Clinically relevant drug interactions with antiepileptic drugs

The efficacy of gabapentin in children of partial seizures and the blood levels

AIM

To evaluate the long-term efficacy of gabapentin (GBP) and usefulness of measurement of the blood level for the observation of patients that have partial seizures.

METHODS

Thirty patients (20 effective cases and 10 ineffective cases) treated with GBP for the localization related epilepsy had their peak blood levels of GBP. The levels were measured seven time points, one, 6, 12, 18, 24, 30, and 36month after the start of medication. The efficacy of GBP was evaluated at one month after the initiation of medication and every year for 3years, based on the R Ratio and the degree of improvement for the paroxysmal strength and length.

RESULTS

GBP levels were higher in the effective cases than the levels in the ineffective cases 6months after and 1year after the initiation of medication (p<0.05). The level 6months after the start in the effective cases was 5.429±2.384μg/ml (mean±SD), and 5.837±3.217μg/ml after 1year. The cases that were effective for 1year maintained approximately the same efficacy for 3years after the initiation of medication, but there was no correlation between the level and the R Ratio, paroxysmal strength and length.

CONCLUSIONS

No precise definition of the therapeutic range was recognized because of no correlation between GBP level and the improvement of clinical manifestations. We recommend the GBP optimal range that is established the range within 3-8μg/ml (mean; 5μg/ml) as therapeutic target without the side effect.

Optimizing antiepileptic drug treatment in tumoral epilepsy

Between 30% and 50% of patients with brain tumors first present with a seizure, and up to 30% more will develop seizures later. Therefore, optimal management of these patients requires a rational approach to the use of antiseizure medications. Based on current evidence, prophylactic prescription of long-term antiepileptic drugs (AEDs) in patients with brain tumors in patients who did not present with seizures is not justified. Because of the high risk of recurrence, however, AED treatment should be strongly considered after a single seizure considered to be due to a tumor. Because of the lack of well-controlled randomized trials, the decision on which AED provides the best risk-benefit ratio in the individual patient is based mostly on physician's judgment rather than sound scientific evidence. In patients who may require chemotherapy, a non-enzyme-inducing AED is preferred for initial treatment to minimize the risk of drug interactions that impact adversely on the outcome of anticancer chemotherapy. Several retrospective studies in seizure patients with glioblastoma treated with chemotherapy have provided evidence for a moderately improved survival with the use of valproic acid, possibly due to inhibition of histone deacetylase. However, valproic acid may also increase the hematologic toxicity of antineoplastic drugs, presumably by inhibiting their metabolism, and may independently impair hemostasis, which is of some concern for patients who require surgical intervention. Among newer generation AEDs, levetiracetam has a number of advantageous features, including availability of a parenteral formulation, but other agents such as gabapentin, lamotrigine, oxcarbazepine, topiramate, and zonisamide may also be considered. Potentially more effective treatments targeting specific mechanisms of epileptogenesis and ictogenesis are being investigated. Resection of the tumor, radiation therapy, or chemotherapy can bring refractory seizures under control or prolong the duration of seizure freedom, an effect that does not appear to be necessarily related to removal or shrinkage of the tumor mass. In patients with a successfully treated tumor and an overall good prognosis for long-term survival, gradual discontinuation of AEDs may be considered.

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.

What are the arguments for and against rational therapy for epilepsy?

Although more than a dozen new anti-seizure drugs (ASDs) have entered the market since 1993, a substantial proportion of patients (~30 %) remain refractory to current treatments. Thus, a concerted effort to identify and develop new therapies that will help these patients continues. Until this effort succeeds, it is reasonable to re-assess the use of currently available therapies and to consider how these therapies might be utilized in a more efficacious manner. This applies to the selection of monotherapies in newly-diagnosed epilepsy, but perhaps, more importantly, to the choice of combination treatments in otherwise drug-refractory epilepsy. Rational polytherapy is a concept that is predicated on the combination of drugs with complementary mechanisms of action (MoAs) that work synergistically to maximize efficacy and minimize the potential for adverse events. Furthermore, rational polytherapy requires a detailed understanding of the MoA subclasses amongst available ASDs and an appreciation of the empirical evidence that supports the use of specific combinations. The majority of ASDs can be loosely categorized into those that target neurotransmission and network hyperexcitability, modulate intrinsic neuronal properties through ion channels, or possess broad-spectrum efficacy as a result of multiple mechanisms. Within each of these categories, there are discrete pharmacological profiles that differentiate individual ASDs. This chapter will consider how knowledge of MoA can help guide therapy in a rational manner, both in the selection of monotherapies for specific seizure types and syndromes, but also in the choice of drug combinations for patients whose epilepsy is not optimally controlled with a single ASD.

Drug Interaction Between Phenytoin and Valproic Acid in a Child With Refractory Epilepsy

Introduction:

There are no published reports on pediatric phenytoin toxicity, resulting from the drug interaction between phenytoin and valproic acid.

Case description:

A 12-year-old patient with refractory epilepsy syndrome presented with phenytoin toxicity, following a concomitant treatment with phenytoin, valproic acid, and lamotrigine. The phenytoin concentration detected in the capsules used by the patient was in accordance with the prescribed dose and was appropriate for the age and weight of the patient. However, a supratherapeutic phenytoin serum concentration was observed (21.92 µg phenytoin/mL of blood). Consequently, the phenytoin dose was reduced, and the patient was monitored; 24 hours later the patient did not present with any signs/symptoms of toxicity.

Discussion:

Despite the appropriate phenytoin concentration in the capsules, the patient presented with phenytoin toxicity. This toxicity likely resulted from the drug interaction between phenytoin and valproic acid that leads to phenytoin displacement from plasmatic proteins and inhibits phenytoin metabolism, thereby increasing the concentration of free drug in the serum.

Safety and tolerability of different titration rates of retigabine (ezogabine) in patients with partial-onset seizures

Retigabine (RTG; international nonproprietary name)/ezogabine (EZG; US adopted name) is an antiepileptic drug (AED) that prolongs neuronal voltage-gated potassium-channel KCNQ2-5 (Kv 7.2-7.5) opening. This double-blind study evaluated different RTG/EZG dose-titration rates. Patients (N=73) with partial-onset seizures receiving concomitant AEDs were randomized to one of three titration groups, all of which were initiated at RTG/EZG 300mg/day divided into three equal doses. Fast-, medium-, and slow-titration groups received dose increments of 150mg/day every 2, 4, and 7 days, respectively, achieving the target dose of 1200mg/day after 13, 25, and 43 days, respectively. Safety assessments were performed throughout. Discontinuation rates due to treatment-emergent adverse events (TEAEs) were numerically higher in the fast- (10/23) and medium- (7/22) titration groups than in the slow-titration group (3/23) but statistical significance was achieved only for the high-titration group compared with the low-titration group (p=0.024). Stratified analysis, with concomitant AEDs divided into enzyme inducers (carbamazepine, phenytoin, oxcarbazepine) or noninducers, showed that the risk of discontinuation due primarily to TEAEs was significantly higher in the fast- (p=0.010) but not in the medium-titration group (p=0.078) when compared with the slow-titration group. Overall, the slow-titration rate appeared to be best tolerated and was used in further efficacy and safety studies with RTG/EZG.

Management of the elderly patients with inflammatory bowel disease: practical considerations

The aging U.S. population will approach 20% of the total population by 2030. The number of older patients with inflammatory bowel disease is anticipated to increase accordingly bringing the burden of multiple comorbidities, polypharmacy with drug interactions, the aging immune system, and extended social and financial issues to overall management of an already challenging management of these patients. Each of these concerns is measured by the metric of distinguishing the "fit versus frail" elderly and will be discussed in this review with an emphasis on a practical guide to therapy.

Interaction of carbamazepine with herbs, dietary supplements, and food: a systematic review

Background. Carbamazepine (CBZ) is a first-line antiepileptic drug which may be prone to drug interactions. Systematic review of herb- and food-drug interactions on CBZ is warranted to provide guidance for medical professionals when prescribing CBZ. Method. A systematic review was conducted on six English databases and four Chinese databases. Results. 196 out of 3179 articles fulfilled inclusion criteria, of which 74 articles were reviewed and 33 herbal products/dietary supplement/food interacting with CBZ were identified. No fatal or severe interactions were documented. The majority of the interactions were pharmacokinetic-based (80%). Traditional Chinese medicine accounted for most of the interactions (n = 17), followed by food (n = 10), dietary supplements (n = 3), and other herbs/botanicals (n = 3). Coadministration of 11 and 12 of the studied herbal products/dietary supplement/food significantly decreased or increased the plasma concentrations of CBZ. Regarding pharmacodynamic interaction, Xiao-yao-san, melatonin, and alcohol increased the side effects of CBZ while caffeine lowered the antiepileptic efficacy of CBZ. Conclusion. This review provides a comprehensive summary of the documented interactions between CBZ and herbal products/food/dietary supplements which assists healthcare professionals to identify potential herb-drug and food-drug interactions, thereby preventing potential adverse events and improving patients' therapeutic outcomes when prescribing CBZ.

Safe Treatment of Seizures in the Setting of HIV/AIDS

OPINION STATEMENT

HIV(+) patients are at increased risk for developing seizures due to the vulnerability of the central nervous system to HIV-associated diseases, immune dysfunction, and metabolic disturbances. In patients with acute seizures, standard protocols still apply with urgent seizure cessation being the priority. Management of the person with established epilepsy who contracts HIV is challenging, but the decision to initiate chronic antiepileptic drug (AED) therapy in an HIV(+) patient is also difficult. Chronic treatment guidelines emphasize the interactions between AEDs and antiretroviral (ARV) medications, but provide no explicit advice regarding when to initiate an AED, what medication to select, and/or the duration of treatment. Epidemiologic data regarding seizure recurrence risk in HIV(+) individuals is not available. The risk of further seizures likely depends upon the underlying etiology for the seizure(s) and patients' immune status and may be increased by the use of efavirenz (an ARV). The issues for consideration include AED-ARV interactions, organ dysfunction, seizure type, and drug side effects, which may worsen or be confused with symptoms of HIV and/or epilepsy. Co-administration of enzyme inducing (EI)-AEDs and ARVs can result in virological failure, breakthrough seizure activity, AED toxicity, and/or ARV toxicity. Where available, the AED of choice in HIV(+) patients is levetiracetam due to its broad spectrum activity, ease of use, minimal drug interactions, and favorable side effect profile. Lacosamide, gabapentin, and pregabalin are also favored choices in patients with partial onset seizures and/or those failing levetiracetam. Where newer AEDs are not available, valproic acid may be the treatment of choice in terms of an AED, which will not cause enzyme induction-associated ARV failure, but its side effect profile causes other obvious problems. In resource-limited settings (RLS) where only EI-AEDs are available, there are no good treatment options and further pressure needs to be placed upon policymakers to address this care gap and public health threat.

Interaction of valproic acid and amitriptyline: analysis of therapeutic drug monitoring data under naturalistic conditions

Amitriptyline (AMI) and valproic acid (VPA) are common psychotropic drugs which are frequently used in psychiatry and also administered in neurology or anesthesia in the absence of a psychiatric indication. On the basis of the case of a 73-year-old man with therapy-resistant major depressive episode who experienced anticholinergic delirium after adding VPA to AMI, we retrospectively analyzed therapeutic drug monitoring data of the years 2008 to 2010. We assessed cases receiving a combination of AMI and VPA, and obtained a control sample of AMI patients without VPA which were matched for sex, age, daily dose, and comedication. Both samples were compared regarding the serum levels of AMI and nortriptyline (NOR) as well as the ratio of NOR and AMI with the Mann-Whitney U test. The combination of AMI and VPA led to a remarkable increase of AMI and NOR serum levels. When comparing 33 patients who received comedication with VPA versus 33 matched controls, the total concentration by combining mean AMI and NOR serum levels (237.1 [119.9] vs 126.4 [52.8] ng/mL) and NOR/AMI ratio (1.300 [0.905] vs 0.865 [0.455]) was significantly higher. Both AMI and VPA are widely prescribed drugs. A combination of both is common for psychiatric or neurologic patients. A cautious dosing of AMI with VPA comedication is advisable, and therapeutic drug monitoring should be performed because this combination may lead to a remarkable increase of AMI and NOR serum levels.

Risk of ischemic cerebrovascular and coronary events in adult users of anticonvulsant medications in routine care settings

Background

Older‐generation anticonvulsants that highly induce cytochrome P450 enzyme system activity produce metabolic abnormalities that may increase cardiovascular risk. The objective of this study was to evaluate the risk of ischemic cerebrovascular and coronary events in adult new users of anticonvulsants that highly induce cytochrome P450 activity compared with other anticonvulsant agents, as observed in a routine care setting.

Methods and Results

This was a cohort study of patients 40 to 64 years old from the HealthCore Integrated Research Database who had initiated an anticonvulsant medication between 2001 and 2006 and had no recorded major coronary or cerebrovascular condition in the 6 months before treatment initiation. Propensity score (PS) matching was used to evaluate ischemic cerebrovascular and coronary risk among anticonvulsant new users. High‐dimensional propensity score (hdPS)–matched analyses were used to confirm adjusted findings. The study identified 913 events in 166 031 unmatched new treatment episodes with anticonvulsant drugs. In a PS‐matched population of 22 864 treatment episodes, the rate ratio (RR) for ischemic coronary or cerebrovascular events associated with highly inducing agents versus other agents was 1.22 (95% CI, 0.90‐1.65). The RR moved to 0.99 (95% CI, 0.73‐1.33) with adjustment for hdPS matching (RR, 1.47; 95% CI, 0.95‐2.28 for cerebrovascular events; RR, 0.70; 95% CI, 0.47‐1.05 for coronary events).

Conclusions

In this exploratory analysis, there was no evidence of a consistent and statistically significant effect of initiating anticonvulsants that highly induce cytochrome P450 activity on ischemic coronary or cerebrovascular outcomes compared with other agents, given routine care utilization patterns.

Clinical pharmacology profile of vorinostat, a histone deacetylase inhibitor

PURPOSE

Vorinostat is a histone deacetylase inhibitor that has demonstrated preclinical activity in numerous cancer models. Clinical activity has been demonstrated in patients with a variety of malignancies. Vorinostat is presently indicated for the treatment of patients with advanced cutaneous T cell lymphoma (CTCL). Clinical investigation is ongoing for therapy of other solid tumors and hematological malignancies either as monotherapy or in combination with other chemotherapeutic agents. This review summarizes the pharmacokinetic properties of vorinostat.

METHODS

Monotherapy pharmacokinetic data across a number of pharmacokinetic studies were reviewed, and data are presented. In addition, literature review was performed to obtain published Phase I and II pharmacokinetic combination therapy data to identify and characterize potential drug interactions with vorinostat. Pharmacokinetic data in special populations were also reviewed.

RESULTS

The clinical pharmacology profile of vorinostat is favorable, exhibiting dose-proportional pharmacokinetics and modest food effect. There appear to be no major differences in the pharmacokinetics of vorinostat in special populations, including varying demographics and hepatic dysfunction. Combination therapy pharmacokinetic data indicate that vorinostat has a low propensity for drug interactions.

CONCLUSIONS

Vorinostat's favorable clinical pharmacology and drug interaction profile aid in the ease of administration of vorinostat for the treatment of advanced CTCL and will be beneficial in continued assessment for other oncologic indications. Although a number of studies have been conducted to elucidate the detailed pharmacokinetic profile of vorinostat, more rigorous assessment of vorinostat pharmacokinetics, including clinical drug interaction studies, will be informative.

Phenotypic interaction of simultaneously administered isoniazid and phenytoin in patients with tuberculous meningitis or tuberculoma having seizures

Treatment of tuberculous meningitis or tuberculoma has become complicated because of adverse drug interactions found amongst antitubercular and anticonvulsant drugs. The aim of the study is to evaluate the effect of simultaneously administered isoniazid (300 mg/day) and phenytoin (300 mg/day) on 60 patients with tuberculous meningitis or tuberculoma having seizures. Plasma samples were analyzed for isoniazid, acetylated-isoniazid (AcINH) and phenytoin levels by high performance liquid chromatography at 3h of drugs administration and patients were classified as rapid or slow acetylator on the basis of metabolic ratio of isoniazid (Rm) and percentage of acetylated-isoniazid (%AcINH). Out of 60 patients studied, 23 were slow acetylators and 37 were rapid acetylators. Slow acetylators revealed higher plasma isoniazid levels and lower plasma AcINH levels, metabolic ratio and %AcINH as compared to rapid acetylators. Plasma phenytoin levels were found to be significantly higher (above therapeutic range) in slow acetylators as compared to rapid acetylators. Plasma phenytoin concentration was moderately strong, negatively correlated with metabolic ratio (r=-0.439, P<0.001) and %AcINH (r=-0.729, P<0.001). Eight comatose patients (34.8%) also showed significantly higher plasma phenytoin levels. Our results suggest that assessment of acetylator status and plasma phenytoin level is critical for dose optimization of isoniazid and phenytoin and to predict the patients at risk of intoxication.

Adverse drug reactions to gabapentin and pregabalin: a review of the French pharmacovigilance database

BACKGROUND

Gabapentin and pregabalin are widely used as antineuropathic pain drugs. Their use is also associated with the development of adverse drug reactions (ADRs), mainly neuropsychiatric.

OBJECTIVE

The aim of this work was to study 'serious' and/or 'unexpected' adverse reactions associated with pregabalin and gabapentin.

STUDY DESIGN

We studied ADRs reported to the French Pharmacovigilance System occurring between 1995 and 2009.

MAIN OUTCOME MEASURE

For each ADR associated with gabapentin or pregabalin, we noted year, patient age and sex, type of adverse reaction, as well as the imputability score. Reporting rate of serious ADRs for gabapentin and pregabalin was estimated with regard to data of use (obtained from the French National Health Insurance Fund) using the defined daily dose. A global and descriptive analysis of the adverse reactions for each drug is presented. Secondly, details of deaths and ADRs with an imputability score of at least 'probable' or 'likely' were presented.

RESULTS

Overall, 1333 cases were recorded (725 related to gabapentin, 608 related to pregabalin), mainly neuropsychiatric ADRs. Among the 22 deaths recorded, 8 were related to gabapentin in obstetrical situations. Other less well-documented ADRs were identified, such as hepatitis associated with gabapentin and haematological ADRs associated with pregabalin.

CONCLUSION

This study confirmed the prevalence of neuropsychiatric ADRs associated with gabapentin or pregabalin. A high rate of death occurred with gabapentin in an obstetrical context. New adverse reactions have been noted, such as haematological or hepatic adverse reactions associated with pregabalin and gabapentin, respectively.

When one plus one makes three: the quest for rational antiepileptic polytherapy with supraadditive anticonvulsant efficacy

The experimental and clinical evidence in support of "rational polytherapy" is sparse, and to date, no clear evidence-based indications can be made to help physicians in their choice of a specific drug combination against specific forms of epilepsy. This article briefly reviews the data available in the literature and obtained from studies conducted in humans to evaluate which main AED combinations might possess supraadditive, synergistic effects in terms of efficacy, with infraadditive toxicity. By far, the most documented association resulting in supraadditive anticonvulsant effects against focal seizures is that of VPA and LTG. There are some indications that combinations of drugs with different primary mechanisms of action may be more effective than combining drugs with the same mechanisms of action. However, further animal and human research studies that focus both on toxicity and anticonvulsant effects of various combinations of AEDs are required.

Antioxidant, anticonvulsive and neuroprotective effects of dapsone and phenobarbital against kainic acid-induced damage in rats

Excitotoxicity due to glutamate receptors (GluRs) overactivation is a leading mechanism of oxidative damage and neuronal death in various diseases. We have shown that dapsone (DDS) was able to reduce both neurotoxicity and seizures associated to the administration of kainic acid (KA), an agonist acting on AMPA/KA receptors (GluK1-GluK5). Recently, it has been shown that phenobarbital (PB) is also able to reduce epileptic activity evoked by that receptor. In the present study, we tested the antioxidative, anticonvulsive and neuroprotective effects of DDS and PB administered alone or in combination upon KA toxicity to rats. Results showed that KA increased lipid peroxidation and diminished reduced glutathione (GSH), 24 h after KA administration and both drugs in combination or individually inhibited these events. Likewise, KA promotes mortality and this event was antagonized by effect of both treatments. Additionally, the behavioral evaluation showed that DDS and PB administered alone or in combination decreased the number of limbic seizures and reduced the percentage of animals showing tonic-clonic seizures versus the control group, which was administered only with KA. Finally, our study demonstrated that all of the treatments prevented the neuronal death of the pyramidal cell layer of hippocampal CA-3. In conclusion, the treatment with DDS and PB administrated alone or in combination exerted antioxidant, anticonvulsive and neuroprotective effects against the neurotoxicity induced by KA in rats, but their effects were not additive. Thus, it may be good options of treatment in diseases such as epilepsy and status epilepicus, administered separately.

Lack of effect of lacosamide on the pharmacokinetic and pharmacodynamic profiles of warfarin

PURPOSE

The aim of this study was to evaluate the effect of the antiepileptic drug lacosamide on the pharmacokinetics and pharmacodynamics of the anticoagulant warfarin.

METHODS

In this open-label, two-treatment crossover study, 16 healthy adult male volunteers were randomized to receive a single 25-mg dose of warfarin alone in one period and lacosamide 200 mg twice daily on days 1-9 with a single 25 mg dose of warfarin coadministered on day 3 in the other period. There was a 2-week washout between treatments. Pharmacokinetic end points were area under the plasma concentration-time curve (AUC(0,last) and AUC(0,∞) ) and maximum plasma concentration (Cmax ) for S- and R-warfarin. Pharmacodynamic end points were area under the international normalized ratio (INR)-time curve (AUCINR ), maximum INR (INRmax ), maximum prothrombin time (PTmax ) and area under the PT-time curve (AUCPT ).

KEY FINDINGS

Following warfarin and lacosamide coadministration, Cmax and AUC of S- and R-warfarin, as well as peak value and AUC of PT and INR, were equivalent to those after warfarin alone. In particular, the AUC(0,∞) ratio (90% confidence interval) for coadministration of warfarin and lacosamide versus warfarin alone was 0.97 (0.94-1.00) for S-warfarin and 1.05 (1.02-1.09) for R-warfarin, and the AUCINR ratio was 1.04 (1.01-1.06). All participants completed the study.

SIGNIFICANCE

Coadministration of lacosamide 400 mg/day did not alter the pharmacokinetics of warfarin 25 mg or the anticoagulation level. These results suggest that there is no need for dose adjustment of warfarin when coadministered with lacosamide.

Ideal characteristics of an antiepileptic drug: how do these impact treatment decisions for individual patients?

Effective management of epilepsy requires a holistic approach that takes into account the needs of the individual patient. Antiepileptic drug (AED) treatment must therefore look beyond efficacy to ensure that the patient's overall health status and quality of life (QoL) are optimized. Because the primary objective of AED treatment is to control seizures over the long term, the ideal AED should, first and foremost, demonstrate sustained efficacy and favourable tolerability. In addition, it should have a broad spectrum of activity; its pharmacokinetic profile should be stable and predictable and allow the option of once-daily dosing; and it should not interact with other medications and concomitant AEDs. Because the efficacy of first-line AEDs is broadly comparable, choice of treatment should be based on the individual patient's specific clinical characteristics. In particular, the primary and secondary prevention of comorbid conditions should be taken into consideration, because this can reduce the risk of mortality and improve health outcomes and QoL. Treatment selection must also take into account the patient's particular lifestyle and priorities, to maximize the likelihood of long-term treatment adherence. Advances in genetic testing may help inform choice of treatment - not only by elucidating a patient's underlying aetiology, but also by helping to avoid unnecessary side effects. Although certain patient populations (e.g. women of childbearing potential, adolescents, the elderly) require particular consideration when choosing the most appropriate treatment, every patient's unique clinical characteristics and personal circumstances must be taken into account to ensure treatment success and optimize their QoL.

Evaluation of unlicensed and off-label antiepileptic drugs prescribed to children: Brazilian Regulatory Agency versus FDA

BACKGROUND

Epileptic seizures are neurological disorders common in children; 4 to 10% of under 16-year olds have suffered at least one seizure. Antiepileptic drugs represent the basis of treatment for the majority of patients, but many of the drugs prescribed to pediatrics are used unlicensed and off-label.

OBJECTIVE

To analyze the prevalence of use of unlicensed and off-label antiepileptic drugs, by the pediatric population, according to the Food and Drug Administration and the Brazilian National Health Surveillance Agency. Setting General Hospital of the Faculty of Medicine at Ribeirão Preto, Brazil.

METHODS

A cross-sectional, retrospective and observational study was carried out. The daily prescriptions of children up to 12 years of age were collected for the analysis of antiepileptic drug use. Data of the registration number, sex, age, reason hospitalized, unit where hospitalized, drug prescribed, dosage, route and administration frequency were collected.

MAIN OUTCOME MEASURE

Antiepileptic drugs prescribed for children were classified as unlicensed and off-label according to the term of the product's license registered in the Food and Drug Administration and the Brazilian National Health Surveillance Agency.

RESULTS

Of the 6,637 pediatric patients identified during the study period, 583 (9.0%) received at least one antiepileptic drug. The most used antiepileptic drugs were phenobarbital, phenytoin, carbamazepine, valproic acid and clonazepam. As expected, the number of pharmaceutical dosage form classified as unlicensed or off-label was high in both agencies, but distinct between the two. The number of patients (n = 287) using unlicensed drugs was similar in the two agencies, but the use of off-label drugs was higher according to the analysis carried out by the North American agency (40.5%).

CONCLUSIONS

Old-generation antiepileptic drugs are widely prescribed to children. The results found for the use of off-label drugs demonstrate the absence of uniformity in action between the agencies and a lack of integration between the studies carried out. Although legislation on the licensing of drugs aims to protect the patients from drugs that have not been scientifically evaluated, the scarcity of data about the safety of the therapeutic resources obliges the doctors to prescribe unlicensed and off-label antiepileptic drugs to the pediatric population.

Methods for the quantitative evaluation and prediction of CYP enzyme induction using human in vitro systems

IMPORTANCE OF THE FIELD

For successful drug development, it is important to investigate the potency of candidate drugs causing drug-drug interactions (DDI) during the early stages of development. The most common mechanisms of DDIs are the inhibition and induction of CYP enzymes. Therefore, it is important to develop co.mpounds with lower potencies for CYP enzyme induction.

AREAS COVERED IN THIS REVIEW

The aim of the present paper is to present an overview of the current knowledge of CYP induction mechanisms, particularly focusing on the transcriptional gene activation mediated by pregnane X receptor, aryl hydrocarbon receptor and constitutive androstane receptor. The adoptable options of in vitro assay methods for evaluating CYP induction are also summarized. Finally, we introduce a method for the quantitative prediction of CYP3A4 induction considering the turnover of CYP3A4 mRNA and protein in hepatocytes based on the data obtained from a reporter gene assay.

WHAT THE READER WILL GAIN

In order to predict in vivo CYP enzyme induction quantitatively based on in vitro information, an understanding of the physiological induction mechanisms and the features of each in vitro assay system is essential. We also present the estimation method of in vivo CYP induction potency of each compound based on the in vitro data which are routinely obtained but not necessarily utilized maximally in pharmaceutical companies.

TAKE HOME MESSAGE

It is desirable to select compounds with lower potencies for the inductive effect. For this purpose, an accurate prioritization procedure to evaluate the induction potency of each compound in a quantitative manner considering the pharmacologically effective concentration of each compound is necessary.

Drug interactions in palliative care--it's more than cytochrome P450

OBJECTIVE

This study aims to identify the combination of substances with high potential for drug interactions in a palliative care setting and to provide concise recommendations for physicians.

METHODS

We used a retrospective systematic chart analysis of 200 consecutive inpatients. The recently developed and internationally advocated classification system OpeRational ClAssification of Drug Interactions was applied using the national database of the Federal Union of German Associations of Pharmacists. Charts of patients with potential for severe DDIs were examined manually for clinical relevance.

RESULTS

In 151 patients (75%) a total of 631 potential drug interactions were identified. Opioids (exception: methadone), non-opioids (exception: non-steroidal anti-inflammatory drugs), benzodiazepines, proton-pump inhibitors, laxatives, co-analgesics (exception: carbamazepine) and butylscopolamine were generally safe. High potential for drug interactions included combinations of scopolamine, neuroleptics, metoclopramide, antihistamines, non-steroidal anti-inflammatory drugs, (levo-) methadone, amitriptyline, carbamazepine and diuretics. The manual analyses of records from eight patients with risk for severe drug interactions provided no indicator for clinical relevance in these specific patients. Drug interactions attributed to the cytochrome pathway played a minor role (exception: carbamazepine).

CONCLUSION

Most relevant drug interactions can be expected with: (i) drugs (inter-) acting via histamine, acetylcholine or dopamine receptors; and (ii) Non-steroidal anti-inflammatory drugs. Even in last hours of life the combination of substances (e.g. anticholinergics) may produce relevant drug interactions (e.g. delirium).

PERSPECTIVE

Data on the potential for drug-drug interactions in palliative case is extremely scarce, but drug interactions can be limited if a few facts are considered. A synopsis of the findings of these studies is presented as concise recommendation to minimize drug interactions.

Adverse effects of antiepileptic drugs

More than 150 years after bromide was introduced as the first antiepileptic drug, adverse effects remain a leading cause of treatment failure and a major determinant of impaired health-related quality of life in people with epilepsy. Adverse effects can develop acutely or many years after starting treatment and can affect any organ or structure. In the past two decades, many efforts have been made to reduce the burden of antiepileptic drug toxicity. Several methods to screen and quantify adverse effects have been developed. Patient profiles associated with increased risk of specific adverse effects have been uncovered through advances in the areas of epidemiology and pharmacogenomics. Several new-generation antiepileptic drugs with improved tolerability profiles and reduced potential for drug interaction have been added to the therapeutic armamentarium. Overall, these advances have expanded the opportunities to tailor treatment with antiepileptic drugs, to enhance effectiveness and minimise the risk of toxic effects.

Antiepileptic drug monotherapy versus polytherapy: pursuing seizure freedom and tolerability in adults

PURPOSE OF REVIEW

Despite the availability of many new antiepileptic drugs (AEDs), only around 50% of people with epilepsy will become seizure free on their first drug. This article explores treatment options and issues influencing whether AEDs should be substituted or combined in the remainder of the patient population.

RECENT FINDINGS

Prior to the introduction of novel AEDs, it was generally opined that combining traditional agents did not necessarily lead to an improvement in seizure control and might increase the propensity for side effects. Newer AEDs, many with different mechanisms of action, have increased the potential for polytherapy regimens, although robust data to support or refute this therapeutic strategy are sparse. It seems sensible to substitute rather than combine when the first AED produces an idiosyncratic reaction, is poorly tolerated at a low/moderate dose or shows no efficacy. Polytherapy may be preferred if the patient tolerates their first or second AED well, but with a suboptimal response, particularly when there is an identifiable anatomical substrate for the seizures. AED selection requires consideration of many factors some of which are discussed in this study.

SUMMARY

There are no definitive answers on whether to combine or substitute AEDs. Different strategies are required for different scenarios in different patients.

Host factors affecting antiepileptic drug delivery-pharmacokinetic variability

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

Impact of age, weight and concomitant treatment on lamotrigine pharmacokinetics

WHAT IS KNOWN AND OBJECTIVE

Lamotrigine metabolism may be substantially altered with concomitant administration of valproic acid and/or carbamazepine. Such alterations may require the adjustment of lamotrigine dose to ensure optimal treatment efficacy and safety.

METHODS

The extent of lamotrigine interactions was investigated dependent on age, gender, weight and dose of concomitant carbamazepine and/or valproic acid in 65 patients with epilepsy. Lamotrigine plasma steady-state oral clearance (CLss/F) and area under the curve (AUCss) were calculated from the dose of drug, average steady-state concentration (Css) and interval of administration. Multiple regression analysis was used for the identification and quantification of factors that influenced lamotrigine pharmacokinetics.

RESULTS AND DISCUSSION

Age and dose of carbamazepine and valproic acid had significant influence on lamotrigine CLss/F and AUCss. Carbamazepine was associated with a dose-dependent increase and valproic acid with a dose-dependent decrease of lamotrigine metabolism rate. The effect of carbamazepine was more pronounced. Younger patients were expected to metabolize lamotrigine more rapidly whereas overweight patients may be less susceptible to interactions. Gender had no influence on lamotrigine pharmacokinetics.

WHAT IS NEW AND CONCLUSION

The efficacy and safety of lamotrigine may be altered by concomitant administration of carbamazepine and valproic acid. The models developed may be useful for estimating doses of lamotrigine for individual patients to minimize clinically significant interactions. Therapeutic monitoring is advisable when those drugs are used concomitantly.

An overview of the evidence and mechanisms of herb-drug interactions

Despite the lack of sufficient information on the safety of herbal products, their use as alternative and/or complementary medicine is globally popular. There is also an increasing interest in medicinal herbs as precursor for pharmacological actives. Of serious concern is the concurrent consumption of herbal products and conventional drugs. Herb-drug interaction (HDI) is the single most important clinical consequence of this practice. Using a structured assessment procedure, the evidence of HDI presents with varying degree of clinical significance. While the potential for HDI for a number of herbal products is inferred from non-human studies, certain HDIs are well established through human studies and documented case reports. Various mechanisms of pharmacokinetic HDI have been identified and include the alteration in the gastrointestinal functions with consequent effects on drug absorption; induction and inhibition of metabolic enzymes and transport proteins; and alteration of renal excretion of drugs and their metabolites. Due to the intrinsic pharmacologic properties of phytochemicals, pharmacodynamic HDIs are also known to occur. The effects could be synergistic, additive, and/or antagonistic. Poor reporting on the part of patients and the inability to promptly identify HDI by health providers are identified as major factors limiting the extensive compilation of clinically relevant HDIs. A general overview and the significance of pharmacokinetic and pharmacodynamic HDI are provided, detailing basic mechanism, and nature of evidence available. An increased level of awareness of HDI is necessary among health professionals and drug discovery scientists. With the increasing number of plant-sourced pharmacological actives, the potential for HDI should always be assessed in the non-clinical safety assessment phase of drug development process. More clinically relevant research is also required in this area as current information on HDI is insufficient for clinical applications.

Clinical decision support of therapeutic drug monitoring of phenytoin: measured versus adjusted phenytoin plasma concentrations

BACKGROUND

Therapeutic drug monitoring of phenytoin by measurement of plasma concentrations is often employed to optimize clinical efficacy while avoiding adverse effects. This is most commonly accomplished by measurement of total phenytoin plasma concentrations. However, total phenytoin levels can be misleading in patients with factors such as low plasma albumin that alter the free (unbound) concentrations of phenytoin. Direct measurement of free phenytoin concentrations in plasma is more costly and time-consuming than determination of total phenytoin concentrations. An alternative to direct measurement of free phenytoin concentrations is use of the Sheiner-Tozer equation to calculate an adjusted phenytoin that corrects for the plasma albumin concentration. Innovative medical informatics tools to identify patients who would benefit from adjusted phenytoin calculations or from laboratory measurement of free phenytoin are needed to improve safety and efficacy of phenytoin pharmacotherapy. The electronic medical record for an academic medical center was searched for the time period from August 1, 1996 to November 30, 2010 for patients who had total phenytoin and free phenytoin determined on the same blood draw, and also a plasma albumin measurement within 7 days of the phenytoin measurements. The measured free phenytoin plasma concentration was used as the gold standard.

RESULTS

In this study, the standard Sheiner-Tozer formula for calculating an estimated (adjusted) phenytoin level more frequently underestimates than overestimates the measured free phenytoin relative to the respective therapeutic ranges. Adjusted phenytoin concentrations provided superior classification of patients than total phenytoin measurements, particularly at low albumin concentrations. Albumin plasma concentrations up to 7 days prior to total phenytoin measurements can be used for adjusted phenytoin concentrations.

CONCLUSIONS

The results suggest that a measured free phenytoin should be obtained where possible to guide phenytoin dosing. If this is not feasible, then an adjusted phenytoin can supplement a total phenytoin concentration, particularly for patients with low plasma albumin.

Intravenous and oral levetiracetam in patients with a suspected primary brain tumor and symptomatic seizures undergoing neurosurgery: the HELLO trial

BACKGROUND

Levetiracetam (LEV) is a newer anticonvulsant with a favorable safety profile. There seem to be no relevant drug interactions, and an intravenous formulation is available. Therefore, LEV might be a suitable drug for the perioperative anticonvulsive therapy of patients with suspected brain tumors undergoing neurosurgery.

METHODS

In this prospective study (NCT00571155) patients with suspected primary brain tumors and tumor-related seizures were perioperatively treated with oral and intravenous LEV up to 4 weeks before and until 4 weeks after a planned neurosurgical procedure.

FINDINGS

Thirty patients with brain tumor-related seizures and intended neurosurgery were included. Three patients did not undergo the scheduled surgery after enrollment, and two patients were lost to follow-up. Therefore, 25 patients were fully evaluable. After initiation of therapy with LEV, 100% of the patients were seizure-free in the pre-surgery phase (3 days up to 4 weeks before surgery), 88% in the 48 h post-surgery phase and 84% in the early follow-up phase (48 h to 4 weeks post surgery). Treatment failure even after dose escalation to 3,000 mg/day occurred in three patients. No serious adverse events related to the treatment with LEV occurred.

CONCLUSION

Our data show the feasibility and safety of oral and intravenous LEV in the perioperative treatment of tumor-related seizures. Although this was a single arm study, the efficacy of LEV appears promising. Considering the side effects and interactions of other anticonvulsants, LEV seems to be a favorable option in the perioperative treatment of brain tumor-related seizures.

Pharmacokinetics of combined treatment with praziquantel and albendazole in neurocysticercosis

AIMS

Neurocysticercosis is the most common cause of acquired epilepsy in the world. Antiparasitic treatment of viable brain cysts is of clinical benefit, but current antiparasitic regimes provide incomplete parasiticidal efficacy. Combined use of two antiparasitic drugs may improve clearance of brain parasites. Albendazole (ABZ) has been used together with praziquantel (PZQ) before for geohelminths, echinococcosis and cysticercosis, but their combined use is not yet formally recommended and only scarce, discrepant data exist on their pharmacokinetics when given together. We assessed the pharmacokinetics of their combined use for the treatment of neurocysticercosis.

METHODS

A randomized, double-blind, placebo-controlled phase II evaluation of the pharmacokinetics of ABZ and PZQ in 32 patients with neurocysticercosis was carried out. Patients received their usual concomitant medications including an antiepileptic drug, dexamethasone, and ranitidine. Randomization was stratified by antiepileptic drug (phenytoin or carbamazepine). Subjects had sequential blood samples taken after the first dose of antiparasitic drugs and again after 9 days of treatment, and were followed for 3 months after dosing.

RESULTS

Twenty-one men and 11 women, aged 16 to 55 (mean age 28) years were included. Albendazole sulfoxide concentrations were increased in the combination group compared with the ABZ alone group, both in patients taking phenytoin and patients taking carbamazepine. PZQ concentrations were also increased by the end of therapy. There were no significant side effects in this study group.

CONCLUSIONS

Combined ABZ + PZQ is associated with increased albendazole sulfoxide plasma concentrations. These increased concentrations could independently contribute to increased cysticidal efficacy by themselves or in addition to a possible synergistic effect.

Blood-brain barrier P450 enzymes and multidrug transporters in drug resistance: a synergistic role in neurological diseases

Drug penetration into the central nervous system (CNS) is controlled by the blood-brain barrier (BBB). Even though a number of strategies to circumvent the BBB and to improve drug access have been developed, drug resistance in CNS diseases remains an unmet clinical problem. We here review the mechanisms by which a healthy or pathological BBB influences drug distribution in the brain, with emphasis on the role of P450 metabolic enzymes and multi-drug transporter (MDT) proteins. In addition to the classic hepatic and gut biotransformation pathways, CNS expression of P450 enzymes may bear pharmacokinetic and pharmacodynamic significance exerting a metabolic activity and transforming parent drugs into specific products. We propose these mechanisms to play a major role in CNS drug resistant pathologies including refractory forms of epilepsy. Changes in the cerebrovascular hemodynamic conditions can affect expression of P450 enzymes and MDT proteins. This should be taken into account when developing in vitro experimental approaches to reproduce the physiological or pathological properties of the BBB. Finally, a link between P450 and MDT expression in the diseased brain and cell survival is discussed.