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Mechanism Of Action
The pharmacological activity of Trileptal is primarily exerted through the 10-monohydroxy metabolite (MHD) of oxcarbazepine. The precise mechanism by which oxcarbazepine and MHD exert their antiseizure effect is unknown; however, in vitro electrophysiological studies indicate that they produce blockade of voltage-sensitive sodium channels, resulting in stabilization of hyperexcited neural membranes, inhibition of repetitive neuronal firing, and diminution of propagation of synaptic impulses. These actions are thought to be important in the prevention of seizure spread in the intact brain. In addition, increased potassium conductance and modulation of high-voltage activated calcium channels may contribute to the anticonvulsant effects of the drug. No significant interactions of oxcarbazepine or MHD with brain neurotransmitter or modulator receptor sites have been demonstrated.
Oxcarbazepine and its active metabolite (MHD) exhibit anticonvulsant properties in animal seizure models. They protected rodents against electrically induced tonic extension seizures and, to a lesser degree, chemically induced clonic seizures, and abolished or reduced the frequency of chronically recurring focal seizures in Rhesus monkeys with aluminum implants. No development of tolerance (i.e., attenuation of anticonvulsive activity) was observed in the maximal electroshock test when mice and rats were treated daily for five days and four weeks, respectively, with oxcarbazepine or MHD.
Following oral administration of Trileptal tablets, oxcarbazepine is completely absorbed and extensively metabolized to its pharmacologically active 10-monohydroxy metabolite (MHD). In a mass balance study in people, only 2% of total radioactivity in plasma was due to unchanged oxcarbazepine, with approximately 70% present as MHD, and the remainder attributable to minor metabolites.
The half-life of the parent is about two hours, while the half-life of MHD is about nine hours, so that MHD is responsible for most antiepileptic activity.
Based on MHD concentrations, Trileptal tablets and suspension were shown to have similar bioavailability.
After single-dose administration of Trileptal tablets to healthy male volunteers under fasted conditions, the median tmax was 4.5 (range 3 to 13) hours. After single-dose administration of Trileptal oral suspension to healthy male volunteers under fasted conditions, the median tmax was six hours.
Steady-state plasma concentrations of MHD are reached within 2-3 days in patients when Trileptal is given twice a day. At steady state the pharmacokinetics of MHD are linear and show dose proportionality over the dose range of 300 to 2400 mg/day.
Effect of Food: Food has no effect on the rate and extent of absorption of oxcarbazepine from Trileptal tablets. Although not directly studied, the oral bioavailability of the Trileptal suspension is unlikely to be affected under fed conditions. Therefore, Trileptal tablets and suspension can be taken with or without food.
The apparent volume of distribution of MHD is 49L.
Approximately 40% of MHD is bound to serum proteins, predominantly to albumin. Binding is independent of the serum concentration within the therapeutically relevant range. Oxcarbazepine and MHD do not bind to alpha-1-acid glycoprotein.
Metabolism And Excretion
Oxcarbazepine is rapidly reduced by cytosolic enzymes in the liver to its 10-monohydroxy metabolite, MHD, which is primarily responsible for the pharmacological effect of Trileptal. MHD is metabolized further by conjugation with glucuronic acid. Minor amounts (4% of the dose) are oxidized to the pharmacologically inactive 10,11-dihydroxy metabolite (DHD).
Oxcarbazepine is cleared from the body mostly in the form of metabolites which are predominantly excreted by the kidneys. More than 95% of the dose appears in the urine, with less than 1% as unchanged oxcarbazepine. Fecal excretion accounts for less than 4% of the administered dose. Approximately 80% of the dose is excreted in the urine either as glucuronides of MHD (49%) or as unchanged MHD (27%); the inactive DHD accounts for approximately 3% and conjugates of MHD and oxcarbazepine account for 13% of the dose.
The half-life of the parent is about two hours, while the half-life of MHD is about nine hours.
The pharmacokinetics and metabolism of oxcarbazepine and MHD were evaluated in healthy volunteers and hepaticallyimpaired subjects after a single 900-mg oral dose. Mild-to-moderate hepatic impairment did not affect the pharmacokinetics of oxcarbazepine and MHD. No dose adjustment for Trileptal is recommended in patients with mild-tomoderate hepatic impairment. The pharmacokinetics of oxcarbazepine and MHD have not been evaluated in severe hepatic impairment and, therefore, caution should be exercised when dosing severely impaired patients [see DOSAGE AND ADMINISTRATION].
There is a linear correlation between creatinine clearance and the renal clearance of MHD. When Trileptal is administered as a single 300-mg dose in renally-impaired patients (creatinine clearance < 30 mL/min), the elimination half-life of MHD is prolonged to 19 hours, with a two-fold increase in AUC. Dose adjustment for Trileptal is recommended in these patients [see Use In Specific Populations and see DOSAGE AND ADMINISTRATION].
Weight-adjusted MHD clearance decreases as age and weight increases, approaching that of adults. The mean weight-adjusted clearance in children 2 years- < 4 years of age is approximately 80% higher on average than that of adults. Therefore, MHD exposure in these children is expected to be about one-half that of adults when treated with a similar weight-adjusted dose. The mean weight-adjusted clearance in children 4–12 years of age is approximately 40% higher on average than that of adults. Therefore, MHD exposure in these children is expected to be about three-quarters that of adults when treated with a similar weight-adjusted dose. As weight increases, for patients 13 years of age and above, the weight-adjusted MHD clearance is expected to reach that of adults.
Due to physiological changes during pregnancy, MHD plasma levels may gradually decrease throughout pregnancy [see Use In Specific Populations]
Following administration of single (300 mg) and multiple (600 mg/day) doses of Trileptal to elderly volunteers (60-82 years of age), the maximum plasma concentrations and AUC values of MHD were 30%-60% higher than in younger volunteers (18-32 years of age). Comparisons of creatinine clearance in young and elderly volunteers indicate that the difference was due to age-related reductions in creatinine clearance.
No gender-related pharmacokinetic differences have been observed in children, adults, or the elderly.
No specific studies have been conducted to assess what effect, if any, race may have on the disposition of oxcarbazepine.
Oxcarbazepine can inhibit CYP2C19 and induce CYP3A4/5 with potentially important effects on plasma concentrations of other drugs. In addition, several AEDs that are cytochrome P450 inducers can decrease plasma concentrations of oxcarbazepine and MHD.
Oxcarbazepine was evaluated in human liver microsomes to determine its capacity to inhibit the major cytochrome P450 enzymes responsible for the metabolism of other drugs. Results demonstrate that oxcarbazepine and its pharmacologically active 10-monohydroxy metabolite (MHD) have little or no capacity to function as inhibitors for most of the human cytochrome P450 enzymes evaluated (CYP1A2, CYP2A6, CYP2C9, CYP2D6, CYP2E1, CYP4A9 and CYP4A11) with the exception of CYP2C19 and CYP3A4/5. Although inhibition of CYP3A4/5 by oxcarbazepine and MHD did occur at high concentrations, it is not likely to be of clinical significance. The inhibition of CYP2C19 by oxcarbazepine and MHD, is clinically relevant.
In vitro, the UDP-glucuronyl transferase level was increased, indicating induction of this enzyme. Increases of 22% with MHD and 47% with oxcarbazepine were observed. As MHD, the predominant plasma substrate, is only a weak inducer of UDP-glucuronyl transferase, it is unlikely to have an effect on drugs that are mainly eliminated by conjugation through UDPglucuronyl transferase (e.g., valproic acid, lamotrigine).
In addition, oxcarbazepine and MHD induce a subgroup of the cytochrome P450 3A family (CYP3A4 and CYP3A5) responsible for the metabolism of dihydropyridine calcium antagonists, oral contraceptives and cyclosporine resulting in a lower plasma concentration of these drugs.
As binding of MHD to plasma proteins is low (40%), clinically significant interactions with other drugs through competition for protein binding sites are unlikely.
For in vivo drug interactions [see DRUG INTERACTIONS].
The effectiveness of Trileptal as adjunctive and monotherapy for partial seizures in adults, and as adjunctive therapy in children aged 2-16 years was established in seven multicenter, randomized, controlled trials.
The effectiveness of Trileptal as monotherapy for partial seizures in children aged 4-16 years was determined from data obtained in the studies described, as well as by pharmacokinetic/pharmacodynamic considerations.
Trileptal Monotherapy Trials
Four randomized, controlled, double-blind, multicenter trials, conducted in a predominately adult population, demonstrated the efficacy of Trileptal as monotherapy. Two trials compared Trileptal to placebo and two trials used a randomized withdrawal design to compare a high dose (2400 mg) with a low dose (300 mg) of Trileptal, after substituting Trileptal 2400 mg/day for one or more antiepileptic drugs (AEDs). All doses were administered on a twice-a-day schedule. A fifth randomized, controlled, rater-blind, multicenter study, conducted in a pediatric population, failed to demonstrate a statistically significant difference between low and high dose Trileptal treatment groups.
One placebo-controlled trial was conducted in 102 patients (11-62 years of age) with refractory partial seizures who had completed an inpatient evaluation for epilepsy surgery. Patients had been withdrawn from all AEDs and were required to have 2-10 partial seizures within 48 hours prior to randomization. Patients were randomized to receive either placebo or Trileptal given as 1500 mg/day on Day 1 and 2400 mg/day thereafter for an additional nine days, or until one of the following three exit criteria occurred: 1) the occurrence of a fourth partial seizure, excluding Day 1, 2) two new-onset secondarily generalized seizures, where such seizures were not seen in the one-year period prior to randomization, or 3) occurrence of serial seizures or status epilepticus. The primary measure of effectiveness was a between-group comparison of the time to meet exit criteria. There was a statistically significant difference in favor of Trileptal (see Figure 1), p=0.0001.
Figure 1 : Kaplan-Meier
Estimates of Exit Rate by Treatment Group
The second placebo-controlled trial was conducted in 67 untreated patients (8-69 years of age) with newly-diagnosed and recent-onset partial seizures. Patients were randomized to placebo or Trileptal, initiated at 300 mg twice a day and titrated to 1200 mg/day (given as 600 mg twice a day) in six days, followed by maintenance treatment for 84 days. The primary measure of effectiveness was a between-group comparison of the time to first seizure. The difference between the two treatments was statistically significant in favor of Trileptal (see Figure 2), p=0.046.
Figure 2 : Kaplan-Meier
Estimates of First Seizure Event Rate by Treatment Group
A third trial substituted Trileptal monotherapy at 2400 mg/day for carbamazepine in 143 patients (12-65 years of age) whose partial seizures were inadequately controlled on carbamazepine (CBZ) monotherapy at a stable dose of 800 to 1600 mg/day, and maintained this Trileptal dose for 56 days (baseline phase). Patients who were able to tolerate titration of Trileptal to 2400 mg/day during simultaneous carbamazepine withdrawal were randomly assigned to either 300 mg/day of Trileptal or 2400 mg/day Trileptal. Patients were observed for 126 days or until one of the following four exit criteria occurred: 1) a doubling of the 28-day seizure frequency compared to baseline, 2) a two-fold increase in the highest consecutive two-day seizure frequency during baseline, 3) a single generalized seizure if none had occurred during baseline, or 4) a prolonged generalized seizure. The primary measure of effectiveness was a between-group comparison of the time to meet exit criteria. The difference between the curves was statistically significant in favor of the Trileptal 2400 mg/day group (see Figure 3), p=0.0001.
Figure 3 : Kaplan-Meier
Estimates of Exit Rate by Treatment Group
Another monotherapy substitution trial was conducted in 87 patients (11-66 years of age) whose seizures were inadequately controlled on one or two AEDs. Patients were randomized to either Trileptal 2400 mg/day or 300 mg/day and their standard AED regimen(s) were eliminated over the first six weeks of double-blind therapy. Double-blind treatment continued for another 84 days (total double-blind treatment of 126 days) or until one of the four exit criteria described for the previous study occurred. The primary measure of effectiveness was a between-group comparison of the percentage of patients meeting exit criteria. The results were statistically significant in favor of the Trileptal 2400 mg/day group (14/34; 41.2%) compared to the Trileptal 300 mg/day group (42/45; 93.3%) (p < 0.0001). The time to meeting one of the exit criteria was also statistically significant in favor of the Trileptal 2400 mg/day group (see Figure 4), p=0.0001.
Figure 4 : Kaplan-Meier
Estimates of Exit Rate by Treatment Group
A monotherapy trial was conducted in 92 pediatric patients (1 month to 16 years of age) with inadequately-controlled or new-onset partial seizures. Patients were hospitalized and randomized to either Trileptal 10 mg/kg/day or were titrated up to 40-60 mg/kg/day within three days while withdrawing the previous AED on the second day of Trileptal therapy. Seizures were recorded through continuous video-EEG monitoring from Day 3 to Day 5. Patients either completed the 5day treatment or met one of the two exit criteria: 1) three study-specific seizures (i.e., electrographic partial seizures with a behavioral correlate), 2) a prolonged study-specific seizure. The primary measure of effectiveness was a between-group comparison of the time to meet exit criteria in which the difference between the curves was not statistically significant (p=0.904). The majority of patients from both dose groups completed the 5-day study without exiting.
Although this study failed to demonstrate an effect of oxcarbazepine as monotherapy in pediatric patients, several design elements, including the short treatment and assessment period, the absence of a true placebo, and the likely persistence of plasma levels of previously administered AEDs during the treatment period, make the results uninterpretable. For this reason, the results do not undermine the conclusion, based on pharmacokinetic/pharmacodynamic considerations, that oxcarbazepine is effective as monotherapy in pediatric patients 4 years old and older.
Trileptal Adjunctive Therapy Trials
The effectiveness of Trileptal as an adjunctive therapy for partial seizures was established in two multicenter, randomized, double-blind, placebo-controlled trials, one in 692 patients (15-66 years of age) and one in 264 pediatric patients (3-17 years of age), and in one multicenter, rater-blind, randomized, age-stratified, parallel-group study comparing two doses of oxcarbazepine in 128 pediatric patients (1 month to < 4 years of age).
Patients in the two placebo-controlled trials were on 1-3 concomitant AEDs. In both of the trials, patients were stabilized on optimum dosages of their concomitant AEDs during an 8-week baseline phase. Patients who experienced at least 8 (minimum of 1-4 per month) partial seizures during the baseline phase were randomly assigned to placebo or to a specific dose of Trileptal in addition to their other AEDs.
In these studies, the dose was increased over a two-week period until either the assigned dose was reached, or intolerance prevented increases. Patients then entered a 14- (pediatrics) or 24-week (adults) maintenance period.
In the adult trial, patients received fixed doses of 600, 1200 or 2400 mg/day. In the pediatric trial, patients received maintenance doses in the range of 30-46 mg/kg/day, depending on baseline weight. The primary measure of effectiveness in both trials was a between-group comparison of the percentage change in partial seizure frequency in the double-blind treatment phase relative to baseline phase. This comparison was statistically significant in favor of Trileptal at all doses tested in both trials (p=0.0001 for all doses for both trials). The number of patients randomized to each dose, the median baseline seizure rate, and the median percentage seizure rate reduction for each trial are shown in Table 8. It is important to note that in the high-dose group in the study in adults, over 65% of patients discontinued treatment because of adverse events; only 46 (27%) of the patients in this group completed the 28-week study [see ADVERSE REACTIONS], an outcome not seen in the monotherapy studies.
Table 8 : Summary of
Percentage Change in Partial Seizure Frequency from Baseline for
Placebo-Controlled Adjunctive Therapy Trials
|Trial||Treatment Group||N||Baseline Median||Median %|
|2 (adults)||Trileptal 2400 mg/day||174||10.0||49.91|
|Trileptal 1200 mg/day||177||9.8||40.21|
|Trileptal 600 mg/day||168||9.6||26.41|
|1p=0.0001; * = # per 28 days|
Subset analyses of the antiepileptic efficacy of Trileptal with regard to gender in these trials revealed no important differences in response between men and women. Because there were very few patients over the age of 65 in controlled trials, the effect of the drug in the elderly has not been adequately assessed.
The third adjunctive therapy trial enrolled 128 pediatric patients (1 month to < 4 years of age) with inadequately-controlled partial seizures on 1-2 concomitant AEDs. Patients who experienced at least 2 study-specific seizures (i.e., electrographic partial seizures with a behavioral correlate) during the 72-hour baseline period were randomly assigned to either Trileptal 10 mg/kg/day or were titrated up to 60 mg/kg/day within 26 days. Patients were maintained on their randomized target dose for 9 days and seizures were recorded through continuous video-EEG monitoring during the last 72 hours of the maintenance period. The primary measure of effectiveness in this trial was a between-group comparison of the change in seizure frequency per 24 hours compared to the seizure frequency at baseline. For the entire group of patients enrolled, this comparison was statistically significant in favor of Trileptal 60 mg/kg/day. In this study, there was no evidence that Trileptal was effective in patients below the age of 2 years (N=75).
Last reviewed on RxList: 2/14/2014
This monograph has been modified to include the generic and brand name in many instances.
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