence with the branded drug allow differences in drug exposure to arise that may be clinically relevant and necessitate monitoring of plasma levels when switching formulations to avoid loss of seizure control or emergence of side effects. Management of these issues carries a significant cost, which should be weighed carefully against the cost savings acquired when purchasing the drug. Both physicians and patients have a right to be informed and approve before pharmacists make a generic substitution or switch between generics.

Recommendations of the Italian League Against Epilepsy Working Group on Generic Products of Antiepileptic Drugs

The availability of generic products of antiepileptic drugs (AEDs) has been increasing in recent years. In view of the importance of the issue, the Italian League against Epilepsy (LICE) set up an ad hoc working group whose task was to assess available evidence on the efficacy and safety of generic AEDs in the treatment of epilepsy and to produce recommendations on their use. A careful review of the literature revealed no adequately powered randomized controlled trials that assessed the risk/benefit ratio of generic substitution. Although there have been reports of loss or worsened seizure control, or appearance of adverse events, following the switch from brand products to generics, a critical assessment of the evidence generally does not allow us to establish a cause-effect relationship between the switch and a change in clinical status. Overall, the working group concluded that generic AEDs meeting current regulatory criteria for bioequivalence represent a valuable choice in the management of epilepsy by allowing a substantial reduction of treatment costs, particularly in patients initiating monotherapy or adjunctive treatment and in those with persistent seizures. The working group considered that in patients who achieved seizure freedom a modest change in plasma drug levels, which may occasionally occur even after substitution of products that meet bioequivalence criteria, could in rare cases lead to seizure breakthrough. Therefore, generic substitution is not recommended in patients who achieved seizure remission. Switches between a particular generic and another generic should also be preferably avoided. Finally, sustained-release AED formulations should not be used interchangeably with immediate-release brand or generic products. Patients need to be informed about the stringent criteria that currently govern the approval of generic products and about the implications of the use of generic AEDs, and their opinion should be taken into consideration at the time of prescribing.

Are there potential problems with generic substitution of antiepileptic drugs?

In response to increasing cost pressures, healthcare systems are encouraging the use of generic medicines. This review explores potential problems with generic substitution of antiepileptic drugs (AEDs). A broad search strategy identified approximately 70 relevant articles. Potential problems with generic substitution included: The limited evidence (mainly case reports with some pharmacokinetic studies) appears to support these concerns for older AEDs. As a result, restrictions on use of specific generic AEDs are in place in some countries and recommended by some lay epilepsy organisations. As more AEDs lose patent protection, it is important to examine the question of whether generic substitution may pose problems for patients with epilepsy, and whether there should be safeguards to ensure that both physician and patient are informed when generic substitution occurs.

Physicians underestimate the frequency of generic carbamazepine substitution: results of a survey and review of the problem

Antiepileptic drugs (AEDs) possess a narrow therapeutic range, and generic substitution may lead to breakthrough seizures and adverse events. Prescribers of AEDs may be unaware how frequently generic substitution actually occurs. Surveys were administered to 845 physicians at the 2001 American Epilepsy Society (AES) meeting and the 2001 American Academy of Neurology (AAN) meeting. Two hundred fifty-eight physicians responded to the AES survey and 587 physicians to the AAN survey. Questions were multiple choice and displayed on a computer screen. Among other questions, physicians were asked: (1) What percentage of patients are substituted with a generic short-acting carbamazepine in the US annually? (2) Are you comfortable with patients receiving multiple formulations of generic carbamazepine? Responses to the first question were compared to the actual rate of generic substitution determined by an independent audit of 1,036,000 Tegretol prescriptions. In the AES survey, 10.9% of respondents estimated that 10% of patients had carbamazepine generic substitutions, 41.9% estimated a 30% substitution rate, 30.2% estimated a 50% rate, and 17.1% estimated a 70% rate. The AAN respondents had similar estimates: 17.5% guessed a 10% rate, 40.0% a 30% rate, 30.2% a 50% rate, and 12.3% a 70% rate. In the AES survey, 86.4% of respondents were not "comfortable with patients receiving multiple formulations of generic carbamazepine." Similarly, in the AAN survey, 80.3% of respondents did not endorse generic substitution of carbamazepine. An independent audit of generic substitutions revealed that of 766,000 prescriptions for 200mg of Tegretol, pharmacists substituted 551,000 (72%) with generic carbamazepine. Of 199,000 prescriptions for 100mg of Tegretol, 140,000 (70%) were filled with a generic. Of 71,000 prescriptions for Tegretol 100mg/5ml suspension, 10,000 (14%) were filled with a generic. The overall substitution rate was 701,000/1,036,000 (68%), much higher than estimated by the majority of surveyed attendees. In conclusion, most surveyed physicians at the 2001 AES and AAN meetings significantly underestimated the number of generic substitutions that occur for brand name short-acting carbamazepine. Given the potential for breakthrough seizures and adverse events related to generic substitution, physicians need to be more vigilant in their prescription-writing practices to prevent unwarranted generic substitution.

Generic substitution for brand name antiepileptic drugs: a survey

BACKGROUND/OBJECTIVE

There are presently 26 different generic preparations for five brand name antiepileptic drugs (AEDs) on the Canadian market with others likely to be released in the near future. The purpose of this review is to examine the basis for the controversy surrounding generic substitution for brand name antiepileptic drugs, to present the results of a survey of neurologists' and patients' attitudes toward generic substitution and to increase neurologists' awareness of the issues.

METHODS

The current federal and provincial regulations pertaining to generic drug approval and substitution are reviewed. Published anecdotal and survey reports of the effectiveness and tolerability of generic substitution for AEDs are reviewed. A pilot questionnaire survey of 83 patients from four adult epilepsy clinics and 46 neurologists from across Canada was undertaken to determine attitudes toward generic substitution.

RESULTS AND CONCLUSIONS

Several authors have suggested that some AEDs, particularly those with a narrow therapeutic index, may pose problems with generic substitution. Although generic AEDs are lower in price, possible increased side effects and morbidity and the need for closer monitoring could partially offset the cost savings. The results of our survey highlight significant unawareness of the process of generic substitution among both patients and neurologists and reveal a general level of discomfort among neurologists to prescribe generic AEDs. Further data should be obtained about the potential consequences of generic substitution in epilepsy patients.

Comparative study of bioavailability and clinical efficacy of carbamazepine in epileptic patients

OBJECTIVE

To compare the bioavailability of three generic brands of carbamazepine tablets with that of a proprietary brand in adult patients with epilepsy.

DESIGN

A double-blind, randomized, three-phase crossover study.

SETTING

A psychiatric facility.

PARTICIPANTS

Eighteen patients with epilepsy who had taken carbamazepine at least 5 months before entering the study.

MAIN OUTCOME MEASURES

Ten blood specimens from each patient were collected at steady-state. Plasma concentration of carbamazepine was analyzed for pharmacokinetic parameters such as maximum plasma concentration (Cmax), mean time to reach maximum concentration (tmax), and mean AUC.

RESULTS

There were no statistically significant differences in these parameters among four brands of carbamazepine. However, when comparing the 90% CI of AUC of three generic brands with that of the proprietary brand, the AUC of two generic brands lay within a range of 80% to 120%. The effects of gender and each brand of carbamazepine on these pharmacokinetic parameters were also analyzed. Breakthrough seizures occurred even though the plasma concentration of carbamazepine was therapeutic.

CONCLUSIONS

The bioavailability of two generic brands of carbamazepine tablets (Carmapine and Carzepine) and the proprietary brand (Tegretol) were equivalent in this sample of adult patients with epilepsy.

Generic prescribing for epilepsy. Is it safe?

Generic prescribing for epilepsy remains controversial. This study aimed to ascertain if a change occurred in the incidence of seizures or side-effects when a different pharmaceutical manufacturer's version of the same antiepileptic drug was taken (a 'switch'). Forty general practices with a list size of 350 168 were recruited. They identified 2285 people being treated for epilepsy with either carbamazepine, phenytoin or sodium valproate. A questionnaire was sent to the people with epilepsy. Those who recalled taking a different pharmaceutical manufacturer's supply of the same antiepileptic drug over the last 2 years were interviewed by their practice if they reported a problem with the control of their epilepsy after a 'switch'. One thousand, three hundred and thirty-three (58.8%) people with epilepsy responded: 251 (18.7%) had experienced a 'switch', 27 (10.8%) reported 'validated' problems; 25 (9.9%) reported unproven problems; 22 (8.8%) reported problems, but follow-up was incomplete; 177 (70.5%) reported no problems. This study suggests that money saved by generic prescribing is outweighed by negative health gain for the person with epilepsy, increased work in general practice, and increased social costs.

Comparative bioavailability of a generic phenytoin and Dilantin

Generic substitution of antiepileptic drugs (AEDs) has been controversial, with many alleged instances of biologic and therapeutic inequivalence reported. The recall of a generic phenytoin (PHT) formulation used in the Veterans Administration (VA) medical system allowed us to evaluate the question of biologic equivalence systematically in a relatively large number of patients at the Bronx VA Medical Center. Serum PHT levels were 22-31% lower during the period of generic intake as compared with levels in the same patients receiving Dilantin. Review of the literature showed only one other adequately documented report of potential clinically significant inequivalence between a brand name and generic AED. Despite the apparent infrequency of generic inequivalence, several areas in which procedures for certification of therapeutic equivalence should be improved were identified.

The bioinequivalence of carbamazepine tablets with a history of clinical failures

The bioavailability of three lots of a generic 200-mg carbamazepine tablet, which had been withdrawn from the market, was compared to the bioavailability of one lot of the innovator product in 24 healthy volunteers. Fifty-three lots of the generic product had been recalled by the manufacturer because of concerns over reports of clinical failures for several of the lots. The three generic lots tested in this study exhibited a wide range of bioavailability, as well as large differences in the in vitro dissolution rates. The mean maximum carbamazepine plasma concentrations for two of the generic lots were only 61-74% that of the innovator product, while the third lot was 142% of the innovator. The mean areas under the plasma concentration-time curve for the three generic lots ranged from 60 to 113% that of the innovator product. The results clearly indicate a significant difference in the rate and extent of absorption of the generic products compared to the innovator, as well as among the generic lots. A good relationship was found between the in vivo parameters and the in vitro dissolution results for the four dosage forms.

Loss of seizure control associated with generic substitution of carbamazepine

OBJECTIVE

We report two cases of lost seizure control associated with the generic substitution of carbamazepine, review pertinent literature, and discuss the impact of this substitution on patient care.

DATA SOURCES

Case studies, abstracts, and research publications identified in MEDLINE and bibliographic review.

DATA EXTRACTION

One author reviewed cases supplied by the other authors and abstracted information from published literature sources.

DATA SYNTHESIS

The first case describes a 15-year-old boy who received valproic acid and carbamazepine for partial seizures. A change in government program policies caused him to receive generic carbamazepine. This resulted in loss of seizure control and a decrease in his serum carbamazepine concentration from 12.4 to 6.7 micrograms/mL. When his carbamazepine concentration returned to previous levels, seizure control was not reestablished. A second case involves a 21-year-old woman who substituted generic carbamazepine because of financial problems. After being seizure-free for at least five years on phenobarbital and carbamazepine, she experienced seizures related to the product change. Her carbamazepine concentration decreased from 11.8 to 8.5 micrograms/mL; she also became pregnant at that time. Seizure control was not reestablished. At least three other studies do not support these observations, but the tightly controlled conditions in these studies may not have simulated actual clinical practice.

CONCLUSIONS

When generic substitution of carbamazepine is required, serum concentrations should be carefully monitored. The extra care required may negate the financial advantages of the substitution.