Effects of felbamate on the pharmacokinetics of a low-dose combination oral contraceptive

Epilepsy and Pregnancy

PURPOSE OF REVIEW

Seizure disorders are the most frequent major neurologic complication in pregnancy, affecting 0.3% to 0.8% of all gestations. Women of childbearing age with epilepsy require special care related to pregnancy. This article provides up-to-date information to guide practitioners in the management of epilepsy in pregnancy.

RECENT FINDINGS

Ongoing multicenter pregnancy registries and studies continue to provide important information on issues related to pregnancy in women with epilepsy. Valproate poses a special risk for malformations and cognitive/behavioral impairments. A few antiseizure medications pose low risks (eg, lamotrigine, levetiracetam), but the risks for many antiseizure medications remain uncertain. Although pregnancy rates differ, a prospective study found no difference in fertility rates between women with epilepsy who were attempting to get pregnant and healthy controls. During pregnancy, folic acid supplementation is important, and a dose greater than 400 mcg/d during early pregnancy (ie, first 12 weeks) is associated with better neurodevelopmental outcome in children of women with epilepsy. Breastfeeding is not harmful and should be encouraged in women with epilepsy even when they are on antiseizure medication treatment.

SUMMARY

Women with epilepsy should be counseled early and regularly about reproductive health. Practitioners should discuss the risks of various obstetric complications; potential anatomic teratogenicity and neurodevelopmental dysfunction related to fetal antiseizure medication exposure; and a plan of care during pregnancy, delivery, and postpartum. Women with epilepsy should also be reassured that the majority of pregnancies are uneventful.

Epilepsy and pregnancy: What should the neurologists do?

Epilepsy is one of the most common chronic disorders affecting women of childbearing age. Unfortunately, many women with epilepsy (WWE) still report not receiving key information about pregnancy. They obviously need information about epilepsy and pregnancy prior to conception with a particular emphasis on effective birth control (i.e. contraception), necessity to plan pregnancy, antiepileptic drugs optimization, and folate supplementation. The risks associated with use of antiepileptic drugs during pregnancy have to be balanced against fetal and maternal risks associated with uncontrolled seizures. This report reviews evidence-based counseling and management strategies concerning maternal and fetal risks associated with seizures, teratogenic risks associated with antiepileptic drug exposure with a special emphasis on developmental and behavioural outcomes of children exposed to intra utero antiepileptic drugs.

Drug-Drug Interaction Studies With Oral Contraceptives: Pharmacokinetic/Pharmacodynamic and Study Design Considerations

Oral contraceptives (OCs) are the most widely used form of birth control among women of childbearing potential. Knowledge of potential drug-drug interactions (DDIs) with OCs becomes imperative to provide information on the medication to women of childbearing potential and enable their inclusion in clinical trials, especially if the new molecular entity is a teratogen. Although a number of DDI guidance documents are available, they do not provide recommendations for the design and conduct of OC DDI studies. The evaluation of DDI potential of a new molecular entity and OCs is particularly challenging because of the availability of a wide variety of combinations of hormonal contraceptives, different doses of the ethinyl estradiol, and different metabolic profiles of the progestin component. The aim of this review is to comprehensively discuss factors to be considered such as pharmacokinetics (PK), pharmacodynamics (PD), choice of OC, and study population for the conduct of in vivo OC DDI studies. In this context, metabolic pathways of OCs, the effect of enzyme inhibitors and inducers, the role of sex hormone-binding globulin in the PK of progestins, current evidence on OC DDIs, and the interpretation of PD end points are reviewed. With the emergence of new tools like physiologically based PK modeling, the decision to conduct an in vivo study can be made with much more confidence. This review provides a comprehensive overview of various factors that need to be considered in designing OC DDI studies and recommends PK-based DDI studies with PK end points as adequate measures to establish clinical drug interaction and measurement of PD end points when there is basis for PD interaction.

A Clinical Approach to Catamenial Epilepsy: A Review

IMPORTANCE

Catamenial epilepsy (CE) is exacerbated by hormonal fluctuations during the menstrual cycle. Approximately 1.7 million women have epilepsy in the United States. CE affects more than 40% of women with epilepsy. There is a paucity of literature addressing this condition from a clinical standpoint, and the literature that does exist is limited to the neurological community. This article reviews the diagnosis and management of CE for the non-neurologist. Women with CE have early touch points in their care with numerous health care providers before ever consulting with a specialist, including OB/GYNs, pediatricians, emergency department physicians, and family medicine providers. In addition, women affected by CE have seizures that are more recalcitrant to traditional epilepsy treatment regimens. To optimize management in patients affected by CE, menstrual physiology must be understood, individualized hormonal contraception treatment considered, and adjustments and interactions with antiepileptic drugs addressed.

OBSERVATIONS

CE is a unique subset of seizure disorders affected by menstrual fluctuations of progesterone and estrogen. The diagnosis of CE has been refined and clarified. There is an ever-increasing understanding of the importance and variety of options of hormonal contraception available to help manage CE. Furthermore, antiepileptic drugs and contraception can interact, so attention must be directed to optimizing both regimens to prevent uncontrolled seizures and pregnancy.

CONCLUSION AND RELEVANCE

CE can be diagnosed with charting of menstrual cycles and seizure activity. Hormonal treatments that induce amenorrhea have been shown to reduce CE. Optimizing antiepileptic drug dosing and contraceptive methods also can minimize unplanned pregnancies in women affected by CE.

ACOG Practice Bulletin No. 206: Use of Hormonal Contraception in Women With Coexisting Medical Conditions

Although numerous studies have addressed the safety and effectiveness of hormonal contraceptive use in healthy women, data regarding women with underlying medical conditions or other special circumstances are limited. The U.S. Medical Eligibility Criteria (USMEC) for Contraceptive Use, 2016 (), which has been endorsed by the American College of Obstetricians and Gynecologists, is a published guideline based on the best available evidence and expert opinion to help health care providers better care for women with chronic medical problems who need contraception. The goal of this Practice Bulletin is to explain how to use the USMEC rating system in clinical practice and to specifically discuss the rationale behind the ratings for various medical conditions. Contraception for women with human immunodeficiency virus (HIV) (); the use of emergency contraception in women with medical coexisting medical conditions, including obesity, (); and the effect of depot medroxyprogesterone acetate (DMPA) on bone health () are addressed in other documents from the American College of Obstetricians and Gynecologists.

The Impact of Gonadal Hormones on the Expression of Human Neurological Disorders

The effects of gonadal steroids on neurological well-being and disease constitute a rich and rapidly expanding area of basic and clinical neuroscience. Gonadal hormones exert potent effects on monoaminergic, cholinergic and peptidergic pathways as well as neurosteroidogenesis which, in turn, impact normal brain organization and function. A spectrum of human neurological conditions are influenced by hormonal fluctuations associated with the menstrual cycle, pregnancy, the menopause and use of oral contraceptives. An appreciation of these relationships may facilitate the development of specific hormonal and anti-hormonal therapies for neurological disorders as disparate as catamenial epilepsy and acute intermittent porphyria.

Drug interactions with the newer antiepileptic drugs (AEDs)--Part 2: pharmacokinetic and pharmacodynamic interactions between AEDs and drugs used to treat non-epilepsy disorders

Since antiepileptic drugs (AEDs) are prescribed to treat various non-epilepsy-related disorders in addition to the fact that patients with epilepsy may develop concurrent disorders that will need treatment, the propensity for AEDs to interact with non-AEDs is considerable and indeed can present a difficult clinical problem. The present review details the pharmacokinetic and pharmacodynamic interactions that have been reported to occur with the new AEDs (eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, pregabalin, retigabine (ezogabine), rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide) and drugs used to treat non-epilepsy disorders. Interaction study details are described, as necessary, so as to allow the reader to take a view as to the possible clinical significance of particular interactions. Pharmacokinetic interactions relate to hepatic enzyme induction or inhibition and involved a variety of drugs including psychoactive drugs, cardioactive drugs, oral contraceptives, antituberculous agents, analgesics and antineoplastic drugs. A total of 68 pharmacokinetic interactions have been described, with lamotrigine (n = 22), topiramate (n = 18) and oxcarbazepine (n = 7) being associated with most, whilst lacosamide, pregabalin, stiripentol and vigabatrin are associated with none. Overall, only three pharmacodynamic interactions have been described and occur with oxcarbazepine, perampanel and pregabalin.

[Antiepileptics in women of childbearing age and during pregnancy: comparison of specialized information with the current state of knowledge in Germany and Switzerland]

BACKGROUND

Healthcare professionals regularly read the summary of product characteristics (SmPC) as one of the various sources of information on the risks of drug use in women of childbearing age and during pregnancy. The aim of this article is to present an overview of the teratogenic potential of various antiepileptic drugs and to compare these data with the information provided by the SmPCs.

METHODS

A literature search on the teratogenic risks of 19 antiepileptic agents was conducted and the results were compared with the information on the use in women of childbearing age and during pregnancy provided by the SmPCs of 38 commercial products available in Switzerland and Germany.

RESULTS

The teratogenic risk is discussed in all available SmPCs. Quantification of the risk for birth defects and the numbers of documented pregnancies are mostly missing. Reproductive safety information in SmPCs showed poor concordance with risk levels reported in the literature. Recommendations concerning the need to monitor plasma levels and possibly perform dose adjustments during pregnancy to prevent treatment failure were missing in five Swiss and two German SmPCs.

DISCUSSION

The information regarding use in women of childbearing age and during pregnancy provided by the SmPCs is heterogeneous and poorly reflects the current state of knowledge. Regular updates of SmPCs are warranted in order for these documents to be of reliable use for health care professionals.

Clinical pharmacokinetic interactions between antiepileptic drugs and hormonal contraceptives

Contraceptive management in women with epilepsy is critical owing to the potential maternal and fetal risks if contraception or seizure management fails. This article briefly describes the pharmacokinetic interactions between antiepileptic drugs (AEDs) and hormonal contraceptives and the rational strategies that may overcome these risks. Hormonal contraception, including the use of oral contraceptives (OCs), is widely used in many women with epilepsy - there is no strong evidence of seizures worsening with their use. AEDs are the mainstay for seizure control in women with epilepsy. However, there are many factors to consider in the choice of AED therapy and hormonal contraception, since some AEDs can reduce the efficacy of OCs owing to pharmacokinetic interactions. Estrogens and progestogens are metabolized by cytochrome P450 3A4. AEDs, such as phenytoin, phenobarbital, carbamazepine, felbamate, topiramate, oxcarbazepine and primidone, induce cytochrome P450 3A4, leading to enhanced metabolism of either or both the estrogenic and progestogenic component of OCs, thereby reducing their efficacy in preventing pregnancy. OCs can also decrease the concentrations of AEDs such as lamotrigine and, thereby, increase the risk of seizures. Increased awareness of AED interactions may help optimize seizure therapy in women with epilepsy.

Women and epilepsy: review and practical recommendations

Individuals with epilepsy experience a number of sex-specific problems. In women, pregnancy and delivery are obvious issues, fertility problems are more often encountered and they also seem to have a higher frequency of sexual problems. A large number of women with epilepsy experience seizure exacerbation in relation to the menstrual cycle and have higher frequencies of menstrual disturbances and polycystic ovaries. Cosmetic problems affecting skin, hair or weight may also be drug induced. The use of antiepileptic drugs may influence the effect of contraceptives leading to unplanned pregnancies and contraceptives may affect the serum levels of antiepileptic drugs. The care of pregnant women with epilepsy requires attention to a number of guidelines and close cooperation between neurologist and gynecologist is recommended. Although the majority of the women with epilepsy experience normal pregnancies and deliveries, their children have a higher risk of birth defects. At menopause, their seizure pattern may change and some antiepileptic drugs may increase the risk of osteoporosis. The optimal treatment of women with epilepsy should take into account these gender-specific issues in the different stages of life.

Contraception and prenatal vitamin supplementation for women on antiepileptic medications

This article identifies interactions among AEDs with hormonal contraceptives and summarizes management strategies from the literature. Recommendations for addressing folate, vitamin K, and vitamin D deficiency caused by AEDs are also reviewed.

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.

Rapid and sensitive LC-MS/MS method for determination of felbamate in mouse plasma and tissues and human plasma

Felbamate (2-phenyl-1,3-propanediol dicarbamate) is a second generation antiepileptic drug used to treat seizures refractory to other antiepileptic drugs. With approximately 3500 new patients exposed annually, several important pharmacologic interaction questions remain unanswered necessitating the need for rapid and accurate methods of felbamate analysis in biological matrices. To this end, a rapid liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for the measurement of felbamate in mouse plasma and tissues and human plasma. Plasma (100 μL) and tissues homogenates (100 μL of 100 mg/mL) were spiked with internal standard (carisoprodol) prior to protein precipitation with acetonitrile. Samples were chromatographed on a XBridge Phenyl, 2.5 μm, 4.6 mm×50 mm column with quantitation by internal standard reference monitoring of the ion transitions m/z 239→117 for felbamate and m/z 261→176 for carisoprodol. Calibration curves were linear from 2.5 to 500 ng/mL in mouse or human plasma and 25-5000 pg/mg in tissue homogenates. Recoveries were greater than 97% for plasma and homogenates with accuracies >92% in any of the mouse matrices and >88% in human plasma. Comparable accuracies and precision were found with and without the use of the internal standard in preparation of the calibration curves and suggest that the internal standard may not be required.

[Therapeutic drug monitoring of felbamate]

Felbamate is a derivative of meprobamate used in second-line partial epilepsy and in the Lennox-Gastaut syndrome. Felbamate is well absorbed and has linear kinetics: C(max) and AUC increasing linearly with dose. The metabolism takes place in the liver. Metabolites represent 40 to 60% of excretion and are eliminated via the urine. The half-life is between 15 and 23 hours. Clearance is dependent on renal function. There is a concentration - efficacy and concentration - toxicity relationship. These arguments are in favour of a TDM but the therapeutic range is not clearly established. Potentially fatal side effects can be caused by felbamate (aplastic anemia, acute liver failure), which limits its use because they are dose-independant.

Selection of antiepileptic drugs in adults

Epilepsy affects approximately 50 million people worldwide, with an annual incidence of 50 to 70 cases per 100,000 population. The condition can strike at any time of life, with an immediate impact on everyday activities and routine. Key to optimal management is swift referral to an epilepsy specialist, appropriate investigation, and timely institution of antiepileptic drug therapy. In the past 20 years, the explosion of 13 new agents into the marketplace has greatly increased the potential for therapeutic intervention. This article explores the rationale for treatment selection in adults with epilepsy.

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.

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.

Application and interpretation of hPXR screening data: Validation of reporter signal requirements for prediction of clinically relevant CYP3A4 inducers

A human pregnane X receptor (PXR) reporter-gene assay was established and validated using 19 therapeutic agents known to be clinical CYP3A4 inducers, 5 clinical non-inducers, and 6 known inducers in human hepatocytes. The extent of CYP3A4 induction (measured as RIF ratio in comparison to rifampicin) and EC50 was obtained from the dose-response curve. All of the clinical inducers (19/19) and human hepatocyte inducers (6/6) showed positive responses in the PXR assay. One out of five clinical non-inducers, pioglitazone, also showed a positive response. An additional series of 18 commonly used drugs with no reports of clinical induction was also evaluated as putative negative controls. Sixteen of these were negative (89%), whereas two of these, flutamide and haloperidol showed 16-fold (RIF ratio 0.79) and 10-fold (RIF ratio 0.48) maximal induction, respectively in the reporter-gene system. Flutamide and haloperidol were further demonstrated to cause CYP3A4 induction in human cryopreserved hepatocytes based on testosterone 6beta-hydroxylation activity. The induction potential index calculated based on the maximum RIF ratio, EC50, and in vivo maximum plasma concentration was used to predict the likelihood of CYP3A4 induction in humans. When the induction potential index is greater than 0.08, the compound is likely to cause induction in humans. A high-throughput screening strategy was developed based on the validation results at 1microM and 10microM for the same set of drugs. A RIF ratio of 0.4 was set as more practical screening cut-off to minimize the possibility of generating false positives. Thus, a tiered approach was implemented to use the human PXR reporter-gene assay from early lead optimization to late lead characterization in drug discovery.

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.

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.

The pharmacokinetic and pharmacodynamic consequences of the co-administration of lamotrigine and a combined oral contraceptive in healthy female subjects

AIMS

To assess the pharmacokinetic and pharmacodynamic effects of co-administration of a combined oral contraceptive (ethinyloestradiol plus levonorgestrel) and lamotrigine.

METHODS

Over a period of 130 days, healthy female subjects took lamotrigine (titrated up to 300 mg day(-1)) and the combined oral contraceptive, either individually or as co-therapy. Plasma ethinyloestradiol and levonorgestrel concentrations were measured in the presence and absence of lamotrigine, and serum lamotrigine concentrations were measured in the presence and absence of the combined oral contraceptive. Serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), progesterone, oestradiol and sex hormone binding globulin were also determined.

RESULTS

Of the 22 enrolled subjects, 16 had evaluable pharmacokinetic data. The mean (90% CI) ratios of lamotrigine area under the concentration-time curve from 0 to 24 h (AUC(0,24 h)) and maximum observed concentration (C(max)) of lamotrigine when it was given with the combined oral contraceptive and during monotherapy were 0.48 (0.44, 0.53) and 0.61 (0.57, 0.66), respectively. Ethinyloestradiol pharmacokinetics were unchanged by lamotrigine, the mean combined oral contraceptive + lamotrigine : combined oral contraceptive alone ratios (90% CI) of the AUC(0,24 h) and C(max) of levonorgestrel were 0.81 (0.76, 0.86) and 0.88 (0.82, 0.93), respectively. FSH and LH concentrations were increased (by 4.7-fold and 3.4-fold, respectively) in the presence of lamotrigine, but the low serum progesterone concentrations suggested that suppression of ovulation was maintained. Intermenstrual bleeding was reported by 7/22 (32%) of subjects during co-administration of lamotrigine and combined oral contraceptive.

CONCLUSIONS

A clinically relevant pharmacokinetic interaction was observed during co-administration of a combined oral contraceptive and lamotrigine. A dosage adjustment for lamotrigine may need to be considered when these agents are co-administered. A modest decrease in the plasma concentration of levonorgestrel was also observed but there was no corresponding hormonal evidence of ovulation.

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.

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.

Anticonvulsant and antiretroviral interactions

OBJECTIVE

To evaluate the clinical significance of interactions between anticonvulsant and antiretroviral agents and provide recommendations regarding their concurrent use.

DATA SOURCES

A PubMed search (1966 to April 2003) was conducted using individual anticonvulsant and antiretroviral drug names and the following key search terms: anticonvulsant, antiepileptic, antiretroviral, protease inhibitor, and pharmacokinetic. Abstracts from scientific meetings that pertained to drug interactions were manually reviewed.

STUDY SELECTION AND DATA EXTRACTION

All articles identified by the PubMed search were examined. Articles and abstracts from scientific meetings with relevant information were included.

DATA SYNTHESIS

Six case reports were identified that describe interactions between anticonvulsant agents and protease inhibitors. In several reports, carbamazepine serum concentrations increased by approximately two- to threefold with concurrent ritonavir, resulting in carbamazepine-related toxicity. Carbamazepine was also associated with loss of viral suppression when combined with indinavir. Phenytoin serum concentrations were decreased with nelfinavir in a patient who developed recurrent seizures. The effect of ritonavir on phenytoin was variable; a 30% reduction in phenytoin serum concentration occurred in one patient, while no apparent change was observed in another. Interactions with nonnucleoside reverse-transcriptase inhibitors are poorly characterized because existing data involve concurrent protease inhibitor therapy. The utility of newer anticonvulsant agents is explored. Experience with newer anticonvulsant agents in 2 patients at our site is also described.

CONCLUSIONS

Limited data exist regarding interactions between anticonvulsant and antiretroviral agents. Valproic acid and newer anticonvulsant agents may provide useful alternatives to first-generation agents. Clinicians need to be diligent when monitoring for anticonvulsant-antiretroviral interactions because of the potential for toxicity, loss of seizure control, and incomplete viral suppression.

Clinical Pharmacokinetics of Thalidomide

Thalidomide is a racemic glutamic acid derivative approved in the US for erythema nodosum leprosum, a complication of leprosy. In addition, its use in various inflammatory and oncologic conditions is being investigated. Thalidomide interconverts between the (R)- and (S)-enantiomers in plasma, with protein binding of 55% and 65%, respectively. More than 90% of the absorbed drug is excreted in the urine and faeces within 48 hours. Thalidomide is minimally metabolised by the liver, but is spontaneously hydrolysed into numerous renally excreted products. After a single oral dose of thalidomide 200 mg (as the US-approved capsule formulation) in healthy volunteers, absorption is slow and extensive, resulting in a peak concentration (C(max)) of 1-2 mg/L at 3-4 hours after administration, absorption lag time of 30 minutes, total exposure (AUC( infinity )) of 18 mg. h/L, apparent elimination half-life of 6 hours and apparent systemic clearance of 10 L/h. Thalidomide pharmacokinetics are best described by a one-compartment model with first-order absorption and elimination. Because of the low solubility of the drug in the gastrointestinal tract, thalidomide exhibits absorption rate-limited pharmacokinetics (the 'flip-flop' phenomenon), with its elimination rate being faster than its absorption rate. The apparent elimination half-life of 6 hours therefore represents absorption, not elimination. The 'true' apparent volume of distribution was estimated to be 16L by use of the faster elimination-rate half-life. Multiple doses of thalidomide 200 mg/day over 21 days cause no change in the pharmacokinetics, with a steady-state C(max) (C(ss)(max)) of 1.2 mg/L. Simulation of 400 and 800 mg/day also shows no accumulation, with C(ss)(max) of 3.5 and 6.0 mg/L, respectively. Multiple-dose studies in cancer patients show pharmacokinetics comparable with those in healthy populations at similar dosages. Thalidomide exhibits a dose-proportional increase in AUC at doses from 50 to 400 mg. Because of the low solubility of thalidomide, C(max) is less than proportional to dose, and t(max) is prolonged with increasing dose. Age, sex and smoking have no effect on the pharmacokinetics of thalidomide, and the effect of food is minimal. Thalidomide does not alter the pharmacokinetics of oral contraceptives, and is also unlikely to interact with warfarin and grapefruit juice. Since thalidomide is mainly hydrolysed and passively excreted, its pharmacokinetics are not expected to change in patients with impaired liver or kidney function.

Clinically important drug interactions in epilepsy: interactions between antiepileptic drugs and other drugs

Antiepileptic drugs (AEDs) are commonly prescribed for long periods, up to a lifetime, and many patients will require treatment with other agents for the management of concomitant or intercurrent conditions. When two or more drugs are prescribed together, clinically important interactions can occur. Among old-generation AEDs, carbamazepine, phenytoin, phenobarbital, and primidone are potent inducers of hepatic enzymes, and decrease the plasma concentration of many psychotropic, immunosuppressant, antineoplastic, antimicrobial, and cardiovascular drugs, as well as oral contraceptive steroids. Most new generation AEDs do not have clinically important enzyme inducing effects. Other drugs can affect the pharmacokinetics of AEDs; examples include the stimulation of lamotrigine metabolism by oral contraceptive steroids and the inhibition of carbamazepine metabolism by certain macrolide antibiotics, antifungals, verapamil, diltiazem, and isoniazid. Careful monitoring of clinical response is recommended whenever a drug is added or removed from a patient's AED regimen.

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

PURPOSE

To study the pharmacokinetics of a combination oral contraceptive (OC) containing norethindrone and ethinyl estradiol during OC monotherapy, concomitant OC and topiramate (TPM) therapy, and concomitant OC and carbamazepine (CBZ) therapy in order to comparatively evaluate the pharmacokinetic interaction, which may cause contraceptive failure.

METHODS

This randomized, open-label, five-group study included two 28-day cycles. Five groups of female subjects received oral doses of ORTHO-NOVUM 1/35 alone (cycle 1) and then concomitant with TPM or CBZ (cycle 2). The treatment groups were group 1, TPM, 50 mg/day; group 2, TPM, 100 mg/day; group 3, TPM, 200 mg/day; group 4, TPM, 200 mg/day (obese women); and group 5, CBZ, 600 mg/day. Group 4 comprised obese women whose body mass index (BMI) was between 30 and 35 kg/m(2). The BMI of the remaining four groups was < or =27 kg/m2.

RESULTS

Coadministration of TPM at daily doses of 50, 100, and 200 mg (nonobese) and 200 mg (obese) nonsignificantly (p > 0.05) changed the mean area under the curve (AUC) of ethinyl estradiol by -12%, +5%, -11%, and -9%, respectively, compared with OC monotherapy. A similar nonsignificant difference was observed with the plasma levels and AUC values of norethindrone (p > 0.05). CBZ (600 mg/day) significantly (p < 0.05) decreased the AUC values of norethindrone and ethinyl estradiol by 58% and 42%, respectively, and increased their respective oral clearance by 69% and 127% (p < 0.05). Because CBZ induces CYP 3A-mediated and glucuronide conjugation metabolic pathways, the significant increase in the oral clearance of ethinyl estradiol and norethindrone was anticipated.

CONCLUSIONS

TPM, at daily doses of 50-200 mg, does not interact with an OC containing norethindrone and ethinyl estradiol. The lack of the TPM-OC interaction is notable when it is compared with the CBZ-OC interaction.

Epilepsy and women's health: family planning, bone health, menopause, and menstrual-related seizures

Epilepsy uniquely affects more than 1 million American women and girls. Health care providers must be aware of the specific concerns and issues regarding the different effects epilepsy has on male and female patients. Epilepsy and antiepileptic drugs substantially affect women's health in the areas of menstruation, contraception, sexual function, pregnancy, menopause, and bone health. Optimal care of women with epilepsy requires collaboration among neurologists, obstetrician-gynecologists, internists, family practitioners, genetic counselors, and nurse educators. This article reviews some areas of concern for women living with epilepsy.

St. John's wort and oral contraceptives: reasons for concern?

St. John's wort (Hypericum perforatum) is one of the best-selling herbal remedies in the United States. It has been implicated as an inducer of the P450 enzyme system, and as such, may cause increased metabolism of certain drugs, including oral contraceptives. Women using oral contraceptives have been warned against using St. John's wort. To date, there are some case reports but little clinical data demonstrating risk of contraceptive failure if they do. This article reviews available data and discusses theoretical reasons for concern about possible drug-herb interactions.

Treatment of epilepsy in women of reproductive age: pharmacokinetic considerations

Although epilepsy affects men and women equally, there are many women's health issues in epilepsy, especially for women of childbearing age. These issues, which include menstrual cycle influences on seizure activity (catamenial epilepsy), interactions of contraceptives with antiepileptic drugs (AEDs), pharmacokinetic changes during pregnancy, teratogenicity and the safety of breastfeeding, challenge both the woman with epilepsy and the many healthcare providers involved in her care. Although the information in the literature on women's issues in epilepsy has grown steeply in recent years, there are many examples showing that much work is yet to be done. The purpose of this article is to review these issues and describe practical considerations for women of childbearing age with epilepsy. The article addresses the established or "first-generation" AEDs (phenobarbital, phenytoin, primidone, carbamazepine, ethosuximide and valproic acid) and the "second-generation" AEDs (felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide). Although a relationship between hormones and seizure activity is present in many women, good treatment options for catamenial epilepsy remain elusive. Drug interactions between enzyme-inducing AEDs and contraceptives are well documented. Higher dosages of oral contraceptives or a second contraceptive method are suggested if women use an enzyme-inducing AED. Planned pregnancy and counselling before conception is crucial. This counselling should include, but is not limited to, folic acid supplementation, medication adherence, the risk of teratogenicity and the importance of prenatal care. AED dosage adjustments may be necessary during pregnancy and should be based on clinical symptoms, not entirely on serum drug concentrations. Many groups have turned their attention to women's issues in epilepsy and have developed clinical practice guidelines. Although the future holds promise in this area, many questions and the need for progress remain.

Interactions between antiepileptic drugs and hormonal contraception

An interaction between antiepileptic drugs (AEDs) and the combined oral contraceptive pill was first proposed when the dose of estradiol in the oral contraceptive pill was reduced from 100 to 50 microg. There was a higher incidence of breakthrough bleeding and contraceptive failure among women with epilepsy compared with women in general. Since then, interaction studies have been undertaken to look for possible interactions between AEDs and the combined oral contraceptive pill. Phenobarbital (phenobarbitone), phenytoin, carbamazepine, oxcarbazepine, felbamate and topiramate have been shown to increase the metabolism of ethinylestradiol and progestogens. Therefore, if a women is on one of the AEDs and wishes to take the oral contraceptive pill, she will need to take a preparation containing at least 50 microg of ethinylestradiol. Levonorgestrel implants are contraindicated in women receiving these AEDs because of cases of contraceptive failure. It is recommended that medroxyprogesterone injections be given every 10 rather than 12 weeks to women who are receiving AEDs that induce hepatic microsomal enzymes. There are no interactions between the combined oral contraceptive pill, progesterone-only pill, medroxyprogesterone injections or levonorgestrel implants and the AEDs valproic acid (sodium valproate), vigabatrin, lamotrigine, gabapentin, tiagabine, levetiracetam, zonisamide, ethosuximide and the benzodiazepines. Therefore, normal dose contraceptive preparations can be used in patients receiving these AEDs.

Levetiracetam does not alter the pharmacokinetics of an oral contraceptive in healthy women

PURPOSE

This study was designed to evaluate whether levetiracetam, a novel antiepileptic drug (AED), influences the pharmacokinetics of steroid oral contraceptives.

METHODS

During a run-in phase, 18 healthy female patients received an oral contraceptive containing ethinyl estradiol, 0.03 mg, and levonorgestrel, 0.15 mg, for the first 21 days of two consecutive menstrual cycles. In a subsequent double-blind, randomized, two-way crossover treatment phase, subjects received either levetiracetam, 500 mg, or placebo twice daily concomitant with the oral contraceptive. Plasma concentrations of ethinyl estradiol and levonorgestrel were measured on days 14 and 15 of the two treatment periods for the evaluation of the 24-h kinetic parameters, and an additional sample was collected on day 21 to determine the trough plasma concentrations. Serum progesterone and luteinizing hormone (LH) levels were determined on days 13, 14, 15, and 21 of each cycle of the treatment phase.

RESULTS

The plasma concentration-time curves and pharmacokinetic parameters of ethinyl estradiol and levonorgestrel were not statistically different during concomitant treatment with either levetiracetam or placebo. The ratios of the log-transformed geometric mean areas under the plasma concentration-time curves (AUCs), maximal (Cmax) and minimal (Cmin) plasma concentrations, and trough concentrations on day 21 (C21) ranged from 99.12 to 99.96% for ethinyl estradiol and from 97.13 to 99.41% for levonorgestrel. The 90% confidence intervals of these ratios were well within the 80 to 125% acceptance range for lack of interaction. Serum progesterone and LH concentrations were fairly constant during the run-in and treatment phases and remained markedly below their respective physiologic levels. Safety and menstrual-bleeding patterns were comparable during levetiracetam and placebo administration.

CONCLUSIONS

Levetiracetam does not affect the pharmacokinetics of an oral contraceptive containing ethinyl estradiol and levonorgestrel, and on the basis of serum progesterone and LH levels, it does not affect the contraceptive efficacy.

New antiepileptic drugs: review on drug interactions

During the Past decade, nine new antiepileptic drugs (AEDs) namely, Felbamate, Gabapentin, Levetiracetam, Lamotrigine, Oxcarbazepine, Tiagabine, Topiramate, Vigabatrin and Zonisamide have been marketed worldwide. The introduction of these drugs increased appreciably the number of therapeutic combinations used in the treatment of epilepsy and with it, the risk of drug interactions. In general, these newer antiepileptic drugs exhibit a lower potential for drug interactions than the classic AEDs, like phenytoin, carbamazepine and valproic acid, mostly because of their pharmacokinetic characteristics. For example, vigabatrin, levetiracetam and gabapentin, exhibit few or no interactions with other AEDs. Felbamate, tiagabine, topiramate and zonisamide are sensitive to induction by known anticonvulsants with inducing effects but are less vulnerable to inhibition by common drug inhibitors. Felbamate, topiramate and oxcarbazepine are mild inducers and may affect the disposition of oral contraceptives with a risk of failure of contraception. These drugs also inhibit CYP2C19 and may affect the disposition of phenytoin. Lamotrigine is eliminated mostly by glucuronidation and is susceptible to inhibition by valproic acid and induction by classic AEDs such as phenytoin, carbamazepine, phenobarbital and primidone.

Treatment issues for women with epilepsy

Epilepsy affects over one percent of the population, including nearly one million women of childbearing potential. Women with epilepsy represent a particularly challenging group for neurologists and other health care professionals. Affected women are unaware of many of the unique issues they face, including the relationship between antiepileptic drug therapy and contraception, the risk of abnormal pregnancy outcomes, the effect of hormones and aging on seizure control, and the increased incidence of reproductive dysfunction. Worldwide educational efforts are underway to educate women and their physicians of these deficiencies.

Injectable contraception. New and existing options

DMPA and MPA/E2C contraception offer women safe, effective, convenient, and reversible birth control choices. The use of DMPA, a 3-month injectable, is characteristically associated with amenorrhea. Lactating women and women in whom contraceptive doses of estrogen are contraindicated can use this progestin-only birth control method. Return of fertility can be delayed in women discontinuing DMPA to become pregnant. In some cases, the use of DMPA also confers important noncontraceptive and therapeutic benefits. A monthly estrogen/progestin injectable contraceptive, MPA/E2C should appeal to women who are concerned about daily pill taking, who prefer regular cycles to amenorrhea, and who find monthly injections acceptable and accessible. As is true for oral contraceptives, MPA/E2C represents an appropriate choice for women who prefer a rapidly reversible contraceptive. Currently, the proposed contraindications for MPA/E2C parallel those for combined oral contraceptives. As MPA/E2C contraception becomes available for American women, clinicians will learn how to best include this new method among the array of contraceptive choices. By individualizing contraceptive selection, counseling, and management approaches based on the relevant behavioral and medical considerations reviewed herein, clinicians can maximize their patients' success with injectable contraceptives. The more innovative that clinicians, family planning agencies, and insurers are in facilitating access to care (including reinjections), the more women will be able to avail themselves of safe, effective, and reversible methods of contraception. In addition to the physician's office or health clinic, other sites at which women might receive contraceptive injections include employee health clinics, college health clinics, or perhaps the pharmacy where the prescription is filled. Self-administration may become an appropriate option for some users of injectable contraception.

Enzyme induction and inhibition by new antiepileptic drugs: a review of human studies

The aim of this paper is to review a number of new antiepileptic agents (i.e. felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide) for their inducing and/or inhibitory properties in humans, mainly considering the interactions where they are involved as the cause rather than the object of such interactions. Two aspects have been particularly taken into account: the changes or absence of changes in plasma/serum concentrations of concomitant drugs and the direct or indirect evidence of induction, inhibition or lack of effect on the six major human hepatic CYP isozymes (CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4), as well as on other CYP isozymes or enzyme systems. Felbamate clearly affects the pharmacokinetics of a number of drugs, generally increasing but also decreasing their concentrations. It induces enzymes such as CYP3A4 and inhibits enzymes such as CYP2C19 and those of the beta-oxidation pathway. Topiramate is not devoid of potential interaction properties: it decreases the plasma concentrations of ethinylestradiol, induces CYP3A4 and inhibits CYP2C19. For oxcarbazepine, no inhibitory, only inductive effects have been observed thus far. Felbamate. topiramate and oxcarbazepine may induce the metabolism of steroidal oral contraceptives. In this respect, tiagabine has been studied at a rather low dose. Pharmacodynamic or pharmacokinetic interaction seems to exist between lamotrigine and carbamazepine. Lamotrigine appears to be a weak inducer of UGTs, whereas induction of CYP3A4 seems improbable as the compound does not change the concentrations of oral contraceptives or the urinary excretion of 6beta-hydroxycortisol. Zonisamide has very peculiar pharmacokinetics and an extensive metabolism. Additional information on its enzyme inducing or inhibiting properties would be necessary, as data so far collected on its effect on the pharmacokinetics of other drugs are conflicting. Gabapentin, vigabatrin and in particular levetiracetam appear to be devoid of significant enzyme inducing or inhibiting properties.

Pharmacokinetic drug interactions between oral contraceptives and second-generation anticonvulsants

Drug interactions between oral contraceptives (OCs) and traditional anticonvulsants have been well described. However, in the past decade, a number of new anticonvulsants have been developed, as well as modifications made in the composition of the OC preparations themselves. Additionally, anticonvulsants are increasingly employed in the therapy of nonseizure-related disorders, placing more women at risk of potential drug interactions that may lead to contraceptive failure. Second-generation anticonvulsants include felbamate, gabapentin, lamotrigine, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide. Most have been approved for adjunctive management of seizures refractory to therapy with traditional anticonvulsants. On the basis of available study data in women receiving concomitant OC preparations, gabapentin, lamotrigine, tiagabine and vigabatrin may be administered without significant pharmacokinetic interactions that potentially diminish contraceptive efficacy. However, additional or alternative contraceptive measures, including using OCs with higher estrogen content, are recommended when using felbamate, oxcarbazepine and topiramate, as these agents have demonstrated enzyme-inducing activity leading to reduced plasma steroid concentrations. The effects of zonisamide in women receiving OCs have yet to be reported. It is important to characterise the properties [e.g. substrate and enzyme activity (particularly cytochrome P450 3A4 induction)] of new anticonvulsants and recognise their potential to interfere with OCs. However, a pharmacokinetic interaction does not in itself indicate loss of OC efficacy. Contraceptive failure should be measured by changes in ovarian hormone concentrations, maturation of ovarian follicle(s) or ovulation.

The clinical pharmacokinetics of the new antiepileptic drugs

Because pharmacokinetics is a major determinant of the magnitude and duration of pharmacologic response, understanding the kinetic properties of the new antiepileptic drugs (AEDs) is essential for the correct use of these compounds in clinical practice. After oral administration, absorption is rapid and relatively efficient for the new AEDs, the most notable exception being gabapentin, whose bioavailability decreases with increasing dosage. None of the new AEDs is extensively bound to plasma proteins except for tiagabine, which is over 95% protein-bound. The route of elimination differs to an important extent from one compound to another, and elimination half-lives range from over 30 h for zonisamide to 5-7 h for gabapentin. For all drugs that are metabolized, half-life is shortened and clearance is increased when patients receive concomitant enzyme-inducing agents such as barbiturates, phenytoin, and carbamazepine. Lamotrigine metabolism is markedly inhibited by valproic acid, and felbamate may increase the serum levels of most other AEDs. Felbamate, topiramate, and oxcarbazepine may also reduce the efficacy of the contraceptive pill by stimulating its metabolism.

Pharmacotherapeutic issues for women of childbearing age with epilepsy

OBJECTIVE

To provide an overview of key pharmacotherapeutic issues in epilepsy for the woman of childbearing potential.

DATA SOURCES

A MEDLINE search (1966-1997) was done to identify pertinent literature. Chapters in epilepsy textbooks, pregnancy registries, and their respective bibliographies were also evaluated.

STUDY SELECTION AND DATA EXTRACTION

All identifiable sources written in English were evaluated.

DATA SYNTHESIS

Epilepsy is a common neurologic disorder. It is estimated that nearly 1 million American women of childbearing age have epilepsy. There are many women's health issues in epilepsy. These include menstrual cycle influences on seizure activity, contraceptive-antiepileptic drug interactions, pharmacokinetic changes during pregnancy, teratogenicity of antiepileptic drugs, breast-feeding, and quality of life. These issues challenge both the woman with epilepsy and the many healthcare providers involved in her care. This article reviews these issues and makes recommendations. It addresses both the first-generation antiepileptic drugs (phenobarbital, phenytoin, carbamazepine, valproic acid) and the newer or second-generation agents (felbamate, gabapentin, lamotrigine, topiramate, tiagabine).

CONCLUSIONS/RECOMMENDATIONS

Drug interactions between enzyme-inducing antiepileptic drugs and contraceptives are well documented. Higher doses of oral contraceptives or a second contraceptive method are suggested if epileptic women use an enzyme-inducing antiepileptic drug. Planned pregnancy is highly recommended and counseling before conception is crucial. Prepregnancy counseling should include, but is not limited to, folic acid supplementation, optimal control of seizure activity, monotherapy with the lowest effective antiepileptic drug dose, and medication adherence. Patient information should be provided about the risk of teratogenicity and the importance of prenatal care. Antiepileptic drug dosage adjustments may be necessary and should be based on clinical symptoms, not solely on serum drug concentrations. While the future holds promise for many aforementioned women's issues in epilepsy, many questions remain to be answered.

Evaluation of the potential interaction between felbamate and erythromycin in patients with epilepsy

Effects of erythromycin on hepatic CYP450 3A4 isozymes can profoundly influence the metabolism of many therapeutic agents. An open-label, randomized, two-period, crossover study was therefore conducted to evaluate the pharmacokinetics of felbamate before and after a concurrent 10-day regimen (333 mg three times daily) of erythromycin. Patients were receiving either 3,000 or 3,600 mg/day felbamate monotherapy for treatment of epilepsy. Mean dose-normalized values for maximum concentration (Cmax) and area under the concentration-time curve (AUC tau) of felbamate were not statistically different in patients taking felbamate as monotherapy than in patients after erythromycin coadministration. Estimates of time to Cmax (tmax), minimum concentration (Cmin), apparent clearance (Cl/kg), average concentration (Cav), and degree of fluctuation (DFss) were likewise unchanged. The incidence of mild and moderate adverse events increased during coadministration of the two drugs. Because patients with epilepsy can not be treated with erythromycin alone, it could not be determined whether the adverse events were attributable to erythromycin or to the combination of the two drugs. Steady-state pharmacokinetic parameters of felbamate were not influenced by erythromycin coadministration.