Effect of topiramate or carbamazepine on the pharmacokinetics of an oral contraceptive containing norethindrone and ethinyl estradiol in healthy obese and nonobese female subjects

Do lamotrigine and levetiracetam solve the problem of using sodium valproate in women with epilepsy?

Women with epilepsy, especially those of child-bearing age, are faced with difficult choices when it comes to choosing the most suitable antiepileptic drug (AED). This is particularly so for those with idiopathic generalized epilepsies, or those for whom seizure syndrome is not immediately apparent, where sodium valproate is still considered the drug of choice. While with treatment most might expect to become seizure free, without any adverse effects, other considerations for women mean that valproate is usually initially avoided, with other AEDs such as lamotrigine or levetiracetam being chosen in preference. Based on current information, this article attempts to provide an overview on whether or not the availability of these and other broad-spectrum AEDs have solved the difficulties of using valproate in women of child-bearing age.

Neuroendocrinological aspects of epilepsy: important issues and trends in future research

Neuroendocrine research in epilepsy focuses on the interface among neurology, endocrinology, gynecology/andrology and psychiatry as it pertains to epilepsy. There are clinically important reciprocal interactions between hormones and the brain such that neuroactive hormones can modulate neuronal excitability and seizure occurrence while epileptiform discharges can disrupt hormonal secretion and promote the development of reproductive disorders. An understanding of these interactions and their mechanisms is important to the comprehensive management of individuals with epilepsy. The interactions are relevant not only to the management of seizure disorder but also epilepsy comorbidities such as reproductive dysfunction, hyposexuality and emotional disorders. This review focuses on some of the established biological underpinnings of the relationship and their clinical relevance. It identifies gaps in our knowledge and areas of promising research. The research has led to ongoing clinical trials to develop hormonal therapies for the treatment of epilepsy. The review also focuses on complications of epilepsy treatment with antiepileptic drugs. Although antiepileptic drugs have been the mainstay of epilepsy treatment, they can also have some adverse effects on sexual and reproductive function as well as bone density. As longevity increases, the prevention, diagnosis and treatment of osteoporosis becomes an increasingly more important topic, especially for individuals with epilepsy. The differential effects of antiepileptic drugs on bone density and their various mechanisms of action are reviewed and some guidelines and future directions for prevention of osteoporosis and treatment are presented.

Antiepileptic drug interactions - principles and clinical implications

Antiepileptic drugs (AEDs) are widely used as long-term adjunctive therapy or as monotherapy in epilepsy and other indications and consist of a group of drugs that are highly susceptible to drug interactions. The purpose of the present review is to focus upon clinically relevant interactions where AEDs are involved and especially on pharmacokinetic interactions. The older AEDs are susceptible to cause induction (carbamazepine, phenobarbital, phenytoin, primidone) or inhibition (valproic acid), resulting in a decrease or increase, respectively, in the serum concentration of other AEDs, as well as other drug classes (anticoagulants, oral contraceptives, antidepressants, antipsychotics, antimicrobal drugs, antineoplastic drugs, and immunosupressants). Conversely, the serum concentrations of AEDs may be increased by enzyme inhibitors among antidepressants and antipsychotics, antimicrobal drugs (as macrolides or isoniazid) and decreased by other mechanisms as induction, reduced absorption or excretion (as oral contraceptives, cimetidine, probenicid and antacides). Pharmacokinetic interactions involving newer AEDs include the enzyme inhibitors felbamate, rufinamide, and stiripentol and the inducers oxcarbazepine and topiramate. Lamotrigine is affected by these drugs, older AEDs and other drug classes as oral contraceptives. Individual AED interactions may be divided into three levels depending on the clinical consequences of alterations in serum concentrations. This approach may point to interactions of specific importance, although it should be implemented with caution, as it is not meant to oversimplify fact matters. Level 1 involves serious clinical consequences, and the combination should be avoided. Level 2 usually implies cautiousness and possible dosage adjustments, as the combination may not be possible to avoid. Level 3 refers to interactions where dosage adjustments are usually not necessary. Updated knowledge regarding drug interactions is important to predict the potential for harmful or lacking effects involving AEDs.

Implications of obesity for drug therapy: limitations and challenges

Obesity has become a worldwide challenge with significant health and socioeconomic implications. One of the major implications is its impact on drug therapy. In order to gain a better understanding of this impact, we surveyed the regulatory guidances, the newly approved molecular entity drug products, and drug product labels in the Physician's Desk Reference. This review summarizes the findings of the survey along with the existing knowledge on pharmacokinetic and pharmacodynamic changes associated with obesity.

Carbamazepine coadministration with an oral contraceptive: effects on steroid pharmacokinetics, ovulation, and bleeding

PURPOSE

Antiepileptic drugs (AEDs) are widely used in reproductive-age women. The AED carbamazepine (CBZ) induces the hepatic cytochrome P450 system, thereby accelerating hormone metabolism. We sought to assess the pharmacodynamic effects of CBZ on breakthrough bleeding and ovulation during oral contraceptive (OC) use.

METHODS

A double-blind, randomized, crossover study of healthy women ages 18-35 years. Participants took an OC containing 20 μg ethinyl estradiol (EE) and 100 μg levonorgestrel (LNG) for 4 months. Concurrently, participants took 600 mg CBZ or a matching placebo for 2 months each, administered in random order. During the second month of CBZ or placebo, we measured EE and LNG levels 12 times over 24 h, ovarian follicular diameters with eight biweekly vaginal ultrasounds, weekly progesterone levels, and bleeding (using a diary).

KEY FINDINGS

We enrolled 25 women; 10 completed the study. Five women discontinued because of reversible CBZ side effects. Mean area under the curve (AUC) measurements were lower during CBZ use compared to placebo for EE (1,778 vs. 986 pg*h/ml, p < 0.001) and LNG (24.8 vs. 13.8 pg*h/ml, p = 0.04). Ovulation occurred in 5 of 10 CBZ cycles compared to 1 of 10 placebo cycles (p = 0.06). Three or more days of breakthrough bleeding occurred during 8 of the 10 CBZ cycles compared to 2 of the 10 placebo cycles (p = 0.07).

SIGNIFICANCE

A commonly used dose of CBZ decreased levels of contraceptive steroids, increased breakthrough bleeding, and permitted ovulation during use of a low-dose OC. Women treated with CBZ are not adequately protected from pregnancy by low-dose OCs.

Topiramate in the new generation of drugs: efficacy in the treatment of alcoholic patients

Predicated upon a neuropharmacological conceptual model, there is now solid clinical evidence to support the efficacy of topiramate for the treatment of alcohol dependence. Topiramate treatment can be initiated whilst the alcohol-dependent individual is still drinking - just when crisis intervention is most likely to be needed by a patient with or without his or her family asking the health practitioner for assistance. Because topiramate can be paired with a brief intervention, there is now the exciting possibility of treating most alcohol- dependent individuals in office-based practice or generic treatment settings. Topiramate's additional effects on other impulsedyscontrol disorders make it a particularly interesting compound for the treatment of other comorbid drug or psychiatric disorders. Additionally, future studies should explore whether topiramate can be combined with other putative therapeutic agents to increase its efficacy. One notable clinical challenge in the development of topiramate as a pharmacotherapy to treat alcohol dependence is the determination of the smallest dose that can result in efficacy, thereby achieving the optimum balance between therapeutic benefit and adverse event profile. Animal data do provide support for topiramate's general anti-drinking effects but also indicate that its mechanisms of action might rely on several complex pharmacobehavioral changes. Additional preclinical studies are needed to elucidate more clearly the basic mechanistic processes that underlie topiramate's efficacy as a treatment for alcohol dependence. Preclinical information that topiramate may have differential effects based on genetic vulnerability opens up the possibility of future methods to optimize treatment.

Effect of obesity on the pharmacokinetics of drugs in humans

The prevalence of obesity has dramatically increased in recent years and now includes a significant proportion of the world's children, adolescents and adults. Obesity is linked to a number of co-morbidities, the most prominent being type 2 diabetes mellitus. While many agents are available to treat these conditions, the current knowledge regarding their disposition in the obese remains limited. Over the years, both direct and indirect methodologies have been utilized to assess body composition. Commonly used direct measures include underwater weighing, skinfold measurement, bioelectrical impedance analysis and dual-energy x-ray absorptiometry. Unfortunately, these methods are not readily available to the majority of clinicians. As a result, a number of indirect measures to assess body composition have been developed. Indirect measures rely on patient attributes such as height, bodyweight and sex. These size metrics are often utilized clinically and include body mass index (BMI), body surface area (BSA), ideal bodyweight (IBW), percent IBW, adjusted bodyweight, lean bodyweight (LBW) and predicted normal weight (PNWT). An understanding of how the volume of distribution (V(d)) of a drug changes in the obese is critical, as this parameter determines loading-dose selection. The V(d) of a drug is dependent upon its physiochemical properties, the degree of plasma protein binding and tissue blood flow. Obesity does not appear to have an impact on drug binding to albumin; however, data regarding alpha(1)-acid glycoprotein binding have been contradictory. A reduction in tissue blood flow and alterations in cardiac structure and function have been noted in obese individuals. At the present time, a universal size descriptor to describe the V(d) of all drugs in obese and lean individuals does not exist. Drug clearance (CL) is the primary determinant to consider when designing a maintenance dose regimen. CL is largely controlled by hepatic and renal physiology. In the obese, increases in cytochrome P450 2E1 activity and phase II conjugation activity have been observed. The effects of obesity on renal tubular secretion, tubular reabsorption, and glomerular filtration have not been fully elucidated. As with the V(d), a single, well validated size metric to characterize drug CL in the obese does not currently exist. Therefore, clinicians should apply a weight-normalized maintenance dose, using a size descriptor that corrects for differences in absolute CL between obese and non-obese individuals. The elimination half-life (t((1/2))) of a drug depends on both the V(d) and CL. Since the V(d) and CL are biologically independent entities, changes in the t((1/2)) of a drug in obese individuals can reflect changes in the V(d), the CL, or both. This review also examines recent publications that investigated the disposition of several classes of drugs in the obese--antibacterials, anticoagulants, antidiabetics, anticancer agents and neuromuscular blockers. In conclusion, pharmacokinetic data in obese patients do not exist for the majority of drugs. In situations where such information is available, clinicians should design treatment regimens that account for any significant differences in the CL and V(d) in the obese.

Effect of laropiprant, a PGD2 receptor 1 antagonist, on estradiol and norgestimate pharmacokinetics after oral contraceptive administration in women

Laropiprant is a prostaglandin D2 receptor 1 antagonist that is being developed in combination with niacin for the treatment of dyslipidemia. This randomized clinical study evaluated the effect of laropiprant on the pharmacokinetics of ethinyl estradiol (EE) and norelgestromin (NGMN), the principal circulating metabolite of norgestimate, in healthy women receiving 3 or more months of an oral contraceptive (Ortho Tri-Cyclen; Ortho-McNeil Pharmaceutical, Raritan, NJ), which contains EE and norgestimate. Twenty-one female subjects with normal menstrual cycles received the oral contraceptive on Days 1 to 21 during two consecutive contraceptive cycles. Subjects received double-blind 40 mg/day laropiprant or placebo on Days 1 to 21 of each contraceptive cycle. Plasma samples were collected predose and 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, and 24 hours postdose on Day 21 to measure area under the plasma concentration-time curve from 0 to 24 hours (AUC0-24hr) and maximum concentration observed in plasma (Cmax) of EE and NGMN. Comparability would be declared if the 90% confidence intervals for the geometric mean ratio of AUC0-24hr and Cmax in the absence and presence of laropiprant were within predefined bounds (0.80-1.25). The estimated geometric mean ratios (90% confidence intervals) of EE and NGMN, respectively, were 1.08 (1.04-1.13) and 0.97 (0.94-0.99) for AUC0-24hr and 1.16 (1.06-1.27) and 1.00 (0.94-1.06) for Cmax. The 90% confidence intervals for the geometric mean ratio of EE Cmax minimally exceeded the prespecified bounds; the other relevant pharmacokinetic parameters fell within the predefined bounds. Coadministration of 40 mg laropiprant with the oral contraceptive did not lead to clinically meaningful alterations in the pharmacokinetics of EE or NGMN.

Women and epilepsy

Women with epilepsy face additional challenges when compared to their peers. Hormonal influences may increase seizure activity, alter endocrine function, and affect fertility. In this population, antiepileptic drugs (AEDs) reduce the efficacy of contraception methods and increase the risk of fetal malformations. Other pertinent issues to women with epilepsy include breastfeeding as well as bone mineral health. This article summarizes our current, collective knowledge of these issues and makes specific recommendations with respect to management.

Female issues in epilepsy: a critical review

The focus on gender-related issues for women with epilepsy has heightened in recent years. The emphasis, however, has been on the childbearing years. Epilepsy and antiepileptic drug treatment affect sexual development, the menstrual cycle, and aspects of contraception, fertility, and reproduction. Female patients with epilepsy at a reproductive age face a unique set of reproductive issues, ranging from descriptions of disorders of reproduction in epilepsy and its causes, to contraception, pregnancy, sexuality, menopause, and osteoporosis. Conditions and diseases that specifically affect women are discussed. The role of hormones across the life cycle--endogenous and exogenous hormones and their effects on drug interactions, drug metabolism, and therapeutic outcomes--is described. Contraception and pregnancy issues for women with epilepsy have received the appropriate attention.

Antiepileptic drug interactions

INTRODUCTION

Antiepileptics are drugs used in the long-term treatment of epilepsy and other conditions such as pain or psychiatric diseases. They are often administered as polytherapy or in combination with other treatments. It is therefore important to know their potential interactions (with each other and with other substances) in order to avoid altering their efficacy or potentiating their side effects.

OBJECTIVE

The purpose of this article is to review these aspects and stress the most important interactions in day-to-day clinical practice.

RESULTS

Older antiepileptic drugs (AEDs) such as phenytoin, carbamazepine, phenobarbital and valproic acid can significantly interfere not only with each other and other AEDs, but also with other treatments. Although newer AEDs have a more favourable pharmacokinetic profile, they are not entirely exempt from interactions and they are also commonly administered in combination with older AEDs. Another aspect that should be considered is the existence of any clinically important pharmacokinetic and pharmacodynamic interactions in patients requiring the continuous administration of other treatments.

CONCLUSION

We must be aware of the pharmacokinetic and pharmacodynamic interactions of AEDs. Because of a lack of significant interactions, drugs such as levetiracetam, gabapentin or pregabalin can be recommended in particular groups such as patients with cancer, transplants, anticoagulant treatments or HIV infection. In all cases, it is important to ensure AED efficacy and prevent serious complications.

Topiramate for Use in Adult Migraine Prophylaxis

Objective:

To review studies comparing topiramate with placebo or other migraine prophylaxis agents in order to outline the role of topiramate in the pharmacologic prevention of adult migraine and to provide clinicians with evidence for rationale of its use.

Data Sources:

Primary studies and review articles were identified via a MEDLINE search (1960–November 2008). Search terms included topiramate, antiepileptic, anticonvulsant, migraine prophylaxis, and migraine prevention. Additional references were obtained from bibliographies of those resources.

Study Selection and Data Extraction:

All relevant information extracted from randomized, controlled studies and systematic reviews evaluating the efficacy, safety, and pharmacology of topiramate in the prevention of adult migraine were included.

Data Synthesis:

Topiramate is approved for the prevention of adult migraine. It has historically been used in the treatment of seizure disorders but received approval for migraine prophylaxis in 2004. The exact mechanism of its antimigraine effect remains unknown, but modulation of sodium channels, γ-aminobutyric acid, and glutamate activity seem to be involved, given the proposed shared pathophysiology between seizure and migraine. Two pivotal trials comparing topiramate with placebo led to approval for migraine prophylaxis in the US and a third similar trial that compared topiramate with propranolol secured licensure in Europe. Additional studies evaluated optimal dosing up to 200 mg daily and duration of therapy through 14 months. These trials demonstrated the ability of topiramate 50 mg twice daily, administered for up to 14 months, to safely reduce migraine frequency, duration, and severity. Limited information from comparative studies suggests a similar effect of topiramate and other agents, including divalproex sodium, propranolol, and timolol. The most common adverse effect observed among all trials was mild-to-moderate paresthesias that were transient in nature. Other adverse effects commonly reported include gastrointestinal upset and cognitive impairment. Adverse effects were more likely to occur during titration periods. Topiramate's safety profile appears to be as good as or better than that of other prophylactic agents.

Conclusions:

Topiramate is an appropriate first-line drug to consider for prevention of adult migraine. The efficacy and safety of topiramate in migraine prophylaxis has been well established in clinical trials and is comparable with other approved agents for this indication. When choosing among these agents, prescribers should consider the adverse effect profile, route of administration, cost, and comorbidities.

ACPE Universal Program Number:

407-000-09-052-H01-P (Pharmacists); 407-000-09-052-H01-T (Technicians)

Topiramate monotherapy in the treatment of newly or recently diagnosed epilepsy

BACKGROUND

The efficacy of topiramate (TPM) as an adjunctive treatment for epilepsy has been established in placebo-controlled clinical trials. Clinical trials of antiepileptic monotherapy usually evaluate low and high doses of study drug or compare study drug with another active agent.

OBJECTIVE

This article reviews available evidence for the use of TPM as monotherapy in patients with newly or recently diagnosed epilepsy.

METHODS

A search of MEDLINE, EMBASE, BIOSIS, SCISEARCH, and the Cochrane Database of Systematic Reviews (all years) for reports of controlled trials of TPM monotherapy in patients with recently diagnosed (within the previous 3 years) epilepsy was conducted in January 2008 using the terms topiramate, epilepsy, newly diagnosed, recently diagnosed, and monotherapy. Identified trials were included in the review if they were published in peer-reviewed journals and enrolled > or = 20 patients.

RESULTS

Three randomized, double-blind, controlled trials met the criteria for inclusion in the review. In a comparison of TPM 50 and 500 mg/d, the higher dose was associated with significantly greater freedom from seizures at 6 months compared with the lower dose (54% vs 39%, respectively; P = 0.02). The time to first seizure was significantly associated with mean plasma TPM concentrations (P = 0.015). In a comparison of TPM 50 and 400 mg/d, the time to first seizure was significantly longer with the higher dose compared with the lower dose (P<0.001, Kaplan-Meier analysis), and the probability of 12-month seizure freedom was significantly higher (76% vs 59%, respectively; P = 0.001). Again, the time to first seizure was significantly associated with mean plasma TPM concentrations (P = 0.029). In a comparative study of TPM 100 and 200 mg/d, carbamazepine 600 mg/d, and valproate 1250 mg/d, there was no significant difference in rates of 6-month seizure freedom with TPM 100 and 200 mg/d (49% and 44%, respectively), carbamazepine (44%), and valproate (44%). Adverse events in the 3 studies were similar between TPM dose groups, although the incidence generally increased with increasing doses, occurred early in treatment, and decreased with prolonged therapy. In a pooled analysis of the 3 trials, the most commonly occurring adverse events during dose titration were paresthesia (25%), fatigue (16%), dizziness (13%), somnolence (13%), and nausea (10%); the most frequent adverse events during maintenance therapy were headache (20%), decreased appetite (11%), and weight loss (11%).

CONCLUSION

In the 3 studies reviewed, TPM monotherapy was effective and generally well tolerated in patients with newly diagnosed epilepsy.

Modeling, prediction, and in vitro in vivo correlation of CYP3A4 induction

CYP3A4 induction is not generally considered to be a concern for safety; however, serious therapeutic failures can occur with drugs whose exposure is lower as a result of more rapid metabolic clearance due to induction. Despite the potential therapeutic consequences of induction, little progress has been made in quantitative predictions of CYP3A4 induction-mediated drug-drug interactions (DDIs) from in vitro data. In the present study, predictive models have been developed to facilitate extrapolation of CYP3A4 induction measured in vitro to human clinical DDIs. The following parameters were incorporated into the DDI predictions: 1) EC(50) and E(max) of CYP3A4 induction in primary hepatocytes; 2) fractions unbound of the inducers in human plasma (f(u, p)) and hepatocytes (f(u, hept)); 3) relevant clinical in vivo concentrations of the inducers ([Ind](max, ss)); and 4) fractions of the victim drugs cleared by CYP3A4 (f(m, CYP3A4)). The values for [Ind](max, ss) and f(m, CYP3A4) were obtained from clinical reports of CYP3A4 induction and inhibition, respectively. Exposure differences of the affected drugs in the presence and absence of the six individual inducers (bosentan, carbamazepine, dexamethasone, efavirenz, phenobarbital, and rifampicin) were predicted from the in vitro data and then correlated with those reported clinically (n = 103). The best correlation was observed (R(2) = 0.624 and 0.578 from two hepatocyte donors) when f(u, p) and f(u, hept) were included in the predictions. Factors that could cause over- or underpredictions (potential outliers) of the DDIs were also analyzed. Collectively, these predictive models could add value to the assessment of risks associated with CYP3A4 induction-based DDIs by enabling their determination in the early stages of drug development.

Pharmacokinetic interactions between contraceptives and antiepileptic drugs

The occurrence of bi-directional drug interactions between antiepileptic drugs (AEDs) and combined oral contraceptives (OCs) pose potential risks of un-intended pregnancy and as well as seizure deterioration. It is well established that several of the older AEDs (carbamazepine, phenytoin and phenobarbital), are strong inducers of the hepatic cytochrome P450 (CYP) 3A4 enzyme system, and are associated with increased the risk of contraceptive failure. In addition, it is demonstrated that also some of the newer AEDs, oxcarbazepine and topiramate influence on the pharmacokinetics of OCs, which is thought to be due to a more selective induction of subgroups of the hepatic enzyme system. Estrogens containing OCs induce the glucuronosyltransferase and may reduce the plasma levels and the effect of AEDs cleared by glucuronidation. This has been most intensively studied for lamotrigine but also other AEDs, which undergoes glucuronidation processes, such as valproate and oxcarbazepine, may be affected by OCs. The magnitude of the drug-drug interactions show in general wide inter-individual variability and the change in the elimination rate is often unpredictable and can be influenced by a number of co-variants such as co-medication of other drugs, as well as genetic and environmental factors. It is therefore recommended that change in OC use is assisted by AED monitoring whenever possible.

Identification of the human cytochrome P450 enzymes involved in the in vitro biotransformation of lynestrenol and norethindrone

This study examined the cytochrome P450 (CYP) enzyme selectivity of in vitro bioactivation of lynestrenol to norethindrone and the further metabolism of norethindrone. Screening with well-established chemical inhibitors showed that the formation of norethindrone was potently inhibited by CYP3A4 inhibitor ketoconazole (IC(50)=0.02 microM) and with CYP2C9 inhibitor sulphaphenazole (IC(50)=2.13 microM); the further biotransformation of norethindrone was strongly inhibited by ketoconazole (IC(50)=0.09 microM). Fluconazole modestly inhibited both lynestrenol bioactivation and norethindrone biotransformation. Lynestrenol bioactivation was mainly catalysed by recombinant human CYP2C9, CYP2C19 and CYP3A4; rCYP3A4 was responsible for the hydroxylation of norethindrone. A significant correlation was observed between norethindrone formation and tolbutamide hydroxylation, a CYP2C9-selective activity (r=0.63; p=0.01). Norethindrone hydroxylation correlated significantly with model reactions of CYP2C19 and CYP3A4. The greatest immunoinhibition of lynestrenol bioactivation was seen in incubations with CYP2C-Ab. The CYP3A4-Ab reduced norethindrone hydroxylation by 96%. Both lynestrenol and norethindrone were weak inhibitors of CYP2C9 (IC(50) of 32 microM and 46 microM for tolbutamide hydroxylation, respectively). In conclusion, CYP2C9, CYP2C19 and CYP3A4 are the primary cytochromes in the bioactivation of lynestrenol in vitro, while CYP3A4 catalyses the further metabolism of norethindrone.

Pregnancy, epilepsy, and anticonvulsants

The majority of epileptic disorders are not self-limiting over time, and therefore require a long-lasting and often even lifelong antiepileptic drug (AED) treatment, in Wi/omen with epilepsy, the influence of their disease on the possibility and course of pregnancies, as well as the potential impact of the AED treatment on mother and child, are crucial questions.

This review addresses the clinically relevant knovledge concerning the impact of the disease itself and the AED treatment on fertility, pregnancy, delivery, the postpartum period, and teratogenicity. Some of the new AEDs appear to have a favorable profile due to a lack of clinically relevant interactions and promising teratogenic profiles. However, the finding of decreases in lamotrigine serum concentrations during hormonal contraception and pregnancy is an instructive example, shovt/ing that ongoing studies are urgently needed to further investigate stillunanswered questions. Several prospective multinational surveys are currently being performed, and should add essential information in this context.

Characterization of non-linear relationship between total and unbound serum concentrations of valproic acid in epileptic children

OBJECTIVE

To establish a regression equation to properly estimate the unbound serum concentration of valproic acid (VPA) from its total serum concentration; the relationship between total and unbound serum VPA concentrations was retrospectively characterized.

METHODS

Data were obtained from the clinical examination records that were routinely archived during therapeutic drug monitoring. The screening encompassed 342 records of 108 paediatric patients whose total and unbound VPA concentrations had been determined. The relationship between total and unbound VPA concentrations was characterized according to the Langmuir equation by taking account of inter-individual variability with the nonmem program.

RESULTS

The total VPA concentration (C(t)) in the screened patients ranged from 5.5 to 179.8 microg/mL, and the unbound VPA concentration (C(f)) increased in a non-linear manner as the total VPA concentration increased. Taking account of the effects of antiepileptics concurrently administered, the VPA dissociation constant (K(d)) and maximum binding site concentration (B(m)) were 7.8 +/- 0.7 and 130 +/- 4.5 microg/mL respectively, for the regression equation, C(t) = C(f) + B(m) x C(f)/(K(d) + C(f)). An alteration in the unbound concentration was seen in patients who were treated with the combination of VPA and ethosuximide and in those who received two additional antiepileptics.

CONCLUSIONS

A regression equation for estimation of the unbound VPA concentration, based on total VPA concentration collected during routine therapeutic drug monitoring was established. Use of two additional antiepileptics and ethosuximide treatment was considered as potential factors affecting unbound VPA concentration.

Pharmacokinetics and tolerability of voriconazole and a combination oral contraceptive co-administered in healthy female subjects

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

* Voriconazole, a broad-spectrum antifungal drug, is a substrate and inhibitor of CYP2C19 and CYP3A4 isozymes. * Ethinyl oestradiol and norethindrone, components of the combination oral contraceptive drug Ortho-Novum 1/35, also are substrates of cytochrome P450 CYP2C19 and CYP3A4 isozymes. * Because co-administration of voriconazole and Ortho-Novum 1/35 could potentially result in pharmacokinetic interactions that increase systemic exposure of one or both drugs to unsafe levels, clinical studies are needed to define better the two-way pharmacokinetic interaction between these drugs.

WHAT THIS STUDY ADDS

* Although co-administered voriconazole and oral contraceptive did result in increased systemic exposures of all three drugs relative to respective monotherapy, co-administered treatment was generally safe and well tolerated. * It is recommended, however, that patients receiving co-administered voriconazole and oral contraceptives be monitored for the development of adverse events commonly associated with these medications.

AIM

To assess the two-way pharmacokinetic interaction between voriconazole and Ortho-Novum 1/35, an oral contraceptive containing norethindrone 1 mg and ethinyl oestradiol 35 microg.

METHODS

In this open-label, three-period, fixed-sequence study, 16 healthy females received voriconazole (400 mg q12 h, day 1; 200 mg q12 h, days 2-4) (period 1), oral contraceptive (q24 h, days 12-32) (period 2), and combination voriconazole (400 mg q12 h, day 57; 200 mg q12 h, days 58-60) and oral contraceptive (q24 h, days 40-60) (period 3).

RESULTS

Voriconazole geometric mean AUC(tau) and C(max) increased 46% (12 682-18 495 ng h ml(-1); 90% confidence interval [CI] 32, 61) and 14% (2485-2840 ng ml(-1); 90% CI 3, 27), respectively, when co-administered with oral contraceptive vs. voriconazole alone. Ethinyl oestradiol geometric mean AUC(tau) and C(max) increased 61% (1031-1657 ng h ml(-1); 90% CI 50, 72) and 36% (119-161 ng ml(-1); 90% CI 28, 45), respectively, and norethindrone geometric mean AUC(tau) and C(max) increased 53% (116-177 ng h ml(-1); 90% CI 44, 64) and 15% (18-20 ng ml(-1); 90% CI 3, 28), respectively, during voriconazole co-administration vs. oral contraceptive alone. Neither ethinyl oestradiol nor norethindrone levels were reduced in subjects following voriconazole co-administration. Adverse events (AEs) were generally mild, occurring less in subjects receiving voriconazole alone (36 events) vs. oral contraceptive alone (88 events) or combination treatment (68 events); four subjects experienced a severe AE.

CONCLUSIONS

Co-administration of voriconazole and oral contraceptive increased systemic exposures of all analytes relative to respective monotherapy. Although generally safe and well tolerated, it is recommended that patients receiving co-administered voriconazole and oral contraceptive be monitored for development of AEs commonly associated with these medications.

Molecular pharmacodynamics, clinical therapeutics, and pharmacokinetics of topiramate

Topiramate (TPM; TOPAMAX) is a broad-spectrum antiepileptic drug (AED) that is approved in many world markets for preventing or reducing the frequency of epileptic seizures (as monotherapy or adjunctive therapy), and for the prophylaxis of migraine. TPM, a sulfamate derivative of the naturally occurring sugar D-fructose, possesses several pharmacodynamic properties that may contribute to its clinically useful attributes, and to its observed adverse effects. The sulfamate moiety is essential, but not sufficient, for its pharmacodynamic properties. In this review, we discuss the known pharmacodynamic and pharmacokinetic properties of TPM, as well as its various clinically beneficial and adverse effects.

Topiramate in the treatment of partial and generalized epilepsy

Topiramate (TPM) is a widely-used drug for the treatment of epilepsy. It is useful for several types of partial-onset and generalized-onset seizures, and is therefore considered a broad-spectrum agent. It is also effective as a prophylactic against migraine headaches. TPM was first approved for prescription use in 1996. In various countries it is now approved for adjunctive and monotherapy of partial-onset seizures and for therapy of generalized tonic-clonic seizures of nonfocal origin, for children and adults. For initial monotherapy of new-onset seizures, a target dose of 100 mg/day for adults is recommended. Adjunctive use with enzyme-inducing drugs and use for refractory seizures requires higher dosages, though the optimum dose for most patients does not exceed 400 mg/day. Excretion is primarily renal and TPM is not a significant hepatic enzyme inducer. Although it is usually safe and well-tolerated, adverse effects limit use in about 25% of patients. The most salient of these is cognitive dysfunction, especially problems with expressive speech and verbal memory. Weight loss, renal stones, paresthesias and other central nervous system side effects may occur. Tolerability is improved by low initial doses and slow titration to effect.

Topiramate for migraine prophylaxis

Topiramate is one of several antiepileptic drugs that are used in the prevention of migraine, but the only one licensed for use in the UK. Topiramate has an extensive evidence base provided by double-blind, placebo-controlled trials to show that it is a safe, effective and well tolerated drug in the management of migraine. It has also been shown to have a role in the management of chronic migraine, which represents a challenge to primary care clinicians as well as headache specialists. Studies have demonstrated that topiramate can also be effective in preventing migraine in childhood and adolescence, although this is unlicensed in the UK. It has been shown in models both in the US and the UK to offer a cost benefit when direct and indirect costs are evaluated by reducing work loss, improving quality of life and reducing the use of increasingly scarce health resources.

Pharmacology of antiepileptic drugs during pregnancy and lactation

Most women with epilepsy require continuous treatment during pregnancy, making antiepileptic drugs (AEDs) one of the most frequent chronic teratogen exposures. Therapeutic decisions should balance the risks to the developing fetus of AED exposure and of not treating or undertreating the epilepsy. The International AED Pharmacology Work Group of the Health Outcomes in Pregnancy and Epilepsy (HOPE) Forum identified four pharmacology topics critical to enhancing maternal and fetal outcomes for pregnancies exposed to AEDs: (1) hormonal therapies and endogenous changes: bidirectional interactions with AEDs; (2) pharmacokinetic alterations during pregnancy, the role of therapeutic drug monitoring, and the influence on seizure control and maternal and fetal outcomes; (3) multidrug transporters and their various roles during pregnancy; (4) breastfeeding in mothers taking AEDs. The report provides an overview of these key topics, highlights gaps in the current knowledge, and provides future directions for needed research.

Women with epilepsy: hormonal issues from menarche through menopause

Epilepsy is a multilayered disorder complicated by numerous comorbid conditions and hormonal changes. More than 1.5 million girls and women with epilepsy face side effects that are compounded at different ages by menstruation, fertility, pregnancy, fetal health, bone health, and other health issues. Changes in hormonal balance during maturation, from menarche through menopause, affect seizure thresholds and antiepileptic drugs, and vice versa. This overview provides physicians with a background on the multiple issues relevant to women of all ages in the reproductive years, including those planning to conceive and those who are pregnant, and beyond the childbearing years.

Clinical use of antiepileptic drugs at a referral centre for epilepsy

PURPOSE

The National Centre for Epilepsy in Norway admits patients with refractory epilepsy from the whole country. The purpose of this study was to investigate how antiepileptic drugs (AEDs) are used at the centre and compare it with the total consumption in the country and international guidelines regarding clinical use of AEDs.

MATERIAL AND METHODS

A prevalence study was carried out from patient records from 264 patients (136 adults and 128 children). The use of AEDs, gender, polytherapy, common drug combinations, serum concentration measurements, concomitant medication and comorbid conditions were investigated.

RESULTS

Of the 15 AEDs in use, valproate, lamotrigine and levetiracetam were most frequently used. In the country at large, carbamazepine, valproate and lamotrigine were used the most. Valproate and lamotrigine occurred most frequently in combination. In adults, oxcarbazepine and topiramate were used more frequently in women than in men. Children used benzodiazepines three times as often as adults. Newer AEDs were mostly used for partial seizures, in accordance with international guidelines. Thirty-five percent of adults and 20% of children suffered from comorbid CNS-related conditions. The use of concomitant medication was widespread. Serum concentrations were in accordance to recommended therapeutic ranges.

CONCLUSION

The results demonstrate that newer AEDs were much more frequently used at the epilepsy centre than in the country as a whole. The use of polytherapy was common, and therapeutic drug monitoring was used for optimal individualized drug treatment. AEDs were used in accordance to international guidelines and recommendations, which can serve as a reference for other prescribers.

Oral Contraceptives Induce Lamotrigine Metabolism: Evidence from a Double-blind, Placebo-controlled Trial

PURPOSE

This study evaluates the effect of oral contraceptives on lamotrigine (LTG) plasma concentrations and urine excretion of LTG metabolites in a double-blind, placebo-controlled, crossover study in patients with epilepsy.

METHODS

Women with epilepsy, treated with LTG in monotherapy and taking combination-type oral contraceptives, were randomized to treatment with placebo or a standard combination-type contraceptive pill. The dose-corrected trough plasma concentration of LTG and the ratio of N-2-glucuronide/unchanged LTG on urine after 21 days of concomitant placebo treatment was analyzed versus those after 21 days of concomitant treatment with the oral contraceptive pill.

RESULTS

The mean dose-corrected LTG concentration after placebo treatment was 84%[95% confidence interval (CI), 45-134%] higher than after oral contraceptives, signifying an almost doubling of the concentration after cessation of oral contraceptives. Most of this increase took place within the first week after oral contraceptives were stopped. The N-2-glucuronide/LTG ratio in the urine was decreased by 31% (95% CI, -20-61%) when shifting from oral contraceptives to placebo.

CONCLUSIONS

Cessation of oral contraceptives leads to an 84% increase in the concentration of LTG. In parallel, the excretion of the N-2-glucuronide was decreased, indicating that the changes are caused by altered LTG glucuronidation. The change in LTG concentrations was observed within 1 week of the shift of treatment, suggesting that induction and deinduction of LTG glucuronidation is faster than that seen for other metabolic pathways (e.g., cytochrome P450).

A Comparative Pharmacokinetic Study in Healthy Volunteers of the Effect of Carbamazepine and Oxcarbazepine on Cyp3a4

PURPOSE

Carbamazepine (CBZ) and oxcarbazepine (OXCZ) are well-known inducers of drug metabolism via CYP3A4. Indirect interaction studies and clinical experience suggest that CBZ has a stronger potential in this regard than OXCZ. However this has never been subject to a direct comparative study. We performed a study in healthy volunteers to investigate the relative inductive effect of CBZ and OXCZ on CYP3A4 activity using the metabolism of quinidine as a biomarker reaction.

METHODS

Ten healthy, male volunteers participated in an open, randomized crossover study consisting of two periods separated by a 4-week wash-out period. The subjects received 1200 mg oral OXCZ daily for 17 days and 800 mg oral CBZ for 17 days. A single 200 mg oral dose of quinidine was administered at baseline and following administration of CBZ and OXCZ. Outcome parameters were the formation clearance of 3-hydroxyquinidine dose and the ratio of the AUCs of 3-hydroxyquinidine to quinidine.

RESULTS

Formation clearance of 3-hydroxyquinidine was increased by means of 89% (CI: 36-164; p=0.0022) and 181% (CI: 120-260, p<0.0001) after treatment with OXCZ and CBZ, respectively, compared to baseline. The relative inductive effect of CBZ was 46% higher than for OXCZ. AUC ratio increased by means of 161% (CI: 139-187, p<0.0001) (OXCZ) and 222% (CI: 192-257, p<0.0001) (CBZ). Quinidine Cmax decreased by means of 29% (CI: 16-40, p=0.0018) (OXCZ) and 33% (CI: 18-45, p=0.0020) (CBZ). T1/2 decreased by means of 12% (CI: 6-17, p<0.0014) (OXCZ) and 32% (CI: 25-38, p<0.0001) (CBZ). tmax was not changed in either period.

CONCLUSION

We confirm a clinically significant inductive effect of both OXCZ and CBZ. The inductive effect of CBZ was about 46% higher than that of OXCZ, a difference that may be of clinical relevance.

Pharmacokinetic Drug Interactions Involving 17??-Ethinylestradiol

17alpha-Ethinylestradiol (EE) is widely used as the estrogenic component of oral contraceptives (OC). In vitro and in vivo metabolism studies indicate that EE is extensively metabolised, primarily via intestinal sulfation and hepatic oxidation, glucuronidation and sulfation. Cytochrome P450 (CYP)3A4-mediated EE 2-hydroxylation is the major pathway of oxidative metabolism of EE. For some time it has been known that inducers of drug-metabolising enzymes (such as the CYP3A4 inducer rifampicin [rifampin]) can lead to breakthrough bleeding and contraceptive failure. Conversely, inhibitors of drug-metabolising enzymes can give rise to elevated EE plasma concentrations and increased risks of vascular disease and hypertension. In vitro studies have also shown that EE inhibits a number of human CYP enzymes, such as CYP2C19, CYP3A4 and CYP2B6. Consequently, there are numerous reports in the literature describing EE-containing OC formulations as perpetrators of pharmacokinetic drug interactions. Because EE may participate in multiple pharmacokinetic drug interactions as either a victim or perpetrator, pharmaceutical companies routinely conduct clinical drug interaction studies with EE-containing OCs when evaluating new chemical entities in development. It is therefore critical to understand the mechanisms underlying these drug interactions. Such an understanding can enable the interpretation of clinical data and lead to a greater appreciation of the profile of the drug by physicians, clinicians and regulators. This article summarises what is known of the drug-metabolising enzymes and transporters governing the metabolism, disposition and excretion of EE. An effort is made to relate this information to known clinical drug-drug interactions. The inhibition and induction of drug-metabolising enzymes by EE is also reviewed.

Clinically relevant drug interactions with antiepileptic drugs

Some patients with difficult-to-treat epilepsy benefit from combination therapy with two or more antiepileptic drugs (AEDs). Additionally, virtually all epilepsy patients will receive, at some time in their lives, other medications for the management of associated conditions. In these situations, clinically important drug interactions may occur. Carbamazepine, phenytoin, phenobarbital and primidone induce many cytochrome P450 (CYP) and glucuronyl transferase (GT) enzymes, and can reduce drastically the serum concentration of associated drugs which are substrates of the same enzymes. Examples of agents whose serum levels are decreased markedly by enzyme-inducing AEDs, include lamotrigine, tiagabine, several steroidal drugs, cyclosporin A, oral anticoagulants and many cardiovascular, antineoplastic and psychotropic drugs. Valproic acid is not enzyme inducer, but it may cause clinically relevant drug interactions by inhibiting the metabolism of selected substrates, most notably phenobarbital and lamotrigine. Compared with older generation agents, most of the recently developed AEDs are less likely to induce or inhibit the activity of CYP or GT enzymes. However, they may be a target for metabolically mediated drug interactions, and oxcarbazepine, lamotrigine, felbamate and, at high dosages, topiramate may stimulate the metabolism of oral contraceptive steroids. Levetiracetam, gabapentin and pregabalin have not been reported to cause or be a target for clinically relevant pharmacokinetic drug interactions. Pharmacodynamic interactions involving AEDs have not been well characterized, but their understanding is important for a more rational approach to combination therapy. In particular, neurotoxic effects appear to be more likely with coprescription of AEDs sharing the same primary mechanism of action.

Management of epilepsy in women of childbearing age: practical recommendations

Women with epilepsy should not be discouraged from becoming pregnant as the likelihood of having a healthy baby is very high. However, in such women, early and individualised counselling about pregnancy and contraception is essential. Ideally, pregnancies should be planned, folic acid (5 mg/day) given and antiepileptic drug (AED) treatment optimised well before conception to ensure that the lowest dosage that controls seizures is administered. When initiating AEDs in a woman of childbearing age, the most appropriate drug for the seizure type and syndrome should be chosen, although it is preferable to avoid valproate, because of a possible elevated risk of fetal malformations, when equi-effective agents are available for a given syndrome. In women who become pregnant while taking AEDs, fetal monitoring should include high-resolution ultrasonography before week 20 and measurement of serum alpha-fetoprotein levels. Amniocentesis is not routinely indicated. The measurement of blood concentrations of AEDs can be useful to ensure that the lowest possible maintenance dosage is being used, especially for those drugs whose pharmacokinetics are likely to change during pregnancy. Breastfeeding should be encouraged whatever the treatment administered.

The impact of antiepileptic drug therapy on steroidal contraceptive efficacy

Women with epilepsy face unique challenges in maintaining steroidal contraceptive efficacy because some antiepileptic drugs (AEDs) increase the rate of hepatic metabolism of contraceptive steroids, leading to higher potential for contraceptive failure in this population. Planned pregnancy is of great clinical and social importance for women with epilepsy because of the increased risk of birth defects from fetal exposure to AEDs. Current clinical guidelines for contraceptive management in women with epilepsy provide misleading information by focusing on the estrogen content of the formulation, which regulates the menstrual cycle, rather than on the progestin content of the formulation, which provides contraceptive efficacy. This article reviews studies of AED-contraceptive interaction and misconceptions about maintaining contraceptive efficacy and makes recommendations for contraceptive management in women with epilepsy who receive concomitant AED therapy.

The pharmacokinetics and interactions of new antiepileptic drugs: an overview

In the past decade 10 new antiepileptic drugs (AEDs)have been introduced: felbamate, gabapentin, lamotrigine, levetiracetem, oxcarbazepine, pregabalin, tiagabine, topiramate, vigabatrin,and zonisamide. The pharmacokinetics (PK) of these new AEDs as well as their potential for drug interactions are reviewed in this article. In general, new AEDs have better PK profiles and are less involved in drug interactions than the 4 established AEDs: phenobarbital,phenytoin, carbamazepine, and valproic acid. However, in spite of the large therapeutic arsenal of old and new AEDs, about 30% of epileptic patients are still not seizure-free, and thus, there is a substantial need to develop new AEDs.

Uses of topiramate in the treatment of alcohol dependence

Alcohol dependence is a major cause of morbidity and mortality in the USA and throughout the world. Over the last 10 years there has been an intense interest in developing pharmacotherapies that address the neurochemistry of alcohol dependence. Using a novel pharmacological approach to treating alcohol dependence, topiramate (Topamax, Ortho-McNeil Pharmaceutical) has recently been shown to improve the drinking outcomes of alcohol-dependent individuals. This drug profile highlights the scientific concepts and clinical evidence in the development of topiramate for treating alcohol dependence.

Optimizing epilepsy management in teenagers

Optimal epilepsy management in teenage patients represents a particular challenge. These patients are often likely to respond more positively to a regimen that least disrupts their activities. In addition, as a patient group, they are more sensitive to peer perception. Current perceptions of older antiepilepsy drugs do not take into account frequent undesirable side effects or potential adverse interactions with other drugs. Furthermore, they often do not completely control seizures. Recent data suggest that not only do the newer antiepileptic drugs appear to be as efficacious as the older drugs, they also often have more favorable cognitive, cosmetic, and teratogenic side-effect profiles. In addition, newer antiepileptic drugs are being used more often in monotherapy. Successful management of epilepsy in teenagers requires that physicians not only understand the advantages that the newer antiepileptic drugs appear to provide but also consider the social impact of treatment on their patients.

Recent advances in the development of treatments for alcohol and cocaine dependence: focus on topiramate and other modulators of GABA or glutamate function

Neuroscientific developments have promulgated interest in developing efficacious medications for the treatment of substance dependence. Previous pharmacological strategies that involve the use of relatively specific medications to alter corticomesolimbic dopaminergic neuronal activity--the critical pathway for expression of the reinforcing effects of abused drugs--have yielded modest efficacy in the treatment of alcohol dependence, and no medication has been established as a treatment for cocaine dependence. Since corticomesolimbic dopaminergic neurons interact with other neurotransmitters that modulate the effects of dopamine in the nucleus accumbens, would it not be possible to control these dopaminergic effects more reliably with a medication that acts contemporaneously on more than one neuromodulator of dopaminergic function? Further, since the long-term use of either alcohol or cocaine results in neuronal adaptations as a result of sensitisation, would the chances of effective therapy not be bolstered by administering a medication that was also able to mitigate these chronic effects? Thus, a new conceptual approach is needed. My proposal is that a medication--in this case topiramate--that principally potentiates inhibitory GABA(A) receptor-mediated input and antagonises excitatory glutamatergic afferents to the corticomesolimbic dopaminergic system should have therapeutic potential in treating either alcohol or cocaine dependence or perhaps both. This is because the principal neurochemical effects of topiramate would not only serve to decrease the acute reinforcing effects of alcohol or cocaine, but might also facilitate cessation of their use following a period of long-term use by decreasing neuronal sensitisation. This overview highlights the scientific concepts and clinical evidence for the development of topiramate in the treatment of alcohol dependence and introduces preliminary evidence to indicate that it might also have utility in treating cocaine dependence. Finally, to place the material on topiramate in context, information has been included on the utility and development of other medications that modulate GABA- or glutamate-mediated neuronal systems for the treatment of alcohol or cocaine dependence.

Induction of endogenous pathways by antiepileptics and clinical implications

The aim of this study was to review modifications of the endogenous pathways (e.g. enzyme elevations, normal body constituent depletion or higher formation/excretion of endogenous metabolites) which could be ascribed to enzyme induction by antiepileptic drugs (AEDs). Information on older (e.g. phenobarbital, phenytoin and carbamazepine) and newer drugs (where information is available) is discussed together with clinical implications. The enzymes involved in the endogenous pathways and induced by the AEDs will not be limited to the hepatic microsomal enzymes; extrahepatic enzymes and/or enzymes present in other subcellular fractions will also be discussed, if pertinent. The induction of endogenous pathways by AEDs has been taken into account in the past, but much less emphasis has been given compared with the extensive literature on induction by AEDs of the metabolism of concomitantly administered drugs, either of the same or of different classes. Not all of the endogenous pathways examined and induced by AEDs appear to result in serious clinical consequences (e.g. induction of hepatic ALP, increased excretion of d-glucaric acid or of 6 beta-hydroxycortisol). In some cases, induction of some pathways (e.g. increase of high-density lipoprotein cholesterol or of conjugated bilirubin) might even be a beneficial side-effect, however enzyme induction is considered rather a detrimental aspect for an AED, as induction is generally a broad and a non-specific phenomenon. The new AEDs have generally less induction potential than the older agents. Yet some (felbamate, topiramate, oxcarbazepine and lamotrigine) have the potential for inducing enzymes, whereas others (levetiracetam, gabapentin and vigabatrin) appear to be completely devoid of enzyme inducing characteristics, at least as far as the enzymes investigated are concerned.

Traitement médicamenteux de fond de la migraine

Prophylactic treatment is mainly intended to reduce the frequency of migraine attacks. Based on the results of published controlled trials, the main prophylactic drugs are some beta-blockers, methysergide, pizotifene, oxetorone, flunarizine, amitriptyline, NSAIDs, sodium valproate and topiramate. With these drugs, the frequency of attacks can be reduced by half in 50 percent of patients. Some less evaluated substances such as aspirin, DHE, indoramine, and angiotensin II inhibitors may be useful. The decision to treat with drugs and the choice of a prophylactic drug are made together with the patient. The superiority of one major drug over another has never been demonstrated in a comparative trial, thus the choice of the drug to start with depends on the possible side effects and contraindications, the characteristics of the migraine attacks, and the associated morbidities and possible interactions with abortive medications. Doses should be increased gradually, in order to reach the recommended daily dose, only if tolerance permits. Treatment efficacy has to be assessed after 2 or 3 months, and in case of failure or poor tolerance, another treatment should be started. If the treatment is successful, it should be continued for 6 to 12 months, and then tapered off. The moderate efficacy and the frequency of the side effects observed with prophylactic drugs explain the high rate of withdrawals. Some patients nevertheless dramatically improve, warranting trying several drugs successively in order to find the most appropriate one.

Effect of zonisamide on the pharmacokinetics and pharmacodynamics of a combination ethinyl estradiol-norethindrone oral contraceptive in healthy women

BACKGROUND

Several antiepileptic drugs have clinically significant pharmacokinetic interactions with oral contraceptives (OCs) that may result in contraceptive failure.

OBJECTIVE

The aim of this study was to assess the effect of zonisamide on the pharmacokinetics of the individual components of a combination OC (ethinyl estradiol [EE] 0.035 mg and norethindrone [NOR] 1 mg) and on pharmacodynamic variables that may be increased in the event of reduced contraceptive efficacy (concentrations of serum luteinizing hormone [LH], follicle-stimulating hormone [FSH], and progesterone).

METHODS

This was a single-center, open-label, 1-sequence, crossover study. Healthy, premenopausal women received the combination OC for three 28-day cycles (combination OC for 21 days, followed by placebo for 7 days). Following stabilization on the OC during the first cycle, blood was collected during cycle 2 for the determination of serum EE and NOR profiles (day 14) and serum LH, FSH, and progesterone concentrations (days 13-15). Starting on day 15 of cycle 2, zonisamide was administered orally at 100 mg/d and titrated to a target dose of 400 mg/d. EE and NOR profiles and serum LH, FSH, and progesterone concentrations were obtained again in cycle 3 (in the presence of zonisamide) and compared with those from cycle 2 (in the absence of zonisamide).

RESULTS

Thirty-seven healthy premenopausal women (mean age, 26.1 years [range, 18-51 years]; mean body weight, 65.5 kg [range, 50.4-93.1 kg]; mean height, 165.8 cm [range, 152.4-182.9 cm]) received > or =1 dose of zonisamide. Of the 33 subjects (89.2%) who completed the study, 26 (78.8%) underwent titration to a stable zonisamide dose of 400 mg/d. For EE, the mean (SD) AUC over a 24-hour dosing interval (AUC(tau)) was 1139 (317) pg.h/mL in cycle 2 and 1143 (312) pg.h/mL in cycle 3; the mean C(max) in the respective cycles was 133 (39) and 141 (46) pg/mL. For NOR, the corresponding values were 140 (48) and 159 (46) ng.h/mL for AUC(tau) and 21 (5.4) and 23 (6.7) ng/mL for C(max). The 90% Cls for the geometric mean ratios (cycle 3:cycle 2) for AUC(tau) and C(max) fell within the accepted range for lack of interaction (0.80-1.25). There were no increases in LH, FSH, or progesterone concentrations between cycle 2 and cycle 3.

CONCLUSIONS

In these healthy volunteers, steady-state zonisamide dosing had no clinically significant effect on the pharmacokinetics of EE or NOR. There was no pharmacodynamic evidence that zonisamide is likely to reduce the contraceptive effectiveness of OCs containing EE and NOR.

Practical Use of Topiramate for Migraine Prevention

When treating patients with migraine, clinicians should consider prescribing appropriate combinations of acute and preventive therapies. An effective migraine-preventive therapy should be prescribed to patients with frequent (> or = 2 migraines per month) or severe migraine. Topiramate has been shown to be an effective and generally well-tolerated migraine prophylaxis (preventive) therapy in adults, as demonstrated in several large, controlled trials. The most common adverse events in these trials were paresthesia, fatigue, anorexia, nausea, taste alteration, and diarrhea. Most adverse events were mild to moderate and transient in nature. Although patients should take migraine-preventive medications for approximately 2 to 3 months before evaluating effect, topiramate has shown efficacy as early as the first month of treatment. This article describes "real-world" approaches to using topiramate as a migraine-preventive therapy. Topiramate has received regulatory approval for the prophylaxis of migraine headache in adults in the United States and many other countries. The practical issues discussed in this article will enable clinicians to maximize the effectiveness while minimizing the side effects associated with this preventive agent.

Topiramate monotherapy in epilepsy and migraineprevention

OBJECTIVES

The purposes of this review were to assess the efficacy of topiramate as monotherapy for epilepsy and migraine prevention, describe how it should be used, and give clinical advice on how to manage the practical aspects of dosing, titration, and possible adverse events in these 2 indications.

METHODS

We searched the PubMed and BIOSIS databases using the key words topiramate, epilepsy, and migraine from the year 1987 onward, and subsequently focused the search on larger controlled trial studies of topiramate as monotherapy.

RESULTS

Studies have evaluated the use of topiramate as monotherapy in the treatment of partial-onset and generalized seizures and in the prevention of migraine. In a randomized study, 75% of epilepsy patients treated with 400 mg/d topiramate remained seizure free at 1 year. Patients in the same study treated with a lower dose of topiramate (50 mg/d) also experienced notable seizure reductions, with 59% of patients free of seizures at 1 year. A comparison trial of topiramate (100 or 200 mg/d), valproate, and carbamazepine found that topiramate was associated with a similar time to first posttreatment seizure as the other 2 agents (P = NS). Trials of topiramate monotherapy in migraine prevention found that 100 mg/d was associated with a > or =50% reduction in monthly migraine frequency in 49% to 54% of patients. The migraine prevention trials typically used a starting dose of 25 mg/d, with weekly increases of 25 mg and an initial monotherapy target dose of 100 mg/d. The most common adverse events associated with topiramate are paresthesia, weight loss, and other centrally mediated symptoms, many of which may be ameliorated by proper titration and dosing and by good communication between physician and patient.

CONCLUSIONS

Data from controlled trials suggest that 100 mg/d topiramate as monotherapy is effective in the treatment of partial-onset and generalized seizures and in the prevention of migraine.

Pharmacokinetic interactions of topiramate

Topiramate is a new antiepileptic drug (AED) that has been approved worldwide (in more than 80 countries) for the treatment of various kinds of epilepsy. It is currently being evaluated for its effect in various neurological and psychiatric disorders. The pharmacokinetics of topiramate are characterised by linear pharmacokinetics over the dose range 100-800 mg, low oral clearance (22-36 mL/min), which, in monotherapy, is predominantly through renal excretion (renal clearance 10-20 mL/min), and a long half-life (19-25 hours), which is reduced when coadministered with inducing AEDs such as phenytoin, phenobarbital and carbamazepine. The absolute bioavailability, or oral availability, of topiramate is 81-95% and is not affected by food. Although topiramate is not extensively metabolised when administered in monotherapy (fraction metabolised approximately 20%), its metabolism is induced during polytherapy with carbamazepine and phenytoin, and, consequently, its fraction metabolised increases. During concomitant treatment with topiramate and carbamazepine or phenytoin, the (oral) clearance of topiramate increases 2-fold and its half-life becomes shorter by approximately 50%, which may require topiramate dosage adjustment when phenytoin or carbamazepine therapy is added or discontinued. From a pharmacokinetic standpoint, topiramate is a unique example of a drug that, because of its major renal elimination component, is not subject to drug interaction due to enzyme inhibition, but nevertheless is susceptible to clinically relevant drug interactions due to induction of its metabolism. Unlike old AEDs such as phenytoin and carbamazepine, topiramate is a mild inducer and, currently, the only interaction observed as a result of induction by topiramate is that with ethinylestradiol. Topiramate only increases the oral clearance of ethinylestradiol in an oral contraceptive at high dosages (>200 mg/day). Because of this dose-dependency, possible interactions between topiramate and oral contraceptives should be assessed according to the topiramate dosage utilised. This paper provides a critical review of the pharmacokinetic interactions of topiramate with old and new AEDs, an oral contraceptive, and the CNS-active drugs lithium, haloperidol, amitriptyline, risperidone, sumatriptan, propranolol and dihydroergotamine. At a daily dosage of 200 mg, topiramate exhibited no or little (with lithium, propranolol and the amitriptyline metabolite nortriptyline) pharmacokinetic interactions with these drugs. The results of many of these drug interaction studies with topiramate have not been published before, and are presented and discussed for the first time in this article.

Progress report on new antiepileptic drugs: a summary of the Seventh Eilat Conference (EILAT VII)

The Seventh Eilat Conference on New Antiepileptic Drugs (AEDs) (EILAT VII) took place in Villasimius, Sardinia, Italy from the 9th to 13th May 2004. Basic scientists, clinical pharmacologists and neurologists from 24 countries attended the conference,whose main themes included advances in pathophysiology of drug resistance, new AEDs in pediatric epilepsy syndromes, modes of AED action and spectrum of adverse effects and a re-appraisal of comparative responses to AED combinations. Consistent with previous formats of this conference, the central part of the conference was devoted to a review of AEDs in development, as well as updates on second-generation AEDs. This article summarizes the information presented on drugs in development, including atipamezole, BIA-2-093, fluorofelbamate, NPS 1776, pregabalin, retigabine, safinamide, SPM 927, stiripentol, talampanel,ucb 34714 and valrocemide (TV 1901). Updates on felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine,topiramate, vigabatrin, zonisamide, new oral and parenteral formulations of valproic acid and SPM 927 and the antiepileptic vagal stimulator device are also presented.