Antiepileptic drug interactions - principles and clinical implications

Effect of eslicarbazepine acetate on the pharmacokinetics of a combined ethinylestradiol/levonorgestrel oral contraceptive in healthy women

OBJECTIVE

To investigate the effect of once-daily (QD) eslicarbazepine acetate (ESL) 800 mg and 1,200 mg administration on pharmacokinetics of a combined ethinylestradiol/levonorgestrel oral contraceptive (OC) in women of childbearing potential.

METHODS

Two two-way, crossover, two-period, randomized, open-label studies were performed in 20 healthy female subjects, each. In one period (ESL+OC period), subjects received ESL 800 mg QD in one study and ESL 1200 mg QD in the other study, for 15 days; concomitantly with the Day 14 ESL dose, an oral single dose of 30 μg ethinylestradiol and 150 μg levonorgestrel was administered. In the other period (OC alone), a single dose of 30 μg ethinylestradiol and 150 μg levonorgestrel was administered. Three weeks or more separated the periods. An analysis of variance (ANOVA) was used to test for differences between pharmacokinetic parameters of 30 μg ethinylestradiol and 150 μg levonorgestrel following ESL+OC and OC alone, and 90% confidence intervals (90%CI) for the ESL+OC/OC alone geometric mean ratio (GMR) were calculated.

RESULTS

ESL significantly decreased the systemic exposure to both ethinylestradiol and levonorgestrel. GMR (90%CI) for AUC0-24 of ethinylestradiol were 68% (64%; 71%) following 1,200 mg ESL and 75% (71%; 79%) following 800 mg ESL. GMR (90%CI) for AUC0-24 of levonorgestrel were 76% (68%; 86%) following 1,200 mg ESL and 89% (82%; 97%) following 800 mg ESL.

CONCLUSIONS

A clinically relevant dose-dependent effect of ESL administration on the pharmacokinetics of ethinylestradiol and levonorgestrel was observed. Therefore, to avoid inadvertent pregnancy, women of childbearing potential should use other adequate methods of contraception during treatment with ESL, and, in case ESL treatment is discontinued, until CYP3A4 activity returns to normal.

Second-generation antiepileptic drugs and pregnancy: a guide for clinicians

When treating pregnant women with antiepileptic drugs (AEDs), clinicians have to balance potential fetal adverse effects against the risks of uncontrolled maternal disease. Only recently have emerging scientic data provided a rational basis for treatment decisions considering both aspects. The focus of research is currently moving from the first to the second AED generation. Lamotrigine is relatively well studied, and data on other novel AEDs, such as levetiracetam, oxcarbazepine, topiramate, zonisamide, gabapentin and pregabalin, are in progress. Safety issues appear to be favorable for lamotrigine, and preliminary results are also promising for levetiracetam and oxcarbazepine. Drugs metabolized by uridine-diphospate glucuronosyl transferase or excreted unchanged by the kidneys are particularly susceptible to increased body clearance during pregnancy. Lamotrigine is subject to both mechanisms, and therapeutic serum levels may sometimes be difficult to maintain. The authors review the recommendations and clinical research on modern AED treatment during pregnancy, highlighting current experience with second-generation drugs.

The World Federation of Societies of Biological Psychiatry (WFSBP) guidelines for the biological treatment of bipolar disorders: update 2012 on the long-term treatment of bipolar disorder

OBJECTIVES

These guidelines are based on a first edition that was published in 2004, and have been edited and updated with the available scientific evidence up to October 2012. Their purpose is to supply a systematic overview of all scientific evidence pertaining to the long-term treatment of bipolar disorder in adults.

METHODS

Material used for these guidelines are based on a systematic literature search using various data bases. Their scientific rigor was categorised into six levels of evidence (A-F) and different grades of recommendation to ensure practicability were assigned.

RESULTS

Maintenance trial designs are complex and changed fundamentally over time; thus, it is not possible to give an overall recommendation for long-term treatment. Different scenarios have to be examined separately: Prevention of mania, depression, or an episode of any polarity, both in acute responders and in patients treated de novo. Treatment might differ in Bipolar II patients or Rapid cyclers, as well as in special subpopulations. We identified several medications preventive against new manic episodes, whereas the current state of research into the prevention of new depressive episodes is less satisfactory. Lithium continues to be the substance with the broadest base of evidence across treatment scenarios.

CONCLUSIONS

Although major advances have been made since the first edition of this guideline in 2004, there are still areas of uncertainty, especially the prevention of depressive episodes and optimal long-term treatment of Bipolar II patients.

A quick review of carbamazepine pharmacokinetics in epilepsy from 1953 to 2012

BACKGROUND

Carbamazepine has been used as AEDs since 1965, and is most effective against partial seizures. Two basic mechanisms of action have been proposed: 1) enhancement of sodium channel inactivation by reducing high-frequency repetitive firing of action potentials, 2) and action on synaptic transmission. The aim of this study was to provide a review of carbamazepine pharmacokinetics and its management guidelines in Iranian epileptic population.

MATERIALS AND METHODS

Directory of Open Access Journals (DOAJ), Google Scholar, Pubmed (NLM), LISTA (EBSCO), Web of Science were searched; 1600, 722 and 167 research and review articles relevant to the topics; carbamazepine pharmacokinetics, carbamazepine pharmacokinetics in epilepsy and review on carbamazepine pharmacokinetics in epilepsy were found, respectively.

RESULTS

Carbamazepine is highly bound to plasma proteins. In patients the protein-bound fraction ranged from 75-80% of the total plasma concentration. Bioavailability ranges from 75-85%. The rate or extent of absorption was not be affected by food. It is completely metabolized and the main metabolite is carbamazepine-epoxide (CBZ-E). Carbamazepine induces its own metabolism, leading to increased clearance, shortened serum half-life, and progressive decrease in serum levels. Increases in daily dosage are necessary to maintain plasma concentration. Severe liver dysfunction may cause disordered pharmacokinetics. In cardiac failure, congestion of major vital organs, including kidneys, may result in abnormally slow absorption and metabolism.

CONCLUSION

Carbamazepine shows variability due to its narrow therapeutic window. Therefore clinical management in a3n Iranian epileptic population should focus on results derived from therapeutic drug monitoring in order to reduce inter and intra- individual variability in plasma drug concentrations.

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.

Toxic epidermal necrolysis due to lamotrigine in a pediatric patient

A 12-year-male child developed toxic epidermal necrolysis (TEN) probably due to lamotrigine. The patient was on antiepileptic therapy (sodium valproate and clonazepam) since 6–7 months, and lamotrigine was added in the regimen 1–2 months back. A serious cutaneous reaction is more likely to occur during the first 2 months of starting lamotrigine. The use of lamotrigine as an add-on to valproate may have precipitated the reaction. Other drugs were ruled out based on the incubation period of TEN. Drug interactions should be kept in mind with multiple antiepileptic therapies. The patient died because of the severity of reactions and delay in starting the treatment with steroids. One must be vigilant in early detection of the reaction.

The role of reactive species in epileptogenesis and influence of antiepileptic drug therapy on oxidative stress

Epilepsy is considered one of the most common neurological disorders. The focus of this review is the acquired form of epilepsy, with the development process consisting of three major phases, the acute injury phase, the latency epileptogenesis phase, and the phase of spontaneous recurrent seizures. Nowadays, an increasing attention is paid to the possible interrelationship between oxidative stress resulting in disturbance of physiological signalling roles of calcium and free radicals in neuronal cells and mitochondrial dysfunction, cell damage, and epilepsy. The positive stimulation of mitochondrial calcium signals by reactive oxygen species and increased reactive oxygen species generation resulting from increased mitochondrial calcium can lead to a positive feedback loop. We propose that calcium can pose both, physiological and pathological effects of mitochondrial function, which can lead in neuronal cell death and consequent epileptic seizures. Various antiepileptic drugs may impair the endogenous antioxidative ability to prevent oxidative stress. Therefore, some antiepileptic drugs, especially from the older generation, may trigger oxygen-dependent tissue injury. The prooxidative effects of these antiepileptic drugs might lead to enhancement of seizure activity, resulting in loss of their efficacy or apparent functional tolerance and undesired adverse effects. Additionally, various reactive metabolites of antiepileptic drugs are capable of covalent binding to macromolecules which may lead to deterioration of the epileptic seizures and systemic toxicity. Since neuronal loss seems to be one of the major neurobiological abnormalities in the epileptic brain, the ability of antioxidants to attenuate seizure generation and the accompanying changes in oxidative burden, further support an important role of antioxidants as having a putative antiepileptic potential.

Pharmacokinetic interaction between ivabradine and phenytoin in healthy subjects

BACKGROUND

Phenytoin is an inductor of the main metabolizing enzyme of ivabradine and it could influence its pharmacokinetics. Changes in ivabradine pharmacokinetics could have clinical significance regarding the safety of the treatment.

OBJECTIVE

The study objective was evaluation of the pharmacokinetic interaction between ivabradine and phenytoin in healthy subjects.

METHODS

A single dose of ivabradine 10 mg was administered alone or in combination with phenytoin 150 mg to 18 healthy subjects in a two-treatment study design, separated by 5 days in which the phenytoin alone was administered at a dose of 150 mg twice daily. Plasma concentrations of ivabradine were determined during a 12-hour period following drug administration, using a high-throughput liquid chromatography coupled with mass spectrometry analytical method. Pharmacokinetic parameters of ivabradine administered in each treatment were calculated using non-compartmental analysis and compared to determine if the differences were statistically significant.

RESULTS

In the two treatment periods, the mean ± SD peak plasma concentrations (C(max)) were 18.6 ± 8.0 ng/mL (ivabradine alone) and 6.5 ± 3.1 ng/mL (ivabradine after pre-treatment with phenytoin). The mean ± SD times taken to reach C(max) (t(max)) were 1.2 ± 0.7 h and 0.8 ± 0.6 h, respectively, and the total areas under the plasma concentration-time curve from time zero to infinity (AUC(∞)) were 62.3 ± 18.7 ng · h/mL and 19.2 ± 17.0 ng · h/mL, respectively. Statistically significant differences were observed for the C(max) and AUC(∞) of ivabradine when administered alone or with phenytoin, whereas for t(max) and the half-life the differences were non-significant.

CONCLUSION

This study showed that phenytoin has an important effect on the pharmacokinetics of ivabradine in healthy subjects, reducing its bioavailability by approximately 70%.

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.

The effect of combination therapy on the plasma concentrations of traditional antiepileptics: a retrospective study

The present study aimed at determining the differences in plasma concentrations of traditional antiepileptics such as phenytoin, carbamazepine, and valproic acid in patients receiving monotherapy and combination therapy. In addition, the effect of gender and age on plasma drug concentration was evaluated in these patients. For this purpose, plasma trough concentrations obtained during routine therapeutic monitoring of these drugs were assessed retrospectively. The average plasma concentrations reached the apparent therapeutic ranges, except for the average plasma concentration of phenytoin, which was below the therapeutic range in patients who received only phenytoin or in combination with the other agents. Phenytoin when combined with carbamazepine or valproic acid significantly decreased the average plasma concentrations of these drugs to subtherapeutic concentrations. The results showed that plasma carbamazepine concentrations were higher in men than in women, whereas plasma concentrations of valproic acid and phenytoin were higher in women than in men. The difference in this regard between men and women was found to be statistically significant for phenytoin. The difference between the average plasma concentrations of carbamazepine, phenytoin, and valproic acid among age groups was not significant. In conclusion, our study measured the average plasma antiepileptic drug concentrations in patients with epilepsy who were receiving monotherapy and combination therapy and were routinely monitored, and has thus shown the importance of drug monitoring in the evaluation of the effectiveness of these drugs.

Statin medication in patients treated with antiepileptic drugs in Norway

PURPOSE

The lipid-lowering response of statins metabolized by cytochrome P450 3A4 (CYP3A4) has previously been shown to be diminished by concurrent use of enzyme-inducing antiepileptic drugs (EIAEDs). The aim of this study was to compare statin prescription in patients receiving EIAEDs versus non-enzyme-inducing antiepileptic drugs (NEIAEDs), before and after introduction of prescribing restrictions for statins in Norway.

METHODS

The Norwegian Prescription Database was used to extract data on patients using antiepileptic drugs and statins during 2004 and 2008. Statin type and dose used were compared between patients treated with at least one EIAED (i.e., carbamazepine, phenobarbital, phenytoin, primidone) and those receiving NEIAEDs only (i.e., all other antiepileptic drugs).

RESULTS

The number of included patients co-medicated with statins and AEDs was 4855 in 2004 and 9880 in 2008. Among these patients, 2827 and 3160, respectively, were treated with EIAEDs. The CYP3A4 statins (i.e., simvastatin, atorvastatin and lovastatin) accounted for 85% of all statins in 2004, increasing to 93% in 2008. There was no significant difference in the likelihood of being prescribed a CYP3A4 statin versus a non-CYP3A4 statin among patients receiving EIAEDs and NEIAEDs. The average daily dose of individual CYP3A4 statins was not different between the AED groups.

CONCLUSIONS

The present study shows that the interaction risk between CYP3A4-metabolized statins and EIAEDs is largely overlooked in Norwegian clinical practice. To avoid therapeutic failure of statin treatment in patients using AEDs, implementation of strategies for systematic management of drug interactions is warranted.