Clinical pharmacokinetics of newer antiepileptic drugs. Lamotrigine, vigabatrin, gabapentin and oxcarbazepine

Pharmacokinetics and tissue distribution of vigabatrin enantiomers in rats

Purpose

To investigate the pharmacokinetics and tissue distribution of VGB racemate and its single enantiomers, and explore the potential of clinic development for single enantiomer S-VGB.

Methods

In the pharmacokinetics study, male Sprague-Dawley rats were gavaged with VGB racemate or its single enantiomers dosing 50, 100 or 200 mg/kg, and the blood samples were collected during 12 h at regular intervals. In the experiment of tissue distribution, VGB and its single enantiomers were administered intravenously dosing 200 mg/kg, and the tissues including heart, liver, spleen, lung and kidney, eyes, hippocampus, and prefrontal cortex were separated at different times. The concentrations of R-VGB and S-VGB in the plasma and tissues were measured using HPLC.

Results

Both S-VGB and R-VGB could be detected in the plasma of rats administered with VGB racemate, reaching Cmax at approximately 0.5 h with t1/2 2-3 h. There was no significant pharmacokinetic difference between the two enantiomers when VGB racemate was given 200 mg/kg and 100 mg/kg. However, when given at the dose of 50 mg/kg, S-VGB presented a shorter t1/2 and a higher Cl/F than R-VGB, indicating a faster metabolism of S-VGB. Furthermore, when single enantiomer was administered respectively, S-VGB presented a slower metabolism than R-VGB, as indicated by a longer t1/2 and MRT but a lower Cmax. Moreover, compared with the VGB racemate, the single enantiomers S-VGB and R-VGB had shorter t1/2 and MRT, higher Cmax and AUC/D, and lower Vz/F and Cl/F, indicating the stronger oral absorption and faster metabolism of single enantiomer. In addition, regardless of VGB racemate administration or single enantiomer administration, S-VGB and R-VGB had similar characteristics in tissue distribution, and the content of S-VGB in hippocampus, prefrontal cortex and liver was much higher than that of R-VGB.

Conclusions

Although there is no transformation between S-VGB and R-VGB in vivo, those two enantiomers display certain disparities in the pharmacokinetics and tissue distribution, and interact with each other. These findings might be a possible interpretation for the pharmacological and toxic effects of VGB and a potential direction for the development and optimization of the single enantiomer S-VGB.

Gabapentin affects the expression of inflammatory mediators on healthy gingival cells

Gabapentin is one of the most used drugs to treat postoperative pain with antihyperalgesic properties and has a unique mechanism of action, which differentiates it from other commonly used drugs. Various studies have shown that the perioperative use of gabapentin reduces postoperative pain. In our study, fragments of gingival tissue of healthy volunteers were collected during operation. Gene expression of 29 genes was investigated in gingival fibroblasts cell culture treated with gabapentin, compared with untreated cells. Of the different chemokines and interleukins studied, only 10 were statistically significant (CCL1, CCR1, CCR4, CCR5, CCR6, ILI1A, ILI1B, IL5, IL6R, TNFSF10). The overexpression of these cytokines, obtained in many studies, leads us to think that gabapentin can interact and cause post-inflammatory gingival hyperplasia, but, probably, in our study the gabapentin has not the same effect, because we used gingival fibroblasts of healthy people.

Long-term vigabatrin treatment modifies pentylenetetrazole-induced seizures in mice: focused on GABA brain concentration

BACKGROUND

The goal of our study was to examine the long-term effect of vigabatrin (VGB), a γ-aminobutyric acid aminotransferase (GABA-AT) inhibitor on clonazepam (CLO), ethosuximide (ETX) and valproate (VPA) anticonvulsive activity against pentylenetetrazole (PTZ)-induced seizures in mice.

METHODS

VGB was administered for 3 and 7 days. Convulsions were evoked by PTZ at its CD97 (99 mg/kg). The influence of CLO, ETX and VPA alone or in combination with VGB on motor performance and long-term memory was analyzed. γ-aminobutyric acid (GABA) concentration in mice brain and plasma as well as glutamate decarboxylase (GAD) activity was measured.

RESULTS

After 3 days of treatment, VGB in doses up to 500 mg/kg increased PTZ-induced seizure threshold, whereas after 7 days VGB (at the dose of 125 mg/kg) inhibited clonic seizures in experimental mice. 7 days of VGB administration did not change the protective effect of CLO, ETX and VPA against PTZ-induced seizures. 7 days of VGB treatment at a subthreshold dose of 75 mg/kg decreased TD50 of ETX and CLO in the chimney test, but did not affect TD50 value for VPA. 7 days of VGB administration in combination with AEDs did not affect long-term memory in mice. VGB after 3 days or 7 days of administration increased brain GABA concentration. GAD activity was decreased after 3 and 7 days of VGB administration.

CONCLUSIONS

The presented results confirm anticonvulsive activity of VGB through GABA metabolism alteration and suggest care when combining VGB with ETX or CLO in the therapy.

Update on the use of new anticonvulsants as mood stabilisers

Aims and method

The aim of the study was to assess and update the data related to the use of lamotrigine, gabapentia topiramate and tiagabine as mood stabilisers. The published trials and case reports were collated from searches of the Cochrane Collaboration, Medline and Micromedex from January 1985 to January 1999. The manufacturers were also contacted.

The search included other aspects of the usage of these anticonvulsants, such as side-effects and drug interactions.

Results

Most of the data are in the form of anecdotal case reports and small scale open studies. The majority of the trials lack a placebo arm and do not use standard rating scales or standard diagnostic criteria. The usefulness of the results is partly limited by the short durations and small sample sizes. Furthermore, it is often unclear whether concomitant medication was altered.

Therefore, any conclusion of effectiveness requires confirmation in double-blind placebo-controlled studies to eliminate any false-positive response due to bias, placebo effects or random variability. There is also possibility of false-negative selection bias, as the early data tends to relate to a more refractory population. The use of these newer anticonvulsants as mood stabilisers is currently under investigation in a clinical trial programme.

Clinical implications

There are no studies comparing the new anticonvulsants either with each other or with established agents. There is less evidence supporting the use of the newer anticonvulsants in bipolar disorders compared with established agents. The newer anticonvulsants should be used as third- or fourth-line agents. There is more data supporting the use of lamotrigine and gabapentin.

Pharmacokinetics and Saturable Absorption of Gabapentin in Nursing Home Elderly Patients

Pharmacokinetic data of gabapentin (GBP) in community-dwelling elderly patients show a significant effect of advanced age on GBP pharmacokinetics due to altered renal function. However, there are no data in elderly nursing home (NH) patients to evaluate gabapentin absorption and elimination. Our objective was to characterize the pharmacokinetics of GBP in elderly nursing home patients maintained on GBP therapy. This was a prospective pharmacokinetic study in elderly nursing home patients (≥60 years) receiving GBP for the management of chronic pain or epilepsy from seven nursing homes. Pharmacokinetic parameters were estimated by nonlinear mixed-effects modeling. A one-compartment model described the data and clearance (CL) was associated with estimated glomerular filtration rate (eGFR) (p < 0.0001). The GBP CL in elderly nursing home patients was 2.93 L/h. After adjusting for the effect of GFR, GBP CL was not affected by age, sex, body weight, or comorbidity scores. No significant effects of body size measures, age, and sex were detected on volume of distribution. Dose-dependent bioavailability of GBP was demonstrated, and the saturable absorption profile was described by a nonlinear hyperbolic function. Prediction-corrected visual predictive check (pc-VPC) suggests adequate fixed- and random-effects models that successfully simulated the mean trend and variability in gabapentin concentration-time profiles. In this analysis, the parameters of the hyperbolic nonlinearity appear to be similar between elderly and younger adults.

Options for perioperative pain management in neurosurgery

Moderate-to-severe pain following neurosurgery is common but often does not get attention and is therefore underdiagnosed and undertreated. Compounding this problem is the traditional belief that neurosurgical pain is inconsequential and even dangerous to treat. Concerns about problematic effects associated with opioid analgesics such as nausea, vomiting, oversedation, and increased intracranial pressure secondary to elevated carbon dioxide tension from respiratory depression have often led to suboptimal postoperative analgesic strategies in caring for neurosurgical patients. Neurosurgical patients may have difficulty or be incapable of communicating their need for analgesics due to neurologic deficits, which poses an additional challenge. Postoperative pain control should be a priority, because pain adversely affects recovery and patient outcomes. Inconsistent practices and the quality of current analgesic strategies for neurosurgical patients still leave room for improvement. Given the complexity of postoperative pain management for these patients, multimodal strategies are often required to optimize pain control and at the same time limit undesired side effects.

Pharmacokinetic effects of simultaneous administration of single-dose gabapentin 500 mg and zolpidem tartrate 10 mg in healthy volunteers: a randomized, open-label, crossover trial

Objective

Gabapentin is being investigated as a potential treatment for occasional disturbed sleep. This study assessed the pharmacokinetics and tolerability of gabapentin 500 mg and the commonly prescribed sedative/hypnotic zolpidem tartrate 10 mg, administered separately and in combination.

Methods

Forty healthy participants (19 male, 21 female) were randomized into this three-period crossover study [mean (range) age 34.1 (18–45) years, weight 68.3 (51.4–92.7) kg; 60 % white]. Participants were dosed with gabapentin alone (n = 39), zolpidem tartrate alone (n = 38), and the combination (gabapentin + zolpidem) (n = 38) over three treatment periods, which were separated by ≥7 days. Blood samples were collected pre-dose and 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 18, 24 and 36 h post-dose. Plasma concentrations of each drug were assayed using validated methods. Pharmacokinetic parameters were estimated from plasma concentration–time data using standard non-compartmental methods.

Results

For gabapentin + zolpidem combination versus gabapentin alone, mean pharmacokinetic parameters were peak plasma concentration (C_max) 4.61 versus 4.72 µg/mL, time to C_max (t_max) 4.63 versus 3.64 h and the area under plasma concentration–time curve extrapolated to infinity (AUC_0–∞) 53.4 versus 51.0 µg h/mL. For the combination versus zolpidem alone, mean pharmacokinetic parameters were C_max 154 versus 138 ng/mL, t_max 1.45 versus 1.84 h and AUC_0–∞ 912 versus 854 ng h/mL. The 90 % confidence intervals for C_max (rate of absorption) and AUC_0–∞ (extent of absorption) comparing the combination versus single drug administration fell within the 80–125 % range accepted for bioequivalence. All treatments were well tolerated.

Conclusion

The pharmacokinetics of gabapentin 500 mg and zolpidem tartrate 10 mg are unaffected when both drugs are taken simultaneously, compared with each drug taken alone.

Pharmacokinetic aspects of the anti-epileptic drug substance vigabatrin: focus on transporter interactions

Drug transporters in various tissues, such as intestine, kidney, liver and brain, are recognized as important mediators of absorption, distribution, metabolism and excretion of drug substances. This review gives a current status on the transporter(s) mediating the absorption, distribution, metabolism and excretion properties of the anti-epileptic drug substance vigabatrin. For orally administered drugs, like vigabatrin, the absorption from the intestine is a prerequisite for the bioavailability. Therefore, transporter(s) involved in the intestinal absorption of vigabatrin in vitro and in vivo are discussed in detail. Special focus is on the contribution of the proton-coupled amino acid transporter 1 (PAT1) for intestinal vigabatrin absorption. Furthermore, the review gives an overview of the pharmacokinetic parameters of vigabatrin across different species and drug–food and drug–drug interactions involving vigabatrin.

Gabapentin in acute postoperative pain management

Gabapentin (1-aminomethyl-cyclohexaneacetic acid) is an amino acid that has the structure of the neurotransmitter γ-aminobutyric acid (GABA). It is a novel drug used for the treatment of postoperative pain with antihyperalgesic properties and a unique mechanism of action. Gabapentin and the related, more potent compound pregabalin have been shown to be beneficial in the treatment of neuropathic pain as well as postoperative pain following spinal surgery and hysterectomy. This study reviews five aspects of gabapentin: (1) chemical and structural characteristics; (2) pharmacokinetics and pharmacodynamics; (3) application in acute pain management; (4) adverse effects; and (5) drug safety. Overall, gabapentin has been reported to be a safe and efficacious drug for the treatment of postoperative pain.

Administration of four different doses of gabapentin reduces awakening from breakthrough pain and adverse effects in outpatients with neuropathic pain during the initial titration

Background

Gabapentin is a safe and well-tolerated anticonvulsant with a wide therapeutic index, and it is used for neuropathic pain. The aim of this study was to compare previous dosing methods with the administration of four different doses of gabapentin while maintaining the same maximum daily dose for the safe administration of high doses of the medication.

Methods

The subjects were outpatients with various neuropathic pain syndromes, with at least two of the following symptoms: allodynia, burning pain, shooting pain, or hyperalgesia. The TID group received equal doses of gabapentin 3 times per day, while the QID group received 4 different doses of gabapentin per day. The pain score, frequency of breakthrough pain (BTP), severity and the duration of pain, sleep disturbance due to nocturnal pain, and adverse effects were recorded each day.

Results

The average daily pain score and sleep disturbance were significantly reduced in the QID group between days 3 and 10 of the experiment. The adverse effects of the medication were also reduced in the QID group. However, the frequency of BTP and severity and duration of pain were not significantly different between two groups.

Conclusions

Administration of 4 different doses of gabapentin during the initial titration in outpatients with neuropathic pain resulted in a significant reduction in awakening from breakthrough pain and a reduction in the adverse effects of the medication.

Once-daily gastroretentive gabapentin for the management of postherpetic neuralgia: an update for clinicians

Gabapentin was originally developed as an add-on anticonvulsant drug, but has been widely used in the USA for the management of postherpetic neuralgia since its approval for this indication in 2002. Gabapentin has a short elimination half life and limited absorption due to a saturable L-amino acid transport system, which is expressed predominantly in the proximal small intestine. Hence, the original immediate-release gabapentin formulation (gabapentin TID) must usually be taken three times a day for optimal efficacy. Gabapentin TID is also associated with a high incidence of dizziness and somnolence and some patients are unable to tolerate the doses required for maximum pain relief. A once-daily, gastroretentive formulation of gabapentin was recently approved by the US Food and Drug Administration (FDA) for the management of postherpetic neuralgia. This formulation provides gradual release of gabapentin to the optimal site of absorption in the proximal small intestine and reduces the chance of saturating intestinal uptake, thus enabling once-daily dosing of gabapentin. This gradual release and absorption have been demonstrated in pharmacokinetic studies in healthy subjects. The efficacy of once-daily gastroretentive gabapentin for the management of postherpetic neuralgia has been demonstrated in placebo-controlled clinical studies. In addition, data from these studies suggest that the incidence of dizziness and somnolence may be reduced compared with similar studies using gabapentin TID. This article provides an overview of the pharmacokinetics, efficacy, and safety of once-daily gastroretentive gabapentin for the management of postherpetic neuralgia.

Once-daily gastroretentive gabapentin for treatment of postherpetic neuralgia

SUMMARY The immediate-release formulation of gabapentin (gabapentin three-times daily) is approved for treatment of postherpetic neuralgia (PHN). Although it has a low propensity for drug–drug interactions, it requires multiple daily dosing and is associated with a high frequency of dizziness and somnolence. A once-daily formulation of gabapentin was recently approved for the treatment of PHN. This formulation employs a gastroretentive technology to provide a prolonged release of gabapentin. Clinical studies have confirmed the efficacy of once-daily, gastroretentive gabapentin in the treatment of PHN. In addition, these studies have suggested that the rate of dizziness and somnolence may be reduced compared with similar studies using gabapentin three-times daily. This article reviews key aspects of the pharmacology, efficacy and safety of once-daily gabapentin in the treatment of PHN.

Population pharmacokinetics of pregabalin in healthy subjects and patients with chronic pain or partial seizures

PURPOSE

Pregabalin, a high-affinity ligand for α2δ subunits of voltage-gated calcium channels, is a novel pharmacotherapy for chronic pain, partial seizures, and other disorders. The present study investigated the population pharmacokinetics of pregabalin following single and multiple doses in healthy volunteers and patient populations.

METHODS

Using nonlinear mixed-effect modeling, 5,583 plasma pregabalin concentration-time samples from 1,723 subjects were analyzed: 2,868 samples from healthy volunteers or subjects with renal impairment (n = 123), 1,513 from patients with partial seizures (n = 626), and 1,202 from patients with chronic pain (n = 974). A one-compartment model with first-order elimination and absorption processes and absorption lag time was used.

KEY FINDINGS

This pharmacostatistical model showed that: (1) pregabalin oral clearance (CL/F) was directly proportional to creatinine clearance (CLcr), but was independent of gender, race, age, female hormonal status, daily dose, and dosing regimen; (2) apparent volume of distribution was dependent on body weight and gender; (3) absorption rate was decreased when given with food; and (4) coadministration with marketed antiepileptic drugs (AEDs) had no significant effect on pregabalin CL/F.

SIGNIFICANCE

Pregabalin CL/F is related to CLcr, and this relationship is similar among healthy volunteers and patients with either partial seizures or chronic pain disorders. The only factor having a clinically significant influence on steady-state plasma pregabalin concentrations is renal function.

[Specific aspects of treatment for women with bipolar affliction]

This manuscript summarizes specific issues in the disease course and pharmacological treatment of women with bipolar disorders. Gender differences relevant to the female biology manifest in symptoms, outcome, and course. The preponderance of depressive symptoms is typical, and the risk of rapid cycling is estimated to be eight times higher for women than for men. Comorbid anxiety and eating disorders occur more frequently in female patients. In planning treatment it is important to take fertility, contraception, and pregnancy into consideration and adjust the pharmacotherapy to harmonize with the patient's current phase of life. Little is known about potential sexual dysfunctions of bipolar women. Further research should include clinical and observational studies focusing on gender-specific differences in symptomatology, treatment, and long-term outcome of bipolar disorders.

A non-randomized study to investigate the effects of the atypical antipsychotic aripiprazole on the steady-state pharmacokinetics of lamotrigine in patients with bipolar I disorder

OBJECTIVE

To determine the effect of aripiprazole on steady-state pharmacokinetics of lamotrigine in patients with bipolar I disorder who were clinically stable on lamotrigine (100-400 mg/day) for >or=4 weeks.

METHODS

In this open-label study, aripiprazole was administered at 10 mg/day for 3 days, 20 mg/day for 3 days, then 30 mg/day for 8 days. Blood samples were collected on Days -1 and 14 for determination of lamotrigine steady-state pharmacokinetic parameters. Safety and tolerability were assessed.

RESULTS

Eighteen patients were administered aripiprazole in combination with lamotrigine. Geometric mean (GM) values for lamotrigine maximum plasma concentration were similar for lamotrigine alone (26 ng/mL) and with co-administered aripiprazole (23 ng/mL). GM values for plasma lamotrigine area under the concentration-time curve (AUCtau) were comparable for lamotrigine alone (434 ng/h/mL) and with co-administered aripiprazole (394 ng/h/mL). Median T(max) of lamotrigine alone and combined with aripiprazole was 1.98 and 0.77 h, respectively. No changes to lamotrigine dose-normalized plasma trough concentrations were observed with co-administered aripiprazole. Sixteen patients (88.9%) experienced >or=1 adverse event (AE), the most common of which was insomnia (n = 6).

CONCLUSIONS

Aripiprazole had no meaningful effect on lamotrigine steady-state pharmacokinetics in patients with bipolar I disorder. No dosage adjustment of lamotrigine is required and the combination was generally safe and well tolerated.

Treatment of refractory complex partial seizures: role of vigabatrin

Vigabatrin (VGB) is an antiepileptic drug that was designed to inhibit GABA-transaminase, and increase levels of gamma-amino-butyric acid (GABA), a major inhibitory neurotransmitter in the brain. VGB has demonstrated efficacy as an adjunctive antiepileptic drug for refractory complex partial seizures (CPS) and for infantile spasms (IS). This review focuses on its use for complex partial seizures. Although VGB is well tolerated, there have been significant safety concerns about intramyelinic edema and visual field defects. VGB is associated with a risk of developing bilateral concentric visual field defects. Therefore, the use of VGB for complex partial seizures should be limited to those patients with seizures refractory to other treatments. Patients must have baseline and follow-up monitoring of visual fields, early assessment of its efficacy, and ongoing evaluation of the benefits and risks of VGB therapy.

Isobolographic and behavioral characterizations of interactions between vigabatrin and gabapentin in two experimental models of epilepsy

The aim of this study was to characterize the pharmacodynamic, pharmacokinetic and adverse-effect profiles of vigabatrin and gabapentin. Isobolographic analysis was used in two mouse experimental models of epilepsy: the maximal electroshock seizure threshold test and pentylenetetrazole-induced seizures. In the maximal electroshock seizure threshold test, electroconvulsions were produced by a current with various intensities whilst in the pentylenetetrazole test a CD(97) dose (100 mg/kg) was used. Potential adverse-effect profiles of interactions of vigabatrin with gabapentin at three fixed-ratios of 1:3, 1:1 and 3:1 from both seizure tests were evaluated in the chimney (motor performance) and grip-strength (skeletal muscular strength) tests. Vigabatrin and gabapentin total brain concentrations were determined with high performance liquid chromatography. Vigabatrin and gabapentin administered singly increased the electroconvulsive threshold (TID(20) - 226.2 and 70.0 mg/kg, respectively). With isobolography, the combination of vigabatrin with gabapentin at the fixed-ratio of 1:3 exerted supra-additive (synergistic) interactions whilst at 1:1 and 3:1 additivity occurred. Similarly, vigabatrin and gabapentin administered singly suppressed the pentylenetetrazole-induced seizures (ED(50) values - 622.5 and 201.1 mg/kg, respectively). Isobolography revealed that vigabatrin with gabapentin in combination at the fixed-ratio of 1:1 produced supra-additive (synergistic) interaction whilst at 1:3 and 3:1 additivity occurred. In combination neither motor coordination nor skeletal muscular strength was affected. Total vigabatrin and gabapentin brain concentrations revealed that neither drug affected the pharmacokinetics of the other. Vigabatrin and gabapentin have a favorable pharmacodynamic interaction in animal seizure models in the absence of acute adverse effects or concurrent pharmacokinetic changes.

Antiepileptic drug development in children: considerations for a revisited strategy

The European Commission and the European Parliament have acknowledged the specific need for a proper evaluation of new drugs in children. The evaluation of the antiepileptic drugs (AEDs) available on the market illustrates the deficit in therapeutic trials for childhood epilepsy syndromes. Currently, the development of AEDs is mainly performed in children with focal epilepsy, whereas infants and the specific age-related epilepsy syndromes, particularly epileptic encephalopathies, are neglected. Infantile epilepsies remain 'therapeutic orphans', although they are the most frequent and deleterious disorders in the area of epilepsy. In order to circumvent the difficulties faced when conducting AED trials in children, we addressed the question of improving feasibility without decreasing quality, while optimally taking into account paediatric ethical requirements. For this review, we first raise the issues of paediatric epilepsies that require special considerations for randomized controlled trials (RCTs) in children. Then, we attempt to determine to what extent adult data could be extrapolated to children. Finally, we review innovative approaches that could be used in the evaluation of AEDs in children. The main specificities of paediatric epilepsies (heterogeneity, severity, cognitive impact, pharmacoresistance, syndrome-specific efficacy profile) are related to brain development and should be taken into consideration when establishing specific guidelines for the evaluation of AEDs in children. Extrapolating efficacy data from adults to children may be possible in focal epilepsy except in infants who need age-specific trials. Epileptic encephalopathies do not exist in adults and require specific trials. Pharmacokinetic data are required below a lower age limit for extrapolation of adult data to be determined in a case-to-case approach. Safety data are required at any paediatric age. RCTs in small but homogeneous populations in each paediatric-specific epileptic syndrome, the use of sequential or responder-enrichment designs, and population pharmacokinetics represent potentially promising approaches to evaluate drugs in children in an efficient way.

Isobolographic characterization of interactions between vigabatrin and tiagabine in two experimental models of epilepsy

To characterize the type of interactions between vigabatrin (VGB) and tiagabine (TGB) -- two newer antiepileptic drugs influencing GABA-ergic neurotransmitter system, the isobolographic analysis was used in two experimental models of epilepsy: the maximal electroshock seizure threshold (MEST) test and pentylenetetrazole (PTZ)-induced seizures in mice. Results indicated that VGB and TGB administered separately (i.p.) increased the electroconvulsive threshold in mice, which allowed the calculation of their TID(20) values (threshold increasing doses by 20% over the threshold of control animals) in the MEST test. The TID(20) for VGB was 226.2 mg/kg and that for TGB was 4.4 mg/kg. With isobolography, the combinations of VGB with TGB (at fixed-ratios of 1:3, 1:1 and 3:1) exerted additive interactions in the MEST test in mice. Similarly, VGB and TGB injected separately (i.p.) suppressed the PTZ-induced seizures, and their ED(50) values (median effective doses, protecting 50% of the animals tested against clonic convulsions) for VGB and TGB were 622.5 mg/kg and 0.8 mg/kg, respectively. Isobolographic analysis of interactions revealed that the combinations of VGB with TGB at the fixed-ratios of 1:3 and 1:1 produced supra-additive (synergistic) interactions against PTZ-induced seizures. Only the combination of VGB with TGB at the fixed-ratio of 3:1 was additive in the PTZ test. The evaluation of acute adverse-effect potential for all fixed-ratio combinations of VGB with TGB (administered at their TID(20) and ED(50) values from the MEST and PTZ tests) revealed that none of the examined combinations affected motor coordination in the chimney test and altered neuromuscular tone in the grip-strength test in mice. In contrast, VGB in combinations with TGB produced the antinociceptive effects with respect to suppression of acute thermal pain in animals subjected to the hot-plate test. Based on this preclinical study, one can ascertain that the combination of VGB with TGB would provide an adequate seizure control in epileptic patients.

Pharmacokinetics, toxicology and safety of lamotrigine in epilepsy

Optimisation of pharmacotherapy for epilepsy requires consideration of the impact of drug metabolism and toxicology on the therapeutic profiles and clinical use of antiepileptic drugs (AEDs). This review discusses the pharmacokinetics and toxicology of the AED lamotrigine, and considers the implications of these data for optimising its use in the management of epilepsy. Lamotrigine has good absorption, minimal plasma protein binding and linear pharmacokinetics. Partly because of these properties, frequent dosing adjustments are generally unnecessary, and therapeutic monitoring is not required under most circumstances. Lamotrigine is not associated with clinically significant neurological, cognitive, metabolic, hepatic or reproductive endocrine toxicity. Like other AEDs, including carbamazepine and phenytoin, lamotrigine has been associated with serious rash. With some exceptions, lamotrigine has relatively few clinically relevant drug interactions, a characteristic important in reducing safety risks, especially among patients who require polytherapy. The clinical impact of pharmacokinetic interactions between lamotrigine and enzyme-inducing AEDs or valproate can be minimised by adhering to recommended dose-escalation schedules with demonstrated reliability in clinical trials and clinical practice. Likewise, adhering to recommended dosing guidelines can minimise the risk of lamotrigine-associated rash. The pharmacokinetic, toxicology and safety profiles of lamotrigine make the drug suitable for use across a spectrum of patients with epilepsy.

Use of Antiepileptic Drugs in Patients with Kidney Disease

The number of medications used to treat different types of seizures has increased over the last 10-15 years. Most of the newer antiepileptic drugs (AEDs) are likely to be unfamiliar to many nephrologists. For both the older and newer AEDs, basic pharmacokinetic information, recommendations for drug dosing in patients with reduced kidney function or who are on dialysis, and adverse renal and fluid-electrolyte effects are reviewed. Newer AEDs are less likely to have significant drug-drug interactions than older agents, but are more likely to need dosage adjustment in patients with reduced kidney function. The most common renal toxicities of these drugs include metabolic acidosis, hyponatremia, and nephrolithiasis; interstitial nephritis and other adverse effects are less common. Little is known about the clearance of most of the newer AEDs with high-efficiency hemodialyzers or with peritoneal dialysis. Monitoring of drug levels when available, careful clinical assessment of patients taking AEDs, and close collaboration with neurologists is essential to the management of patients taking AEDs.

Determination of gabapentin in human plasma and urine by high-performance liquid chromatography with UV-vis detection

A simple and reliable high-performance liquid chromatographic (HPLC) method with UV-vis detection has been developed and validated for the determination of gabapentin (GBP) in human plasma and urine. The clean up of the sample was carried out by solid-phase extraction with C18-cartridge. After the clean up procedure, the samples were pre-column derivatizated with 1,2-naphthoquinone-4-sulphonic acid sodium salt (NQS). A chromatographic separation was achieved on a C18 column with a mobile phase consisting of acetonitrile and 10mM orthophosphoric acid (pH 2.5) with isocratic elution (35:65). Baclofen was used as an internal standard (I.S.). The method developed for GBP was linear over the concentration range of 0.05-5.0 microg/ml and 0.1-10.0 microg/ml for plasma and urine, respectively. The method is precise (relative standard deviation, R.S.D. <4.05%) and accurate (relative mean error, RME <0.15%); mean absolute recoveries were 72.21% for plasma and 72.73% for urine.

Oxcarbazepine in the treatment of bipolar disorder: a review

OBJECTIVE

To review the data on the efficacy of oxcarbazepine (OXC) in bipolar disorder (BD) and to provide recommendations for clinicians on the use of this medication in treating BD.

METHOD

Using the terms oxcarbazepine and bipolar disorder, oxcarbazepine and mania, or oxcarbazepine and bipolar depression, we conducted a computer-aided search of MEDLINE for the years 1950 to 2005.

RESULTS

Case reports, retrospective chart reviews, open prospective studies, and double-blind studies reported the efficacy and effectiveness of OXC in treating BD. The data indicate that OXC has efficacy in treating acute mania and may be a useful add-on in treating acute bipolar depression and in BD prophylaxis. OXC is generally well-tolerated.

CONCLUSION

We recommend using OXC as monotherapy or as add-on therapy in refractory mania, but we recommend it be used predominantly as an add-on treatment for other phases of BD in patients who have not improved with well-established treatments or in patients who have difficulty tolerating adequate dosages.

Bilateral SUNCT syndrome associated to chronic maxillary sinus disease

SUNCT syndrome (short lasting unilateral neuralgiform headache with conjuntival injection and tearing) is defined as short attacks of periorbital unilateral pain and accompanied by ipsilateral lacrimation and redness of the same eye. We present an unusual SUNCT case with bilateral pain that started five years ago after an acute maxillary sinus infection that evolved to chronic sinusitis. This association has been described in few SUNCT cases, but its causal role remains uncertain. The patient was a 58 years old man that fulfilled a headache diary that showed the usual circadian pattern, worsening in the morning and afternoon, and responded to treatment with gabapentina. He was submitted to a functional endoscopic sinus surgery and evolved with milder pain. In a review of 21 patients, 5 had a past medical history of sinusitis, but the causal role of this association remained uncertain.

Gabapentin is Effective in the Treatment of Cancer-Related Neuropathic Pain: A Prospective, Open-Label Studya,b

BACKGROUND

Gabapentin has been evaluated in the treatment of nonmalignant neuropathic pain, however, there is little direct evidence evaluating its efficacy in cancer-related neuropathic pain.

OBJECTIVE

This study evaluated the effectiveness of gabapentin to treat cancer-related neuropathic pain.

DESIGN

This was an open-label study. Two parallel groups of patients were recruited with either treatment-related (radiotherapy, surgery, chemotherapy) or tumor-related neuropathic pain. Gabapentin was dose-escalated from 300 mg/d to 1.8 g/d.

MEASUREMENTS

The primary outcome, pain, was assessed using the modified brief pain inventory. In addition patient descriptors of pain and scores of activities of daily living were collated together with demographic data.

RESULTS

We recruited 62 patients with treatment-related (n = 25) or tumor-related (n = 37) neuropathic pain. There was a significant reduction in the worst, average, and current pain scores (p < 0.002), but not the least pain score (p = 0.21). Twenty-eight of 62 (45.2%) of patients achieved at least a one third reduction in pain score (95% confidence interval [CI] 32.5-58.3); the number needed to treat to obtain this benefit is 2.2 (95% CI 1.7-3.1). There was a significant reduction in all scores measuring the impact of pain on daily living (p < 0.003). There was no significant difference in pain scores at day 8 compared to day 15. Analysis of variance suggested that gender, but not etiology, or type of neuropathic pain, was a significant predictor of analgesic response and this warrants further investigation.

CONCLUSION

We conclude that gabapentin is an effective treatment for cancer-related neuropathic pain.

Pregabalin: a new neuromodulator with broad therapeutic indications

OBJECTIVE

To review pregabalin's pharmacology, pharmacokinetics, efficacy, and adverse effects in the treatment of neuropathic pain, epilepsy, and anxiety.

DATA SOURCES

A MEDLINE search (1993-October 2005) for peer-reviewed English-language publications was performed. Abstracts from professional meetings were also included. Key terms were anxiety, diabetic neuropathy, epilepsy, neuropathic pain, postherpetic neuralgia, pregabalin, and seizures.

STUDY SELECTION AND DATA EXTRACTION

Basic pharmacology data were extracted from animal studies; pharmacokinetic data were extracted from human studies. Multicenter, double-blind, placebo-controlled, parallel-group studies were included to describe the efficacy and adverse effects of pregabalin.

DATA SYNTHESIS

Pregabalin is a new agent that exerts its pharmacodynamic effect by modulating voltage-gated calcium channels. Pregabalin has a linear pharmacokinetic profile. It is completely absorbed, not bound to plasma proteins, not metabolized, and eliminated unchanged through the kidneys. Doses must be adjusted in patients with renal insufficiency. Clinical trials showed that pregabalin is effective in neuropathic pain associated with postherpetic neuralgia, diabetic peripheral neuropathy, in partial epilepsy as adjunctive therapy, and in generalized and social anxiety disorders. The most common adverse effects were dizziness and somnolence. Few serious adverse effects were reported. Pregabalin should not be discontinued rapidly.

CONCLUSIONS

Pregabalin is an effective and safe analgesic, antiepileptic, and anxiolytic medicine. It will provide a new treatment option for patients with neuropathic pain and partial epilepsy.

Use of lamotrigine to augment clozapine in patients with resistant schizophrenia and comorbid alcohol dependence: a potent anti-craving effect?

Comorbid alcohol dependence is common in patients with schizophrenia and is associated with a variety of serious adverse consequences. Although case reports exist concerning the positive impact of lamotrigine addition on clozapine treatment in resistant schizophrenia, a review of the literature fails to document any evidence regarding a combination of the two in the treatment of patients with schizophrenia and comorbid alcohol dependence. In the present study, we present three cases in which patients with resistant schizophrenia and comorbid alcohol use disorder were given lamotrigine to augment clozapine. Our findings suggest that clozapine plus lamotrigine may be helpful in reducing alcohol consumption and craving among patients with schizophrenia and comorbid alcohol dependence.

Psychopharmacologic treatment of aggression in children and adolescents

Knowledge regarding psychopharmacology is increasingly based on clinical trials and rational algorithms. Medications are increasingly regarded as useful adjuncts in the treatment of maladaptive aggression, whether it appears as a target symptom or as a complication of a whole range of psychopathology. Properly integrated into a treatment package that uses psychotherapies and environmental manipulation, medications can provide relief from one of the most destructive forms of psychopathology. Still, more controlled clinical trials are needed, especially those comparing active interventions and those testing the synergistic and antagonistic effects of different treatment modalities.

Lamotrigine: a review of its use in bipolar disorder

Lamotrigine (Lamictal), a phenyltriazine derivative, is a well established anticonvulsant agent that has shown efficacy in the prevention of mood episodes in adult patients with bipolar I disorder. The mechanism of action of the drug in patients with bipolar disorder may be related to the inhibition of sodium and calcium channels in presynaptic neurons and subsequent stabilisation of the neuronal membrane. Lamotrigine monotherapy significantly delayed time to intervention with additional pharmacotherapy or electroconvulsive therapy for any new mood episode (mania, hypomania, depression and mixed episodes), compared with placebo, in two large, randomised, double-blind trials of 18 months' duration. Additionally, lamotrigine was significantly superior to placebo at prolonging time to intervention for depression. These effects of lamotrigine were demonstrated in both recently manic/hypomanic and recently depressed patients. Lamotrigine showed efficacy in delaying manic/hypomanic episodes in pooled data only, although lithium was superior to lamotrigine on this measure. Two of four double-blind, short-term studies have shown lamotrigine to be more effective than placebo in the treatment of patients with treatment-refractory bipolar disorder or those with bipolar depression. Lamotrigine has not demonstrated efficacy in the treatment of acute mania. Lamotrigine was generally well tolerated in maintenance studies with the most common adverse events being headache, nausea, infection and insomnia. Incidences of diarrhoea and tremor were significantly lower in lamotrigine- than in lithium-treated patients. The incidence of serious rash with lamotrigine treatment was 0.1% in all studies of bipolar disorder and included one case of mild Stevens-Johnson syndrome. Lamotrigine did not appear to cause bodyweight gain. The dosage of lamotrigine is titrated over a 6-week period to 200 mg/day to minimise the incidence of serious rash. Adjustments to the initial and target dosages are required if coadministered with valproate semisodium or carbamazepine.

CONCLUSION

Lamotrigine has been shown to be an effective maintenance therapy for patients with bipolar I disorder, significantly delaying time to intervention for any mood episode. Additionally, lamotrigine significantly delayed time to intervention for a depressive episode and showed limited efficacy in delaying time to intervention for a manic/hypomanic episode, compared with placebo. Although not approved for the short-term treatment of mood episodes, lamotrigine has shown efficacy in the acute treatment of patients with bipolar depression but has not demonstrated efficacy in the treatment of acute mania. Lamotrigine is generally well tolerated, does not appear to cause bodyweight gain and, unlike lithium, generally does not require monitoring of serum levels.

Acute effects of gabapentin on laboratory measures of aggressive and escape responses of adult parolees with and without a history of conduct disorder

RATIONALE

The possible role of GABA in human aggression was evaluated by administering gabapentin to subjects with and without a history of conduct disorder and comparing the effects on laboratory measures of aggression and escape.

METHODS

Eighteen male and two female subjects with a history of criminal behavior participated in experimental sessions, which measured aggressive and escape responses. Ten subjects had a history of childhood conduct disorder (CD+) and ten subjects with no history (non-CD controls). Aggression was measured using the Point Subtraction Aggression Paradigm (PSAP), which provided subjects aggressive, escape and monetary reinforced response options.

RESULTS

Acute doses (200, 400 and 800 mg) of gabapentin had similar effects on aggressive responses among CD+ subjects compared to non-CD control subjects. Aggressive responses of CD+ and non-CD control subjects increased at lower gabapentin doses, and decreased at the highest 800 mg gabapentin dose. Gabapentin increased escape responses for both CD+ and non-CD controls CD- subjects at the lowest dose, but then produced dose-related decreases at the two higher doses in both groups. No changes in monetary reinforced responses were observed, indicative of no CNS stimulation or sedation.

CONCLUSIONS

Gabapentin produced similar bitonic effects upon aggressive and escape responses in subjects with and without a history of childhood conduct disorder. This is in marked contrast to prior differential effects of baclofen on aggressive responses between CD+ and non-CD control subjects in a previous study.

Gabapentin in the treatment of neuropathic pain

This paper reviews the pharmacology and clinical effectiveness of gabapentin in the treatment of neuropathic pain. Gabapentin has antihyperalgesic and antiallodynic properties but does not have significant actions as an anti-nociceptive agent. Its mechanisms of action appear to be a complex synergy between increased GABA synthesis, non-NMDA receptor antagonism and binding to the alpha2delta subunit of voltage dependent calcium channels. The latter action inhibits the release of excitatory neurotransmitters. Clinically, several large randomized controlled trials have demonstrated its effectiveness in the treatment of a variety of neuropathic pain syndromes. Patients with neuropathic pain can expect a mean reduction in pain score of 2.05 points on an 11 point numerical rating scale compared with a reduction of 0.94 points if they had taken the placebo. Around 30% of patients can expect to achieve more than 50% pain relief and a similar number will also experience minor adverse events; the most common of which are somnolence and dizziness. In patients with neuropathic pain due to cancer, higher response rates might be observed with gabapentin when administered with opioids because of a synergistic interaction.

Pharmacokinetics and metabolism of 14C-levetiracetam, a new antiepileptic agent, in healthy volunteers

The absorption, disposition and metabolism of levetiracetam, a new antiepileptic drug, have been investigated after a single oral dose of the (14)C-labelled molecule administered to male healthy volunteers. As chiral inversion can occur during drug metabolism, the chiral inversion of levetiracetam and/or of its major metabolite produced by hydrolysis (the corresponding acid) was also investigated. Finally, the in vitro hydrolysis of levetiracetam to its major metabolite and the inhibition of this reaction in human blood have been studied. Levetiracetam was very rapidly absorbed in man, with the peak plasma concentration of the unchanged drug occurring at 0.25-0.50 h. The unchanged drug accounted for a very high percentage of plasma radioactivity (97-82%) at all the times measured, i.e. until 48 h after administration. The apparent volume of distribution of the compound was close (0.55-0.62 l/kg) to the volume of total body water. Total body clearance (0.80-0.97 ml/min/kg) was much lower than the nominal hepatic blood flow. The plasma elimination half-life of the unchanged drug varied between 7.4 h and 7.9 h. Plasma to blood ratio of total radioactivity concentrations was 1.1-1.3, showing that radioactivity concentrations were similar in blood cells and plasma. The balance of excretion was very high in all four volunteers. The predominant route of excretion was via urine, accounting for a mean of 95% of the administered dose after 4 days. Two major radioactive components were present in urine, the unchanged drug and the acid obtained by hydrolysis, accounting for 66% and 24% of the dose after 48 h, respectively. Hydrolysis of levetiracetam in human blood followed Michaelis-Menten kinetics with Km and V(max) values of 435 microM and 129 pmol/min/ml blood, respectively. Among the inhibitory agents investigated in this study, only paraoxon inhibited levetiracetam hydrolysis (92% inhibition at 100 microM). Oxidative metabolism occurred in man, although it accounted for no more than 2.5% of the dose. There was no evidence of chiral inversion.

Gender differences in bipolar disorder

The presentation and course of bipolar disorder differs between women and men. The onset of bipolar disorder tends to occur later in women than men, and women more often have a seasonal pattern of the mood disturbance. Women experience depressive episodes, mixed mania, and rapid cycling more often than men. Bipolar II disorder, which is predominated by depressive episodes, also appears to be more common in women than men. Comorbidity of medical and psychiatric disorders is more common in women than men and adversely affects recovery from bipolar disorder more often in women. Comorbidity, particularly thyroid disease, migraine, obesity, and anxiety disorders occur more frequently in women than men, whereas substance use disorders are more common in men. Although the course and clinical features of bipolar disorder differ between women and men, there is no evidence that gender affects treatment response to mood stabilizers. However, women may be more susceptible to delayed diagnosis and treatment. Treatment of women during pregnancy and lactation is challenging because available mood stabilizers pose potential risks to the developing fetus and infant. Pregnancy neither protects nor exacerbates bipolar disorder, and many women require continuation of medication during the pregnancy. The postpartum period is a time of high risk for onset and recurrence of bipolar disorder in women, and prophylaxis with mood stabilizers might be needed. Individualized risk/benefit assessments of pregnant and postpartum women with bipolar disorder are required to promote the health of the woman and avoid or limit exposure of the fetus or infant to potential adverse effects of medication.

Pharmacokinetic interaction between retigabine and lamotrigine in healthy subjects

PURPOSE

The antiepileptic drugs (AEDs) retigabine (RGB) and lamotrigine (LTG) undergo predominantly N-glucuronidation and renal excretion. This study was performed to evaluate potential pharmacokinetic interactions between both AEDs.

METHODS

Twenty-nine healthy male subjects participated in the study. Group A ( n=14) received single oral 200-mg RGB doses on day 1 and day 7, and 25 mg o.i.d. LTG on days 3-8. Group B ( n=15) received single oral 200-mg LTG doses on day 1 and day 17, and was up-titrated to 300 mg RGB b.i.d. on days 6-20. Blood samples were collected to compare the pharmacokinetics of both AEDs and the N-acetyl metabolite of RGB (AWD21-360) after single and concomitant treatments.

RESULTS

RGB was rapidly absorbed and eliminated with a mean half-life (t(1/2)) of 6.3+/-1.1 h and an apparent clearance (CL/F) of 0.69+/-1.4 l/h/kg. Under co-administration of LTG, mean RGB t(1/2) and area under the plasma concentration-time curve (AUC) were increased by 7.5% ( P=0.045) and 15% ( P=0.006), respectively, while CL/F was decreased by 13% ( P=0.06). Consistent results were obtained for AWD21-360. LTG was moderately rapidly absorbed, eliminated with a mean t(1/2) of 37+/-10.4 h and a CL/F of 0.028+/-0.007 l/h/kg. Under co-administration of RGB, mean LTG t(1/2) and AUC decreased by 15% and 18%, respectively, while CL/F increased by 22% (all parameters, P=0.001).

CONCLUSIONS

RGB and LTG exhibit a modest pharmacokinetic interaction on each other. The slight decline in RGB clearance due to LTG is believed to result from competition for renal elimination rather than competition for glucuronidation. The induction of LTG clearance due to retigabine was unexpected since RGB did not show enzyme induction in various other drug-drug interaction studies. Further studies in patients are needed to assess the clinical relevance of these findings for concomitant treatment with both drugs in the upper recommended dose range.

Acute antimanic efficacy and safety of oxcarbazepine in an open trial with an on-off-on design

RATIONALE AND OBJECTIVES

Carbamazepine has shown reasonable antimanic properties, but its use has been limited because of enzyme-inducing effects. The keto-derivative oxcarbazepine (OXC) is very similar to carbamazepine, however, the metabolic pathway is different. OXC is not metabolized to the 10, 11-epoxide, which seems to be responsible for several undesirable side-effects of carbamazepine and furthermore OXC has less enzyme-inducing properties.

METHODS

In this non-random open label study, patients were treated with OXC for 14 days, crossed over to no OXC for 7 days, and then crossed back over to OXC for the remaining 14 days. OXC was titrated to a final dose in a range of 900-2100 mg due to individual response. Treatment success was defined as a reduction of the original Young Mania Rating Scale (YMRS) score of more than 50% at the end of study period.

RESULTS

Four of the 12 included patients (33%) met defined response criteria at the end of study period. Fifty percentage of the patients had to be prematurely excluded from the trial. The mean YMRS scores of the on-periods were obviously different from the off-period. Forty-two percentage of the patients experienced side-effects leading to premature discontinuation in two of 12 patients.

CONCLUSION

Antimanic activity of OXC was demonstrated in this pilot study only for patients with mild or moderate manic symptoms. Further studies are encouraged to clarify OXC's role as mood-stabilizer and assess whether it has a profile similar to that of carbamazepine.

Population pharmacokinetics of gabapentin in infants and children

PURPOSE

To characterize gabapentin pharmacokinetics in infants and children using a population approach and to identify important demographic and/or physiologic determinants of gabapentin disposition.

METHODS

Gabapentin was administered in single doses of 10 mg/kg (N=48 healthy subjects, age 1 month-12 years) or in multiple doses of 10-65 mg/kg per day (N=205 patients with epilepsy, age 2 months-13 years) at 08:00, 14:00, and 20:00. Serial concentration-time data from the healthy subjects were combined with sparse data obtained in patients and were modeled using NONMEM.

RESULTS

Gabapentin oral clearance (l/h) was directly related to creatinine clearance (ml/min) with a slope of 0.116. The slope of the relationship was 36% greater in blacks than in subjects of other races. When oral clearance was normalized for body weight, young children (<5 years) had higher and more variable values than older children. Volume of distribution was related to body weight and appeared to differ between subjects and patients. Intersubject variability was approximately 30% for oral clearance and volume of distribution and was larger for the absorption rate constant and lag time. Residual variability, a measure of intrasubject variability and measurement error, was smaller in subjects than in patients.

CONCLUSIONS

On a weight basis, 33% larger doses would be required in younger children (<5 years) to achieve the same exposure as older children.

Gabapentin treatment for bipolar disorders

OBJECTIVE

[corrected] To review the effectiveness data on the use of gabapentin in bipolar disorders.

DATA SOURCES

Clinical literature was accessed through MEDLINE (January 1985-November 2000). Key search terms included gabapentin, mood stabilizer, and bipolar disorder.

DATA SYNTHESIS

Bipolar disorder is a complex condition that can be difficult to treat effectively. Mood stabilizers are increasingly being used to manage bipolar disorder. Studies that used gabapentin in bipolar disorders are evaluated.

CONCLUSIONS

From the data presented, gabapentin cannot be recommended for treatment of bipolar disorder. Further studies are required to determine whether gabapentin has any role in the management of bipolar disorder.

Evaluation of human intestinal absorption data and subsequent derivation of a quantitative structure–activity relationship (QSAR) with the Abraham descriptors

The human intestinal absorption of 241 drugs was evaluated. Three main methods were used to determine the human intestinal absorption: bioavailability, percentage of urinary excretion of drug-related material following oral administration, and the ratio of cumulative urinary excretion of drug-related material following oral and intravenous administration. The general solvation equation developed by Abraham's group was used to model the human intestinal absorption data of 169 drugs we considered to have reliable data. The model contains five Abraham descriptors calculated by the ABSOLV program. The results show that Abraham descriptors can successfully predict human intestinal absorption if the human absorption data is carefully classified based on solubility and administration dose to humans.

Oxcarbazepine, an antiepileptic agent

BACKGROUND

Epilepsy is a common neurologic condition. Many of the currently approved pharmacologic agents for its treatment are associated with numerous adverse drug reactions and drug interactions.

OBJECTIVE

This review describes the pharmacology and therapeutic use of oxcarbazepine, an analogue of the well-known antiepileptic agent carbamazepine.

METHODS

Articles for review were identified through a search of MEDLINE, International Pharmaceutical Abstracts, and EMBASE for the years 1980 through 2000. The terms used individually and in combination were oxcarbazepine, carbamazepine, epilepsy, and seizures.

RESULTS

Oxcarbazepine and its primary metabolite have been effective in animal models of epilepsy that generally predict efficacy in generalized tonic-clonic seizures and partial seizures in humans. The exact mechanism of action of oxcarbazepine is unknown, although as with carbamazepine, it is believed to involve blockade of voltage-gated sodium channels. The pharmacokinetic profile of oxcarbazepine is less complicated than that of carbamazepine, with less metabolism by the cytochrome P450 system, no production of an epoxide metabolite, and lower plasma protein binding. The clinical efficacy and tolerability of oxcarbazepine have been demonstrated in trials in adults, children, and the elderly. In a double-blind, randomized, crossover trial in adults, oxcarbazepine 300 mg was associated with a decrease in the mean frequency of tonic seizures (21.4 vs 30.5 seizures during steady-state periods) and tonic-clonic seizures (8.2 vs 10.4) compared with carbamazepine 200 mg (P = 0.05). A multinational, multicenter, double-blind, placebo-controlled, randomized, 28-week trial assessed the efficacy and tolerability of oxcarbazepine at doses of 600, 1200, and 2400 mg as adjunctive therapy in patients with uncontrolled partial seizures. All 3 oxcarbazepine groups demonstrated a reduction in seizure frequency per 28-day period compared with placebo (600 mg, 26% reduction; 1200 mg, 40% reduction; 2400 mg, 50% reduction; placebo, 7.6% reduction; all, P < 0.001). A trial in children assessed the efficacy and toxicity of oxcarbazepine (median dose, 31.4 mg/kg/d) as adjunctive therapy for partial seizures. Patients receiving oxcarbazepine experienced a 35% reduction in seizure frequency, compared with a 9% reduction in the placebo group (P < 0.001). The most common adverse effects associated with oxcarbazepine are related to the central nervous system (eg, dizziness, headache, diplopia, and ataxia) and the gastrointestinal system (eg, nausea and vomiting). Compared with carbamazepine, there is an increased risk of hyponatremia with oxcarbazepine. The frequency and severity of drug interactions are less with oxcarbazepine than with carbamazepine or other antiepileptic agents.

CONCLUSIONS

Oxcarbazepine may be considered an appropriate alternative to carbamazepine for the treatment of partial seizures in patients who are unable to tolerate carbamazepine. Its use in nonseizure disorders remains to be examined in large-scale clinical trials, and pharmacoeconomic comparisons of oxcarbazepine with other antiepileptic agents, particularly carbamazepine, are needed.

Effect of vigabatrin and gabapentin on phenytoin pharmacokinetics in the dog

This study was aimed at investigating whether or not the kinetics of intravenously administered phenytoin (PT) was altered by oral administration of vigabatrin (VGB) or gabapentin (GBP). A daily dose of PT (12 mgkg(-1)i.v.) was given to a group of five beagle dogs for a period of 1 week. On day eight, plasma samples were serially collected over 24 h, after administration of the PT dose. PT administration was continued, along with supplementary oral VGB (60 mgkg(-1)) for another week and then plasma samples were collected for analysis of PT levels. The same protocol was followed for the PT (12 mgkg(-1), i.v.)-GBP (300 mg caps., p.o.) study on a separate group (n= 5) of dogs. Orally administered GBP did not significantly alter the pharmacokinetic parameters of parenteral PT. However VGB markedly changed the drug's kinetics, as evidenced by a 31% (P= 0.015) reduction in total body clearance (CL) and an increase of over 45% in half-life (t(1/2)), (P= 0.013) and area under the plasma PT concentration-time curve (AUC), (P= 0.044). GBP does not appear to have any pharmacokinetic interaction with PT, while coadministration of VGB and PT results in a marked reduction in systemic clearance of the latter in the dog.