Steady-state carbamazepine pharmacokinetics following oral and stable-labeled intravenous administration in epilepsy patients: effects of race and sex

Carbamazepine is a widely prescribed antiepileptic drug. Owing to the lack of an intravenous formulation, its absolute bioavailability, absolute clearance, and half-life in patients at steady state have not been determined. We developed an intravenous, stable-labeled (SL) formulation in order to characterize carbamazepine pharmacokinetics in patients. Ninety-two patients received a 100-mg infusion of SL-carbamazepine as part of their morning dose. Blood samples were collected up to 96 hours after drug administration. Plasma drug concentrations were measured with liquid chromatography-mass spectrometry, and concentration-time data were analyzed using a noncompartmental approach. Absolute clearance (l/hr/kg) was significantly lower in men (0.039 ± 0.017) than in women (0.049 ± 0.018; P = 0.007) and in African Americans (0.039 ± 0.017) when compared with Caucasians (0.048 ± 0.018; P = 0.019). Half-life was significantly longer in men than in women as well as in African Americans as compared with Caucasians. The absolute bioavailability was 0.78. Sex and racial differences in clearance may contribute to variable dosing requirements and clinical response.

Zonisamide discontinuation due to psychiatric and cognitive adverse events: a case-control study

OBJECTIVES

Zonisamide (ZNS) is an antiepileptic drug (AED) that has been associated with psychiatric adverse events (PAE) and cognitive adverse events (CAE); controlled studies evaluating these adverse events are limited. Our objectives were to 1) determine the incidence of PAE and CAE leading to the discontinuation of ZNS and 2) identify risk factors for PAE and CAE associated with the discontinuation of ZNS.

METHODS

All patients exposed to ZNS at MINCEP Epilepsy Care between March 2000 and September 2008 were identified. Reasons for discontinuing ZNS were documented. Separate case-control studies were performed to identify risk factors associated with the discontinuation of ZNS due to PAE or CAE via multivariate binary logistic regression.

RESULTS

A total of 544 patients were exposed to ZNS during the study period. PAE and CAE were the most frequently identified reasons for terminating ZNS therapy. The incidence of PAE severe enough to be associated with the discontinuation of ZNS was 6.9%; the incidence of CAE was 5.8%. Factors associated with termination of ZNS therapy due to PAE were past psychiatric history (p = 0.005), symptomatic generalized epilepsy (p = 0.027), and lower maximum ZNS serum concentration (mean = 17.9 mg/L vs 34.7 mg/L, p < 0.001). Independent variables associated with discontinuing ZNS due to CAE were greater number of concomitant AEDs (p = 0.011) and lower maximum ZNS serum concentration (mean = 16.6 mg/L vs 30.6 mg/L, p = 0.002).

CONCLUSIONS

We have identified clinically relevant risk factors associated with the discontinuation of ZNS. Our findings support the concept that selected patients are relatively more vulnerable to CNS adverse events when exposed to ZNS.

Lower phenytoin serum levels in persons switched from brand to generic phenytoin

After generic phenytoin (PHT) was marketed, the authors identified eight adult patients (ages 34 to 49) whose seizures increased enough to require intervention after switching to generic PHT. The mean total PHT concentration on brand (before generic) was 17.7 +/- 5.3 mg/L, decreased to 12.5 +/- 2.7 mg/L with generic, and increased to 17.8 +/- 3.9 mg/L after brand was re-introduced. Brand and generic PHT do not yield equivalent concentrations in some patients and substitution should not be permitted without physician notification.

Discontinuation of levetiracetam because of behavioral side effects: A case-control study

BACKGROUND

Levetiracetam (LEV) is a recently approved anticonvulsant with proven efficacy and safety in the treatment of partial seizures. LEV may cause behavioral abnormalities that can be severe and require discontinuation of this drug. Risk factors for discontinuing LEV have not been established.

OBJECTIVE

To determine incidence of behavioral abnormalities severe enough to require discontinuation of LEV and identify risk factors for such behavioral abnormalities.

METHODS

All patients treated with LEV at MINCEP between January 2000 and February 2002 constituted the study population (n = 553). Patients who had discontinued LEV for behavioral reasons were selected as index cases. Case controls were patients starting LEV immediately after the index case. Potential risk factors for LEV discontinuation included age, gender, cognitive function, history of psychiatric diagnosis, epilepsy syndrome, number of antiepileptic drugs, titration rate, maximum dose of LEV, and LEV level at maximum dose.

RESULTS

Thirty-eight patients (6.9%) discontinued LEV because of behavioral abnormalities. Variables associated with LEV discontinuation included faster titration rate to maximal dose, history of a psychiatric disorder, and diagnosis of symptomatic generalized epilepsy. Patients who discontinued LEV owing to behavioral reasons had significantly lower maximum LEV doses than controls.

CONCLUSIONS

This study identified variables associated with discontinuation of LEV due to behavioral abnormalities. Slower titration of LEV should be considered in those patients at higher risk of discontinuing LEV for behavioral reasons.

Variability of total phenytoin serum concentrations within elderly nursing home residents

BACKGROUND

Approximately 6% of all elderly nursing home residents receive phenytoin. Phenytoin concentrations are often measured to guide therapy.

OBJECTIVE

To evaluate the intraresident variability among multiple measurements of total phenytoin serum concentrations in nursing home residents.

METHODS

This was an observational study of 56 elderly (>or=65 years) nursing home residents from 32 nursing homes who had at least 3 phenytoin concentrations measured while on the same dose of phenytoin for at least 4 weeks and who were not taking any interfering concomitant medications. These were a subset of 387 elderly nursing home residents from 112 nursing homes across the United States who had total phenytoin concentration measurements between June 1998 and December 2000.

RESULTS

The mean age was 80.1 years (range, 65 to 100 years) and 58.9% were women. The mean daily dose of phenytoin per resident was 4.9 +/- 1.5 mg/kg. Total phenytoin concentrations within an elderly nursing home resident varied as much as two- to threefold, even though there was no change in dose. The person with the smallest variability had a minimum concentration of 10.0 micro g/mL and a maximum of 10.4 micro g/mL. The person with the largest variability had a minimum concentration of 9.7 micro g/mL and a maximum of 28.8 micro g/mL.

CONCLUSIONS

There is considerable variability in the total phenytoin concentrations in the elderly nursing home resident and measurement of a single total phenytoin concentration should not be used to guide treatment.

A double-blind, placebo-controlled study of remacemide hydrochloride in patients with refractory epilepsy following pre-surgical assessment

This multicentre, randomised, double-blind, placebo-controlled, parallel-group study investigated the efficacy, safety and pharmacokinetics of remacemide hydrochloride in adult patients ( n= 59) with refractory epilepsy, undergoing reduced or discontinued antiepileptic drug (AED) usage, as part of an evaluation for epilepsy surgery. On discontinuation or reduction of maintenance AEDs, patients received remacemide hydrochloride, up to 600 mg daily, or placebo, for up to ten days or until they experienced a fourth complex partial (CPS) or a generalised tonic-clonic (GTC) seizure. Pre- and post-study blood and urine samples were taken for analysis. Remacemide hydrochloride showed a significantly ( P= 0.045) longer median time to fourth seizure compared with placebo (6.8 vs. 3.8 days). Median nine-day seizure counts were significantly ( P= 0.0327) lower with remacemide hydrochloride than placebo (6.2 vs. 12.8). Eleven remacemide hydrochloride patients and six placebo patients completed ten days' treatment. Remacemide and desglycinyl metabolite levels were lower in patients receiving concomitant carbamazepine or phenytoin than in those receiving non-inducing AEDs or remacemide hydrochloride alone. No serious adverse events occurred; all patients receiving remacemide hydrochloride completed the study. Remacemide hydrochloride was well tolerated and showed significant therapeutic activity in this patient population.

Lamotrigine clearance during pregnancy

OBJECTIVE

To evaluate changes in lamotrigine (LTG) clearance before, during, and after pregnancy.

METHODS

Twelve pregnancies that had complete steady-state data before, during, and after pregnancy were evaluated. Data included weight, LTG dose, and LTG blood levels at preconception, during pregnancy, and postpartum, and concomitant use of other antiepileptic drugs and their dosages. Apparent clearance (L/[kg.day]) of LTG was calculated by dose/level/weight for time points at preconception; during the first trimester, second trimester, and third trimester; and postpartum. Apparent clearance was compared between preconception and each of the three trimesters. Statistical analysis was performed using one-way analysis of variance, the Student-Newman-Keuls test, and the paired Student's t-test.

RESULTS

An increase in apparent clearance (>65%) was observed between preconception and the second and third trimesters (p < 0.05). Eleven pregnancies required higher doses of LTG to maintain therapeutic levels during pregnancy. There was no significant change in apparent clearance between each trimester. A decrease in apparent clearance was observed between the last two trimesters and postpartum (p < 0.05). In the postpartum period, apparent clearances returned to the preconception baseline, and LTG doses needed to be reduced.

CONCLUSION

Pregnancy increases LTG clearance by >50%. This effect occurs early in pregnancy and reverts quickly after delivery. LTG levels should be monitored before, during, and after pregnancy.

Critical re-evaluation of previous preclinical strategies for the discovery and the development of new antiepileptic drugs

During the last decade, several new antiepileptic drugs (AEDs) have been introduced in Europe, the United States, or other parts of the world. Although the antiepileptic efficacy of these drugs is not superior to that of older AEDs, some of the new drugs offer advantages in terms of improved tolerability, ease of use, and reduced interaction potential with other drugs. However, the new AEDs have only a modest impact on patients with refractory epilepsies, so that about one third of patients with epilepsy continue to have seizures with current pharmacotherapies. Thus, there is a continuing need for new medical therapies in epilepsy. During the Workshop on "New Horizons in the Development of Antiepileptic Drugs" (November 28-29, 2001, Philadelphia, PA), one topic dealt with the critical re-evaluation of previous preclinical strategies for the discovery and the development of new AEDs. The discussion of this session, which was chaired by the authors, is summarized in this article. Main issues of the discussion were whether epilepsy is a progressive disease and whether refractory epilepsy is preventable, the use of acute versus chronic animal models in the discovery and development of new AEDs, models for drug-resistant epilepsy, mechanisms of drug resistance, alterations in adverse effect potential of AEDs by epilepsy, and advances in pharmacogenomics and our understanding of pharmacologic responsiveness in epilepsy. Overall, it was felt that the current preclinical strategies for the discovery and development of new AEDs have to be redefined in order to identify agents that are clearly superior to current medications.

Randomized controlled trial of zonisamide for the treatment of refractory partial-onset seizures

BACKGROUND

Zonisamide is a sulfonamide antiepilepsy drug with sodium and calcium channel-blocking actions. Experience in Japan and a previous European double-blind study have demonstrated its efficacy against partial-onset seizures.

METHODS

A randomized, double-blind, placebo-controlled trial enrolling 203 patients was conducted at 20 United States sites to assess zonisamide efficacy and dose response as adjunctive therapy for refractory partial-onset seizures. Zonisamide dosages were elevated by 100 mg/d each week. The study design allowed parallel comparisons with placebo for three dosages and a final crossover to 400 mg/d of zonisamide for all patients. The primary efficacy comparison was change in seizure frequency from a 4-week placebo baseline to weeks 8 through 12 on blinded therapy.

RESULTS

At 400 mg/d, zonisamide reduced the median frequency of all seizures by 40.5% from baseline, compared with a 9% reduction (p = 0.0009) with placebo treatment, and produced a > or =50% seizure reduction (responder rate) in 42% of patients. A dosage of 100 mg/d produced a 20.5% reduction in median seizure frequency (p = 0.038 compared with placebo) and a dosage of 200 mg/d produced a 24.7% reduction in median seizure frequency (p = 0.004 compared with placebo). Dropouts from adverse events (10%) did not differ from placebo (8.2%, NS). The only adverse event differing significantly from placebo was weight loss, though somnolence, anorexia, and ataxia were slightly more common with zonisamide treatment. Serum zonisamide concentrations rose with increasing dose.

CONCLUSION

Zonisamide is effective and well tolerated as an adjunctive agent for refractory partial-onset seizures. The minimal effective dosage was 100 mg/d, but 400 mg/d was the most effective dosage.

Epilepsy in the elderly

The active prevalence rate of epilepsy among persons over 65 years of age is approximately 1.5%, about twice the rate in younger adults. Treatment of epilepsy in the elderly is complicated by alterations in drug metabolism, use of concomitant medications, and multiple medical problems. Drug interactions are a major issue, and a full knowledge of the isoenzyme profile and protein-binding characteristics of each drug (antiepileptic and other) must be known.

Treatment of epilepsy in 3 specialized populations

When discussing the treatment of epilepsy, targeted populations need to be defined. Three patient groups, children, the elderly, and women, are considered "special" because of metabolic and physical differences that require particular care during treatment of this disease. Treatment options vary significantly among these populations. Metabolic differences in very young and elderly patients require close attention by the prescribing physician. Rates of metabolism in children may be much faster than in nonelderly adults, requiring dosing adjustments to ensure enough medication is used to control seizures. Additional concerns with treating children include their increased sensitivity to toxic effects. Elderly patients may have slower metabolic rates because of decreased renal or hepatic function, and thus these patients can easily be overdosed as toxic drug levels build when clearance is reduced. Many elderly patients also may have concomitant illnesses that require other chronic medications. The potential for drug interactions is very high among this population. Women are considered a special population because of issues related to contraception, childbirth, and breast-feeding. Some antiepileptic medications are known to reduce the efficacy of oral contraceptives, and no medication has been proven safe for pregnant women. The pharmacokinetic profiles of many new generation antiepileptic medications may be advantageous to these specialized populations by creating fewer adverse effects, cleaner metabolism, and the reduced risk for drug interactions and teratogenicity.

Monotherapy and polypharmacy

The availability of many new antiepileptic drugs (AEDs) with novel mechanisms of action has made polypharmacy, using combinations of AEDs with differing mechanisms, a viable alternative. The concept of monotherapy in epilepsy is relatively new, having attained widespread use only during the past few decades, and replacing irrational use of combinations of AEDs. In intractable epilepsy, however, monotherapy is often unsuccessful in achieving complete control, and skilled use of AEDs with differing mechanisms may provide better results. Monotherapy remains the treatment method of choice for new-onset epilepsy, but if control is not achieved, rational combinations should be considered. Most critical to successful treatment of epilepsy is the correct identification of the epileptic syndrome.

Incidence and risk factors in sudden unexpected death in epilepsy: a prospective cohort study

OBJECTIVE

To determine incidence of and risk factors for sudden unexpected death in epilepsy (SUDEP).

METHODS

Three epilepsy centers enrolled 4,578 patients and prospectively followed these patients for 16,463 patient-years. The cohort was screened for death annually. Deaths were investigated to determine whether SUDEP occurred. Potential risk factors were compared in SUDEP cases and in controls enrolled contemporaneously at the same center.

RESULTS

Incidence of SUDEP was 1.21/1,000 patient-years and was higher among women (1.45/1,000) than men (0.98/1,000). SUDEP accounted for 18% of all deaths. Occurrence of tonic-clonic seizures, treatment with more than two anticonvulsant medications, and full-scale IQ less than 70 were independent risk factors for SUDEP. The number of tonic-clonic seizures was a risk factor only in women. The presence of cerebral structural lesions and use of psychotropic drugs at the last visit were not risk factors for SUDEP in this cohort. Subtherapeutic anticonvulsant levels at the last visit were equally common in the two groups. No particular anticonvulsant appeared to be associated with SUDEP.

CONCLUSIONS

These results support the idea that tonic-clonic seizures are an important proximate cause of SUDEP. This information creates a risk profile for SUDEP that may help direct preventative efforts.

Absence of pharmacokinetic drug interaction of levetiracetam with phenytoin in patients with epilepsy determined by new technique

Levetiracetam has recently been approved as an adjunctive medication for partial seizures and frequently will be added to phenytoin. The objective of this study was to determine the presence or absence of a pharmacokinetic drug interaction of levetiracetam with phenytoin. A stable isotope tracer technique using deuterium-labeled (D10) phenytoin and high-performance liquid chromatography with ultraviolet detection (rather than mass spectrometric detection) was employed. Tracer doses of D10-phenytoin were administered i.v. before and 12 weeks after adding levetiracetam to the regimen of 6 subjects on phenytoin monotherapy for epilepsy. Blood was collected for 96 hours after each infusion. The following pharmacokinetic parameters were determined for phenytoin: Cmax, Cmin, Cavo, AUC, CL, t 1/2, VD, and free (nonprotein bound) fraction. The ratio and the 90% confidence interval of the ratio of log-transformed mean values for phenytoin pharmacokinetic parameters before (denominator) and after (numerator) adding levetiracetam all fell within the range of 0.85 to 1.17 (two one-sided test). The authors conclude that the addition of levetiracetam did not bring about clinically important changes in phenytoin pharmacokinetic parameters and that it is not necessary to change the phenytoin dosing rate when levetiracetam is added to phenytoin.

Guidelines for nonemergency use of parenteral phenytoin products: proceedings of an expert panel consensus process. Panel on Nonemergency Use of Parenteral Phenytoin Products

This document summarizes the proceedings of an expert panel consensus process addressing the nonemergency use of parenteral phenytoin products for management of seizures in pediatric and adult patients. The algorithm and consensus statements developed by the expert panel emphasize strategies for lowering the probability of adverse events associated with the use of parenteral phenytoin products. Specific patient characteristics are defined to guide administration and monitoring of parenteral phenytoin therapy. The algorithm provides a decision pathway for the selection of the product and the route of administration of phenytoin sodium or fosphenytoin sodium after it has been determined that a parenteral phenytoin product is appropriate. Key factors covered in the algorithm include a list of patient characteristics and considerations necessary to prevent parenteral phenytoin adverse effects during selection of administration route and recommendations for monitoring of parenteral phenytoin therapy once it has been initiated. Situations requiring rapid attainment of high phenytoin concentrations, such as in the management of acute seizures, are not addressed in these guidelines.

Zonisamide

Zonisamide (ZNS) is a broad-spectrum antiepileptic drug in both animal models of epilepsy and patients with epilepsy. It is effective for both localization-related and generalized epilepsies and appears to be particularly potent in progressive myoclonic epilepsy syndromes. Its pharmokinetic profile is favorable, with a long half-life and low protein binding. However, its insolubility may make the development of a parenteral formulation difficult. Its safety profile is good, although teratogenicity in animal models is of concern. Adult doses of 400-600 mg per day in two doses, with blood levels from 20 to 30 mg/ml, appear to be effective.

Safety of tiagabine: summary of 53 trials

We reviewed the clinical safety of tiagabine HCl (TGB), a selective CNS GABA uptake inhibitor, in nearly 3100 patients from 53 separate clinical trials. TGB was found to have no clinically important effect upon hepatic metabolic processes, serum concentrations of concomitant antiepileptic drugs (AEDs), laboratory values, or important interactions with any common non-AEDs. Adverse effects were usually mild and involved the nervous system. TGB is safe and well-tolerated as add-on therapy for the treatment of partial seizures.

Antiepileptic drug use in nursing home residents: effect of age, gender, and comedication on patterns of use

PURPOSE

Examine antiepileptic drug (AED) use in nursing homes by age, gender, and use of comedication that can interact with AEDs.

METHODS

Two point-prevalence evaluations of AED use from computerized medical records of nursing home residents throughout the United States (set 1, 43,757; set 2, 41,386) 65 years and older serviced by PHARMERICA.

RESULTS

10.5% of residents received an AED. Of the age group 65-84 years, 15 % received an AED compared with 6.1% of those 85 years or older (p < 0.001). Gender differences were present; 13.4% of the male residents and 9.4% of the female residents were treated with an AED (p < 0.001). The most frequently prescribed AEDs were phenytoin, carbamazepine, clonazepam, or phenobarbital. The average number of routine medications taken by AED recipients was 5.6, greater than the average of 4.6 for other residents.

CONCLUSIONS

AEDs are extensively prescribed for elderly nursing home residents. Men and persons aged 65-85 years were more likely to receive AEDs than were women or those older than 85 years. AED recipients receive more routine medications than do other residents, including co-medications that alter hepatic metabolism and clinical response. The reasons for age and gender differences are unclear and require further study.

Quality of life of people with epilepsy in the United States

Health care provision in the United States is driven by the fact that most health insurance is commercial and private. This leads to the tendency to view patients as units that will produce a future cash yield. The quality of life (QOL) movement in the United States is in some ways a response to this view and has a role in convincing insurers that new treatments and techniques are worth increased expenditure. In the case of epilepsy, QOL research has become essential in improving the quality of care offered to people with epilepsy. In this review, some of the outcomes of using the Quality of Life in Epilepsy questionnaire are reviewed, the preliminary data from a community-based study of people with epilepsy are described, and recent studies comparing QOL in epilepsy and other neurologic and nonneurologic diseases are discussed. This review illustrates the complexity of QOL issues and the need for the widespread use of QOL measures in people with epilepsy.

Population pharmacokinetics of carbamazepine in adults with epilepsy

STUDY OBJECTIVE

To conduct a population pharmacokinetic analysis of carbamazepine (CBZ).

DESIGN

Retrospective chart review.

SETTING

Ambulatory neurology clinics at three medical centers.

PATIENTS

Patients diagnosed with epilepsy from 1991-1995. The index set included 829 adults receiving CBZ. A separate validation set consisted of 50 patients.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Final regression equations were apparent oral clearance (Cl/F) (L/hr) = (0.0134 x TBW + 3.58), x 1.42 if receiving phenytoin only; x 1.17 if receiving phenobarbital or felbamate; x 1.62 if receiving phenytoin and phenobarbital or felbamate; x 0.749 if age > or = 70 years; apparent volume of distribution (Vd/F) (L) = 1.97 x total body weight; absorption rate constant [hr(-1)] = 0.441. Interindividual variability in Cl/F and Vd/F was 26% and 82%, respectively. Residual variability was 1.8 mg/L. Predictive performance analysis of the validation set provided a mean prediction error of 0.6 mg/L and median absolute error of 2.4 mg/L.

CONCLUSIONS

These routinely collected data provided quantitative estimates of changes in CBZ Cl/F due to comedication and an age-related decrease in Cl/F The derived regression equations reasonably predicted concentrations in a separate validation set.

Tiagabine for complex partial seizures: a randomized, add-on, dose-response trial

OBJECTIVE

To determine the efficacy and tolerability of tiagabine, a new antiepileptic drug (AED) that inhibits gamma-aminobutyric acid (GABA) uptake, at 3 dose levels vs placebo as adjunctive therapy in patients with intractable complex partial seizures (CPS).

DESIGN

Randomized, double-blind, placebo-controlled study with a parallel-group, add-on design, starting with a 12-week unblinded baseline phase followed by a 20-week double-blind treatment phase.

SETTING

Twenty-one US medical centers.

PATIENTS

Patients (N = 297) aged 12 to 77 years, previously diagnosed as having CPS and receiving stable regimens of 1 to 3 hepatic enzyme-inducing AEDs; divalproex sodium or valproic acid was allowed in combination with any of these drugs.

INTERVENTIONS

Placebo or tiagabine 4 times a day at 16, 32, or 56 mg daily.

MAIN OUTCOME MEASURES

Median change in 4-week CPS frequency and adverse events.

RESULTS

Median decreases in 4-week CPS frequency for the 32-mg (-2.2) and 56-mg (-2.8) tiagabine groups were significantly greater than for the placebo (-0.7) group (P = .03 and P < .03, respectively); 20% and 29% of patients in the 32- and 56-mg groups had a 50% or greater reduction in the frequency of CPS vs 4% in the placebo group (P = .002 and P < .001, respectively). Adverse effects were similar for placebo and tiagabine except for a significantly greater incidence of dizziness in the 32-mg tiagabine group, tremor in the 32- and 56-mg groups, abnormal thinking (usually mental lethargy or difficulty concentrating) in the 56-mg group, and depressed mood in the 16- and 56-mg groups.

CONCLUSIONS

Tiagabine is efficacious and well tolerated as adjunctive therapy for CPS; there is a clear dose-response relationship.

Intramuscular fosphenytoin (Cerebyx) in patients requiring a loading dose of phenytoin

Fosphenytoin (Cerebyx), is a water soluble prodrug that is rapidly and completely converted to phenytoin. This study reports the injection-site tolerance and safety of intramuscular fosphenytoin (> 10 mg/kg doses) in 60 patients requiring a phenytoin loading dose. Patients received injections at single or multiple sites with volumes ranging from 4 to 30 ml per injection site. The majority of patients had no irritation (erythema, swelling, tenderness, bruising) or complaints of discomfort related to fosphenytoin injection either after injection (95%) or at follow-up (88%). Irritation, when reported, was mild in all cases. Forty of 60 patients (67%) reported transient side effects, primarily involving the central nervous system, such as nystagmus, dizziness or ataxia, which are commonly associated with phenytoin therapy. All patients received prescribed doses; no patient had an injection(s) stopped due to intolerance or side effects. No serious adverse events occurred with intramuscular fosphenytoin. In this study, intramuscular fosphenytoin was demonstrated to be a safe and well tolerated, and in many instances, a preferable alternative to other means of phenytoin loading.

Tiagabine therapy for complex partial seizures. A dose-frequency study. The Tiagabine Study Group

OBJECTIVE

To evaluate the efficacy and safety of 2 regimens of tiagabine as add-on therapy for patients with complex partial seizures (CPSs) that are refractory to other treatment.

DESIGN

Randomized, double-blind, placebo-controlled, add-on, parallel-group trial with an 8-week baseline period, 12-week experimental period (4 weeks of dose titration and 8 weeks of fixed-dose therapy), and 4-week termination period.

SETTING

Twenty-six centers throughout the United States.

PATIENTS

Three hundred fifty-one patients were enrolled, 318 were entered in the double-blind period, and 271 completed the study.

INTERVENTIONS

Tiagabine, 16 mg 2 times per day (106 patients); tiagabine, 8 mg 4 times daily (105 patients); and placebo (107 patients). The doses of tiagabine were titrated in 3 steps to the fixed dose.

MAIN OUTCOME MEASURE

The median change in the 4-week rate of CPSs from baseline to experimental period.

RESULTS

The median change from baseline was -1.6 CPSs per 4 weeks in the group of patients who were given tiagabine 2 times per day, and it was -1.2 CPSs in the group of patients who were given tiagabine 4 time per day (P = .06 and P = .02, respectively, compared with placebo). The 4-week seizure frequency was reduced by 50% or more in 31% of the patients who were given tiagabine 2 times per day and in 27% of the patients who were given tiagabine 4 times per day vs 10% of the placebo-treated patients (P < or = .001 for each tiagabine-treated group compared with the placebo group). The most frequent adverse events involved the central nervous system and occurred in comparable proportions in the 3 treatment groups. Similar proportions of patients discontinued the study prematurely for adverse events.

CONCLUSIONS

Tiagabine administered 2 and 4 times daily as add-on pharmacotherapy was effective in reducing CPSs in patients with epilepsy whose conditions were refractory to treatment with other antiepileptic agents, and it was well tolerated.

Rational monotherapy for epilepsy

At the present time monotherapy is preferable to polytherapy if the epilepsy can be controlled with a single drug. However, persons with intractable epilepsy may need more than one antiepileptic drug to attain the best seizure control with the fewest side-effects. Although clinical studies have not been performed to identify the best combinations, rational polytherapy would imply combining antiepileptic drugs with different mechanisms of action.

Familial cerebral cavernous angioma: a gene localized to a 15-cM interval on chromosome 7q

Cerebral cavernous angiomas are collections of closely clustered vessels without intervening normal brain parenchyma, with microscopic evidence of hemorrhage, frequently multiple; they are best visualized with magnetic resonance imaging. Familial cerebral cavernous angioma occurs as an autosomal dominant disorder, although carriers of the gene are often asymptomatic. Recently, a gene responsible for familial cerebral cavernous angioma in a large Hispanic kindred was mapped to human chromosome 7q11-22, representing a large segment of DNA containing approximately 33 cM (about 33 million base pairs). This distance did not allow more restricted isolation of the region containing the familial cerebral cavernous angioma gene. In this report, we present a large white kindred with familial cerebral cavernous angioma and confirm the mapping to 7q11-22, including the genetic markers D7S558/D7S1789 and D7S804. Recombination between several markers in the region suggests that the candidate region is distal to D7S804. Combining our results with those previously published, we suggest that the gene is likely to reside within a 15-cM region bounded by markers D7S660 and D7S558/D7S1789. These results should assist the further refinement of the candidate region for familial cerebral cavernous angioma and facilitate the search for the gene.

Cost of refractory epilepsy in adults in the USA

A cost of illness of refractory epilepsy was developed based on estimates supplied by an expert panel of physicians and a review of the current literature. The basic elements of model can be divided into two main components: direct and indirect costs. Direct costs include the medical resource utilization patterns associated with epilepsy care while the indirect costs represent lost productivity associated with the disease. The results of the analysis indicate that an estimated 24,578 incident cases of epilepsy incur a total of $318,582,669; while our prevalence estimates indicate that 335,167 individuals incur a total of $3,905,183,463, in a given year. Direct medical costs account for one-third of the total costs while indirect costs constitute the remaining two-thirds.

Pharmacokinetics of tiagabine as add-on therapy in patients taking enzyme-inducing antiepilepsy drugs

The effect of hepatic enzyme-inducing antiepilepsy drugs (AEDs) on the clinical pharmacokinetics of tiagabine, a new AED, was studied in the steady-state condition. Patients with epilepsy entered this two-day study on a previously stable regimen of one to three enzyme-inducing drugs (phenytoin, phenobarbital, carbamazepine, and/or primidone) and tiagabine.HCl (24, 40, 56, or 80 mg daily). Patients were confined on both days, and serial blood samples were collected. Plasma tiagabine concentrations were determined by high-performance liquid chromatography; pharmacokinetic parameters were calculated using noncompartmental methods. Tiagabine pharmacokinetics were linear at all doses, as substantiated by the lack of significant differences among groups for dose-adjusted Cmax, Cmin, and AUC0-6. Some diurnal variation occurred, as evidenced by a statistically significant time effect for dose-adjusted AUC0-6. The effect was small, however, and possibly not clinically relevant. The harmonic mean half-lives of 3.8 to 4.9 h were remarkably constant across dosages and shorter than those of historical control subjects not taking enzyme-inducing AEDs suggesting that epilepsy patients not taking enzyme-inducing AEDs may require lower tiagabine.HCl doses to achieve the plasma levels observed in patients taking these drugs.

Tiagabine: the safety landscape

Tiagabine (TGB) hydrochloride is a potential new antiepileptic drug (AED) undergoing clinical development. Experience in humans amounts to 1,810 patient-years of exposure. TGB was found to be tolerated in an integrated safety analysis of five double-blind, add-on therapy trials involving approximately 1,000 patients with epilepsy with difficult-to-control seizures with existing AEDs. Discontinuation resulting from adverse events were infrequent, occurring in 15% of patients receiving TGB compared to 5% receiving placebo. The most frequently reported adverse event was dizziness, which was usually transient and did not require medical intervention. Adverse events that were statistically significantly more common with TGB than placebo were dizziness, asthenia, nervousness, tremor, diarrhea, and depression (not major depression). Adverse events were usually mild to moderate in severity and transient, and most were associated with dose titration. The incidence, type, and severity of adverse events in long-term studies were comparable with those in short-term studies. Serious adverse events were uncommon and no idiosyncratic events were reported.

Familial cerebral cavernous angioma: clinical analysis of a family and phenotypic classification

Only a few large families with cerebral cavernous angiomas (CCA) have been reported. We studied 47 members of a four-generation kindred with familial CCA. Thirteen members are affected; of these, eleven (85%) have epilepsy, five (38%) have hearing loss, three (23%) have clinically significant cerebral hemorrhages, one has dementia and progressive pseudobulbar palsy, one has a compressive myelopathy, one has asymptomatic cerebral cavernous angiomas identified by MRI, and another has an adrenal angioma found at autopsy. We developed a phenotypic classification to be used in future gene mapping studies. This classification is based on clinical symptoms, age at onset, concurrent diagnoses, and magnetic resonance imaging (MRI) findings. In the context of this family, this system assigns each member a probability of affectedness that can be used for linkage analysis. We suggest that patients with epilepsy may experience transient poor seizure control due to bleeding from an angioma, and drugs that may induce bleeding from the angiomas, such as valproic acid, should be avoided.

Felbamate

After the first year of clinical experience, felbamate (FBM) appears to be a valuable antiepileptic drug (AED) for the treatment of intractable epilepsy. However, many patients experience side effects that may discourage continued usage. These may be decreased by using a slower dose-escalation schedule and/or by being more aggressive in decreasing co-medication. The most common troublesome side effects are nausea and insomnia. With the recent observation of aplastic anemia, FBM should be considered only for persons with intractable epilepsy under the care of a physician familiar with FBM. Nevertheless, many patients have benefited significantly from FBM and have made a decision to continue receiving FBM at the presently known risk profile. A few more years of experience may be needed to more accurately determine the final place of FBM in the treatment of epilepsy.

Involuntary movement disorders associated with felbamate

Two children developed involuntary movements while taking felbamate as an adjunct to their antiepileptic regimen. One exhibited choreoathetosis and the other an acute dystonic reaction. In both children the symptoms resolved with no recurrence after felbamate discontinuance.

The effect of felbamate on valproic acid disposition

INTRODUCTION

Felbamate is a new antiepileptic drug approved for partial and secondarily generalized seizures.

DESIGN

Subjects with epilepsy (three men and seven women; age range, 20 to 39 years; weight range, 53 to 88 kg) who were previously stabilized with valproic acid, 9.5 to 31.7 mg/kg/day, received both 600 and 1200 mg felbamate twice a day in an open-label, randomized, crossover study.

RESULTS

Coadministration of 1200 or 2400 mg felbamate increased the mean valproic acid area under the curve (from 802.2 to 1025.4 and 1235.9 mg/hr/ml, respectively), peak concentrations (from 86.1 to 115.1 and 133.4 mg/ml, respectively), and average steady-state concentrations (from 66.9 to 85.5 and 103.0 mg/ml, respectively). No changes were observed in valproic acid time to peak concentration or protein binding. Average steady-state felbamate concentrations were 34.7 mg/ml for 600 mg administered twice daily and 61.2 mg/ml for 1200 mg administered twice daily.

CONCLUSION

When felbamate is added to a regimen of valproic acid, valproic acid doses may require reduction because coadministration of felbamate decreased steady-state valproic acid clearance (28% and 54%, respectively; p < 0.01).

Antiepileptic drugs in development: prospects for the near future

Among some 14 new antiepileptic drugs (AEDs), those most extensively tested in humans include felbamate (FBM), gabapentin (GBP), lamotrigine (LTG), oxcarbazepine (OCBZ), vigabatrin (VGB), and zonisamide (ZNS). All are currently marketed in some but not all countries. Although no large, comparative studies on efficacy have been conducted, all of these new AEDs are effective in adult localization-related epilepsies, and some have activity in specific syndromes. Although these drugs all have some CNS side effects, especially when administered in combination with other AEDs, they also all have low toxicity profiles. The availability of AEDs with different mechanisms of action may facilitate rational polytherapy. FBM is not teratogenic in animals. Half-life of FBM in humans is 11-28 h. Daily FBM dosages are 15-45 mg/kg in children and 2,400-4,800 mg in adults. Side effects include insomnia and anorexia, with weight loss. FBM increases phenytoin (PHT) and valproate (VPA) concentrations, and FBM concentration may be affected by other drugs. It is available in the United States for treatment of Lennox-Gastaut syndrome and partial seizures in adults. GBP is very water soluble. Half-life of GBP in humans is 5-7 h and daily dosages range from 900 to 2,400 mg in adults. Few side effects have been observed. GBP is not metabolized by the liver and has no drug interactions. It is available in the United Kingdom and the United States. LTG has no teratogenicity in animal models. Half-life of LTG in humans depends on co-medication: with enzyme inducers it is 15-24 h, and with VPA it is approximately 60 h. LTG dosages are 100-600 mg/day in adults. LTG is available in Europe. OCBZ is rapidly metabolized to 10,11-dihydro-10-hydroxy-carbazepine (MHD), the active compound. Animal studies have shown similar efficacy but superior toxicity to carbamazepine (CBZ) in animal models. For MHD, half-life ranges from 10 to 15 h in patients. OCBZ dosages range from 300 to 1,800 mg/day. VGB is a potent, irreversible inhibitor of GABA transaminase which elevates GABA levels in the CNS. Daily dosages of 2,000-4,000 mg of VGB are needed in adults. Although intramyelinic edema has developed in rats and dogs, it has not yet presented in other mammals or humans. ZNS is a sulfonamide effective in animal models of epilepsy. Half-life of ZNS is 27-36 h. ZNS daily dosage is 400-600 mg. ZNS has been effective in some cases of Baltic myoclonic epilepsy.

Antiepileptics in the elderly. Pharmacoepidemiology and pharmacokinetics

OBJECTIVE

To evaluate antiepileptic (AE) use by nursing home residents.

DATA SOURCES

Medical records for 996 residents from six Minnesota nursing homes (5% of the nursing home residents in the Minneapolis-St Paul area) compared with medication records of 45,405 nursing home residents nationwide serviced by Pharmacy Corporation of America, Boulder, Colo.

STUDY SELECTION

Reports comparing pharmacokinetics in younger adults and elderly volunteers or patients with epilepsy who were given AEs.

DATA SYNTHESIS

Among Minnesota nursing home residents, 7.7% were taking AEs. Usage in a national survey was 10.1%. A review of published studies involving small numbers of elderly subjects or patients given phenytoin sodium, valproic acid, or carbamazepine demonstrates decreased protein binding and intrinsic clearance and increased half-life with advancing age. Concomitant drugs, especially those with central nervous system effects, can lower the concentration at which AEs cause dose-related side effects, thereby narrowing therapeutic ranges.

CONCLUSION

Approximately 10% of nursing home residents receive AEs, usually with other maintenance medications. In 82% of residents receiving an AE, the indication was treatment of a seizure disorder. Other indications included aggressive behavior, essential tremors, and neurologic pain. Age-related alterations in AE pharmacokinetics result in protein-binding changes and decreases in drug elimination. Measurement of unbound drug concentrations may be helpful when altered binding is suspected or clinical response does not correlate with total AE concentration. Concomitant drugs pose the risk for significant drug interactions and adverse reactions. An understanding of the underlying pharmacokinetic processes, including the need of most elderly patients for lower doses and longer dosing intervals, permits more effective management of therapy and reduces the risk for adverse reactions.

Lack of interaction of gabapentin with carbamazepine or valproate

Gabapentin (GBP) studies were conducted in patients with epilepsy receiving carbamazepine (CBZ, n = 12) or valproate (VPA, n = 14) monotherapy. The effects of GBP coadministration on steady-state CBZ or VPA concentrations and of these antiepileptic drugs (AEDs) on GBP pharmacokinetics were investigated. GBP (400 mg) was coadministered every 8 h for 3 1/3 days with CBZ or for 5 1/3 days with VPA. GBP was well tolerated. Mean steady-state plasma CBZ/CBZ-10,11-epoxide (CBZ-E) and serum VPA concentrations before, during, and after GBP administration were not significantly different. Mean steady-state GBP pharmacokinetic parameters during CBZ or VPA coadministration were similar to steady-state parameters reported in healthy subjects. Thus, no pharmacokinetic interaction exists between CBZ or VPA and GBP. No dosage adjustment is necessary when GBP and CBZ or VPA are coadministered.

Antiepileptic medication interactions

This overview of AEM interactions underscores the importance of understanding the pharmacokinetic properties of AEMs and demonstrates the need for careful analysis of AEM concentrations in situations in which combinations of AEMs are used. Although generalizations concerning the clinical significance of drug interactions can be made, major interpatient variations occur. Thus, whenever an AEM is added or deleted, concentrations of drugs should be measured. Refractory individuals or those with multiple seizure types may need polypharmacy, and, under these circumstances, both total and unbound concentrations may need to be measured. New AEMs may have the potential for clinically significant interactions. If these are not identified and understood early, the development and ultimate clinical usefulness of these new agents may be inhibited.

New antiepileptic medications

Several new compounds are undergoing extensive investigation in the United States and Europe. The available animal and human studies suggest that these new antiepileptic drugs are very promising. Some or all of them will be approved for clinical use during the next decade. New antiepileptic drugs offer new options in the treatment of epilepsy. Although there already has been considerable testing of these drugs, additional studies that incorporate traditional medical outcome measures and quality of life measures remain to be done to establish the ultimate role of the new antiepileptic drugs in the treatment hierarchy for epilepsy.

Advances in pharmacotherapy: recent developments in the treatment of epilepsy

Epilepsy is a disorder of the central nervous system in which the clinical symptoms are recurrent seizures. An increased understanding of the underlying mechanism of seizures and more definitive diagnostic procedures have improved the care of the patient with epilepsy. An improved classification of various seizure types, including specific epilepsy syndromes has helped optimize use of the standard antiepileptic drugs. Research on the mechanism of seizures has led to new antiepileptic drugs. More definitive diagnostic procedures have led to more accurate identification of patients likely to benefit from epilepsy surgery. This review focuses on these areas.

Effect of felbamate on carbamazepine and its major metabolites

Felbamate is a novel antiepileptic drug that is now available in the United States. During a previous double-blind, crossover, placebo-controlled safety and efficacy study, concomitant phenytoin concentrations increased, whereas carbamazepine concentrations decreased. We evaluated the effect of felbamate on the concentrations of carbamazepine and of its major metabolites, carbamazepine-10,11-epoxide (epoxide) and carbamazepine-trans-10,11-diol (diol) in 26 patients. After the addition of felbamate, mean epoxide concentrations increased from 1.8 micrograms/ml during placebo or baseline periods to 2.4 micrograms/ml during felbamate treatment (p < 0.05); there was no significant change in diol concentrations. Mean carbamazepine concentrations decreased from 7.5 micrograms/ml during placebo treatment to 6.1 micrograms/ml during felbamate treatment (p < 0.05). Mechanisms that could account for the increase in steady-state epoxide concentrations are induction of carbamazepine metabolism to epoxide, inhibition of the conversion of epoxide to diol, or both.

Felbamate: a double-blind controlled trial in patients undergoing presurgical evaluation of partial seizures

We studied the efficacy and safety of felbamate, an investigational antiepileptic drug, in a unique, double-blind, placebo-controlled trial. Sixty-four patients with refractory partial-onset seizures who completed a routine evaluation for epilepsy surgery met seizure frequency entry criteria. Each patient received felbamate or placebo in addition to the anticonvulsant regimen present at the conclusion of the presurgical evaluation. The treatment phase consisted of an 8-day inpatient period and a 21-day outpatient period. The efficacy variable was time to fourth seizure. The difference in time to fourth seizure was statistically significant (p = 0.028) in favor of felbamate. Eighty-eight percent of the patients in the placebo group had a fourth seizure during the treatment phase compared with 46% of the patients in the felbamate group (p = 0.001). Adverse experiences with felbamate were generally mild or moderate in severity. This trial demonstrated the ability of felbamate to quickly and safely reduce the occurrence of frequent partial-onset seizures and maintain effective seizure control following reductions in the dosages of standard antiepileptic drugs.