Lamotrigine 200 mg Tablet, 1,000-count — NDC 46708-277-91 (Billing 46708-0277-91)

12. CLINICAL PHARMACOLOGY 12.1. Mechanism of Action The precise mechanism(s) by which lamotrigine exerts its anticonvulsant action are unknown.

In animal models designed to detect anticonvulsant activity, lamotrigine was effective in preventing seizure spread in the maximum electroshock (MES) and pentylenetetrazol (scMet) tests, and prevented seizures in the visually and electrically evoked after-discharge (EEAD) tests for antiepileptic activity. Lamotrigine also displayed inhibitory properties in the kindling model in rats both during kindling development and in the fully kindled state. The relevance of these models to human epilepsy, however, is not known.

One proposed mechanism of action of lamotrigine, the relevance of which remains to be established in humans, involves an effect on sodium channels. In vitro pharmacological studies suggest that lamotrigine inhibits voltage-sensitive sodium channels, thereby stabilizing neuronal membranes and consequently modulating presynaptic transmitter release of excitatory amino acids (e.g., glutamate and aspartate). Effect of Lamotrigine on N-Methyl d-Aspartate-Receptor-Mediated Activity Lamotrigine did not inhibit N-methyl d-aspartate (NMDA)-induced depolarizations in rat cortical slices or NMDA-induced cyclic GMP formation in immature rat cerebellum, nor did lamotrigine displace compounds that are either competitive or noncompetitive ligands at this glutamate receptor complex (CNQX, CGS, TCHP).

The IC 50 for lamotrigine effects on NMDA-induced currents (in the presence of 3 µM of glycine) in cultured hippocampal neurons exceeded 100 µM. The mechanisms by which lamotrigine exerts its therapeutic action in bipolar disorder have not been established. 12.2.

Pharmacodynamics Folate Metabolism In vitro, lamotrigine inhibited dihydrofolate reductase, the enzyme that catalyzes the reduction of dihydrofolate to tetrahydrofolate. Inhibition of this enzyme may interfere with the biosynthesis of nucleic acids and proteins. When oral daily doses of lamotrigine were given to pregnant rats during organogenesis, fetal, placental, and maternal folate concentrations were reduced.

Significantly reduced concentrations of folate are associated with teratogenesis [see Use in Specific Populations (8.1)] . Folate concentrations were also reduced in male rats given repeated oral doses of lamotrigine. Reduced concentrations were partially returned to normal when supplemented with folinic acid.

Accumulation in Kidneys Lamotrigine accumulated in the kidney of the male rat, causing chronic progressive nephrosis, necrosis, and mineralization. These findings are attributed to α-2 microglobulin, a species- and sex-specific protein that has not been detected in humans or other animal species. Melanin Binding Lamotrigine binds to melanin-containing tissues, e.g., in the eye and pigmented skin.

It has been found in the uveal tract up to 52 weeks after a single dose in rodents. Cardiovascular In dogs, lamotrigine is extensively metabolized to a 2-N-methyl metabolite. This metabolite causes dose-dependent prolongations of the PR interval, widening of the QRS complex, and, at higher doses, complete AV conduction block.

Similar cardiovascular effects are not anticipated in humans because only trace amounts of the 2-N-methyl metabolite (<0.6% of lamotrigine dose) have been found in human urine [see Clinical Pharmacology (12.3)] . However, it is conceivable that plasma concentrations of this metabolite could be increased in patients with a reduced capacity to glucuronidate lamotrigine (e.g., in patients with liver disease, patients taking concomitant medications that inhibit glucuronidation). 12.3.

Pharmacokinetics The pharmacokinetics of lamotrigine have been studied in subjects with epilepsy, healthy young and elderly volunteers, and volunteers with chronic renal failure. Lamotrigine pharmacokinetic parameters for adult and pediatric subjects and healthy normal volunteers are summarized in Tables 14 and 16. Table 14 Mean… [Excerpted — this section continues on DailyMed.]

12.1. Mechanism of Action The precise mechanism(s) by which lamotrigine exerts its anticonvulsant action are unknown. In animal models designed to detect anticonvulsant activity, lamotrigine was effective in preventing seizure spread in the maximum electroshock (MES) and pentylenetetrazol (scMet) tests, and prevented seizures in the visually and electrically evoked after-discharge (EEAD) tests for antiepileptic activity.

Lamotrigine also displayed inhibitory properties in the kindling model in rats both during kindling development and in the fully kindled state. The relevance of these models to human epilepsy, however, is not known. One proposed mechanism of action of lamotrigine, the relevance of which remains to be established in humans, involves an effect on sodium channels.

In vitro pharmacological studies suggest that lamotrigine inhibits voltage-sensitive sodium channels, thereby stabilizing neuronal membranes and consequently modulating presynaptic transmitter release of excitatory amino acids (e.g., glutamate and aspartate). Effect of Lamotrigine on N-Methyl d-Aspartate-Receptor-Mediated Activity Lamotrigine did not inhibit N-methyl d-aspartate (NMDA)-induced depolarizations in rat cortical slices or NMDA-induced cyclic GMP formation in immature rat cerebellum, nor did lamotrigine displace compounds that are either competitive or noncompetitive ligands at this glutamate receptor complex (CNQX, CGS, TCHP).

The IC 50 for lamotrigine effects on NMDA-induced currents (in the presence of 3 µM of glycine) in cultured hippocampal neurons exceeded 100 µM. The mechanisms by which lamotrigine exerts its therapeutic action in bipolar disorder have not been established.

12.3. Pharmacokinetics The pharmacokinetics of lamotrigine have been studied in subjects with epilepsy, healthy young and elderly volunteers, and volunteers with chronic renal failure. Lamotrigine pharmacokinetic parameters for adult and pediatric subjects and healthy normal volunteers are summarized in Tables 14 and 16.

Table 14 Mean Pharmacokinetic Parameters a in Healthy Volunteers and Adult Subjects with Epilepsy Adult Study Population Number of Subjects T max : Time of Maximum Plasma Concentration (h) t ½ : Elimination Half-life (h) CL/F: Apparent Plasma Clearance (mL/min/kg) Healthy volunteers taking no other medications: Single-dose Lamotrigine Tablets Multiple-dose Lamotrigine Tablets 179 36 2.2 (0.25 to 12) 1.7 (0.5 to 4) 32.8 (14 to 103) 25.4 (11.6 to 61.6) 0.44 (0.12 to 1.1) 0.58 (0.24 to 1.15) Healthy volunteers taking valproate: Single-dose Lamotrigine Tablets Multiple-dose Lamotrigine Tablets 6 18 1.8 (1 to 4) 1.9 (0.5 to 3.5) 48.3 (31.5 to 88.6) 70.3 (41.9 to 113.5) 0.3 (0.14 to 0.42) 0.18 (0.12 to 0.33) Subjects with epilepsy taking valproate only: Single-dose Lamotrigine Tablets 4 4.8 (1.8 to 8.4) 58.8 (30.5 to 88.8) 0.28 (0.16 to 0.4) Subjects with epilepsy taking carbamazepine, phenytoin, phenobarbital, or primidone b plus valproate: Single-dose Lamotrigine Tablets 25 3.8 (1 to 10) 27.2 (11.2 to 51.6) 0.53 (0.27 to 1.04) Subjects with epilepsy taking carbamazepine, phenytoin, phenobarbital, or primidone b : Single-dose Lamotrigine Tablets Multiple-dose Lamotrigine Tablets 24 17 2.3 (0.5 to 5) 2 (0.75 to 5.93) 14.4 (6.4 to 30.4) 12.6 (7.5 to 23.1) 1.1 (0.51 to 2.22) 1.21 (0.66 to 1.82) a The majority of parameter means determined in each study had coefficients of variation between 20% and 40% for half-life and CL/F and between 30% and 70% for T max .

The overall mean values were calculated from individual study means that were weighted based on the number of volunteers/ subjects in each study. The numbers in parentheses below each parameter mean represent the range of individual volunteer/ subject values across studies. b Carbamazepine, phenytoin, phenobarbital and primidone have been shown to increase the apparent clearance of lamotrigine. Estrogen-containing oral contraceptives and other drugs, such as rifampin and protease inhibitors lopinavir/ritonavir and atazanavir/ritonavir, that induce lamotrigine glucuronidation have also been shown to increase the apparent clearance of lamotrigine [see Drug Interactions (7)] .

Absorption Lamotrigine is rapidly and completely absorbed after oral administration with negligible first-pass metabolism (absolute bioavailability is 98%). The bioavailability is not affected by food. Peak plasma concentrations occur anywhere from 1.4 to 4.8 hours following drug administration.

Dose Proportionality In healthy volunteers not receiving any other medications and given single doses, the plasma concentrations of lamotrigine increased in direct proportion to the dose administered over the range of 50 to 400 mg. In 2 small studies (n = 7 and 8) of patients with epilepsy who were maintained on other AEDs, there also was a linear relationship between dose and lamotrigine plasma concentrations at steady state following doses of 50 to 350 mg twice daily. Distribution Estimates of the mean apparent volume of distribution (Vd/F) of lamotrigine following oral administration ranged from 0.9 to

1.3L/kg. Vd/F is independent of dose and is similar following single and multiple doses in both patients with epilepsy and in healthy volunteers. Protein Binding Data from in vitro studies indicate that lamotrigine is approximately 55% bound to human plasma proteins at plasma lamotrigine concentrations from 1 to 10 mcg/mL (10 mcg/mL is 4 to 6 times the trough plasma concentration observed in the controlled efficacy trials).

Because lamotrigine is not highly bound to plasma proteins, clinically significant interactions with other drugs through competition for protein binding sites are unlikely. The bi… [Excerpted — this section continues on DailyMed.]

12.2. Pharmacodynamics Folate Metabolism In vitro, lamotrigine inhibited dihydrofolate reductase, the enzyme that catalyzes the reduction of dihydrofolate to tetrahydrofolate. Inhibition of this enzyme may interfere with the biosynthesis of nucleic acids and proteins.

When oral daily doses of lamotrigine were given to pregnant rats during organogenesis, fetal, placental, and maternal folate concentrations were reduced. Significantly reduced concentrations of folate are associated with teratogenesis [see Use in Specific Populations (8.1)] . Folate concentrations were also reduced in male rats given repeated oral doses of lamotrigine.

Reduced concentrations were partially returned to normal when supplemented with folinic acid. Accumulation in Kidneys Lamotrigine accumulated in the kidney of the male rat, causing chronic progressive nephrosis, necrosis, and mineralization. These findings are attributed to α-2 microglobulin, a species- and sex-specific protein that has not been detected in humans or other animal species.

Melanin Binding Lamotrigine binds to melanin-containing tissues, e.g., in the eye and pigmented skin. It has been found in the uveal tract up to 52 weeks after a single dose in rodents. Cardiovascular In dogs, lamotrigine is extensively metabolized to a 2-N-methyl metabolite.

This metabolite causes dose-dependent prolongations of the PR interval, widening of the QRS complex, and, at higher doses, complete AV conduction block. Similar cardiovascular effects are not anticipated in humans because only trace amounts of the 2-N-methyl metabolite (<0.6% of lamotrigine dose) have been found in human urine [see Clinical Pharmacology (12.3)] . However, it is conceivable that plasma concentrations of this metabolite could be increased in patients with a reduced capacity to glucuronidate lamotrigine (e.g., in patients with liver disease, patients taking concomitant medications that inhibit glucuronidation).

14. CLINICAL STUDIES 14.1. Epilepsy Monotherapy with Lamotrigine Tablets in Adults with Partial-Onset Seizures Already Receiving Treatment with Carbamazepine, Phenytoin, Phenobarbital, or Primidone as the Single Antiepileptic Drug The effectiveness of monotherapy with lamotrigine tablets were established in a multicenter, double-blind clinical trial enrolling 156 adult outpatients with partial-onset seizures.

The patients experienced at least 4 simple partial-onset, complex partial-onset, and/or secondarily generalized seizures during each of 2 consecutive 4-week periods while receiving carbamazepine or phenytoin monotherapy during baseline. Lamotrigine tablets (target dose of 500 mg/day) or valproate (1,000 mg/day) was added to either carbamazepine or phenytoin monotherapy over a 4-week period. Patients were then converted to monotherapy with lamotrigine tablets or valproate during the next 4 weeks, then continued on monotherapy for an additional 12-week period.

Trial endpoints were completion of all weeks of trial treatment or meeting an escape criterion. Criteria for escape relative to baseline were: (1) doubling of average monthly seizure count, (2) doubling of highest consecutive 2-day seizure frequency, (3) emergence of a new seizure type (defined as a seizure that did not occur during the 8-week baseline) that is more severe than seizure types that occur during study treatment, or (4) clinically significant prolongation of generalized tonic-clonic seizures. The primary efficacy variable was the proportion of patients in each treatment group who met escape criteria.

The percentages of patients who met escape criteria were 42% (32/76) in the group receiving lamotrigine tablet and 69% (55/80) in the valproate group. The difference in the percentage of patients meeting escape criteria was statistically significant ( P = 0.0012) in favor of lamotrigine tablets. No differences in efficacy based on age, sex, or race were detected.

Patients in the control group were intentionally treated with a relatively low dose of valproate; as such, the sole objective of this trial was to demonstrate the effectiveness and safety of monotherapy with lamotrigine tablets, and cannot be interpreted to imply the superiority of lamotrigine tablets to an adequate dose of valproate. Adjunctive Therapy with Lamotrigine Tablets in Adults with Partial-Onset Seizures The effectiveness of lamotrigine tablets as adjunctive therapy (added to other AEDs) was initially established in 3 pivotal, multicenter, placebo-controlled, double-blind clinical trials in 355 adults with refractory partial-onset seizures.

The patients had a history of at least 4 partial-onset seizures per month in spite of receiving 1 or more AEDs at therapeutic concentrations and, in 2 of the trials, were observed on their established AED regimen during baselines that varied between 8 to 12 weeks. In the third trial, patients were not observed in a prospective baseline. In patients continuing to have at least 4 seizures per month during the baseline, lamotrigine tablets or placebo was then added to the existing therapy.

In all 3 trials, change from baseline in seizure frequency was the primary measure of effectiveness. The results given below are for all partial-onset seizures in the intent-to-treat population (all patients who received at least 1 dose of treatment) in each trial, unless otherwise indicated. The median seizure frequency at baseline was 3 per week while the mean at baseline was 6.6 per week for all patients enrolled in efficacy trials.

One trial (n = 216) was a double-blind, placebo-controlled, parallel trial consisting of a 24-week treatment period. Patients could not be on more than 2 other anticonvulsants and valproate was not allowed. Patients were randomized to receive placebo, a target dose of 300 mg/day of lamotrigine tablets, or a target dose of 500 mg/day of lamotrigine tablets.

The median reductions in the frequency of all partial-onset seizures relative to bas… [Excerpted — this section continues on DailyMed.]

13. NONCLINICAL TOXICOLOGY 13.1. Carcinogenesis, Mutagenesis, Impairment of Fertility No evidence of carcinogenicity was seen in mouse or rat following oral administration of lamotrigine for up to 2 years at doses up to 30 mg/kg/day and 10 to 15 mg/kg/day in mouse and rat, respectively.

The highest doses tested are less than the human dose of 400 mg/day on a body surface area (mg/m 2 ) basis. Lamotrigine was negative in in vitro gene mutation (Ames and mouse lymphoma tk ) assays and in clastogenicity (in vitro human lymphocyte and in vivo rat bone marrow) assays. No evidence of impaired fertility was detected in rats given oral doses of lamotrigine up to 20 mg/kg/day.

The highest dose tested is less than the human dose of 400 mg/day on a mg/m 2 basis.