New and investigational antiepilepsy drugs

Double-blind, placebo-controlled study of topiramate in patients with refractory partial epilepsy

The efficacy and safety of topiramate 400 mg/day as adjunctive therapy to traditional antieleptic drugs for partial onset seizures with or without secondary generalization were assessed in a double-blind, parallel-group, placebo-controlled trial. Forty-seven patients with at least one seizure per week during an 8 week baseline were randomly assigned to topiramate (N = 23) or placebo (N = 24) double-blind treatment for a 3 week titration and an 8 week stabilization period. Median percent reduction from baseline in monthly seizure frequency during the double-blind phase was not significantly greater in the topiramate group than in the placebo group (41% vs. 1%; P = 0.065). Nevertheless, other efficacy variables evidenced statistically significant differences in favor of topiramate: a greater number of treatment responders (> or = 50% reduction in seizures; 35% vs. 8%; P = 0.033); better investigator (P = 0.002) and patient (P = 0.021) global assessments; and greater reductions in secondarily generalized seizures compared to placebo (P = 0.002). The most commonly reported topiramate treatment-emergent adverse events were somnolence, fatigue, abnormal vision, weight decrease, and anxiety. Most adverse events were mild or moderate in severity. Among 7 withdrawals due to limiting adverse events, 6 were CNS-related (in 5 topiramate-treated patients). Results of this trial strongly suggest that topiramate 400 mg/day is effective and well tolerated in the treatment of refractory partial epilepsy.

Steady-state pharmacokinetics of topiramate and carbamazepine in patients with epilepsy during monotherapy and concomitant therapy

PURPOSE

We studied the steady-state pharmacokinetic profile of topiramate (TPM) as a function of dose and the effects of comedication with carbamazepine (CBZ).

METHODS

We enrolled 12 patients with partial epilepsy receiving chronic stable doses of CBZ 300-800 mg every 8 h. In a 6-week period, TPM was added and doses were increased at approximately 2-week intervals from 100 to 200 to 400 mg every 12 h and stabilized at the highest tolerated dose to as high as 400 mg every 12 h. CBZ was tapered in the next 4 weeks when possible, and TPM was maintained as monotherapy at the highest stabilized dose for 2 more weeks. Plasma and urine samples were collected before TPM dosing, after each TPM dose increase, and during TPM monotherapy.

RESULTS

Dose-normalized results (n = 10) for TPM area under the curve from 0 to 12 h (AUC(0-12)), Cmin(0), and Cavg indicated that TPM exhibits linear plasma pharmacokinetics over the dose range of 100- to 400-mg every 12 h when administered with CBZ. Mean TPM AUC(0-12), Cmax, Cmin(0), and Cavg values were approximately 40% lower during CBZ treatment as compared with those during TPM monotherapy (n = 3). TPM oral and nonrenal clearance rates were approximately two- to threefold higher, whereas TPM renal clearance was unchanged during concomitant CBZ treatment (n = 3). There were no significant changes in total and unbound CBZ and CBZ-epoxide (CBZ-E) pharmacokinetics during TPM administration (n = 10). TPM pharmacokinetics during concomitant CBZ treatment were significantly different from those during TPM monotherapy, suggesting that metabolic clearance of TPM increases when CBZ is coadministered.

CONCLUSIONS

When CBZ is reduced or discontinued, TPM doses may need to be lowered to maintain equivalent plasma concentrations. Adjusting the CBZ dose for pharmacokinetic reasons when TPM is administered as adjunctive treatment does not appear to be necessary.

Double-blind, placebo-controlled trial of topiramate (600 mg daily) for the treatment of refractory partial epilepsy

PURPOSE

We wished to evaluate adjunctive therapy for partial-onset seizures with topiramate (TPM) for efficacy and safety in a double-blind, placebo-controlled, randomized, parallel-group study.

METHODS

Sixty outpatients with epilepsy (47 men and 13 women, mean age 32.9 years) were studied. All had a documented history of partial-onset seizures with or without secondarily generalized seizures. After an 8-week baseline during which patients had at least one seizure per week, 30 patients each were randomized to TPM 300 mg twice daily (b.i.d.) or placebo for 12 weeks.

RESULTS

TPM was significantly superior to placebo, as indicated by all efficacy assessments: greater median percent reduction from baseline in the average monthly seizure rate (46 vs. -12%, p = 0.004); greater number of treatment responders (patients with > or = 50% reduction in seizure rate) (47 vs. 10%, p = 0.001), and better investigator (p = 0.002) and patient (p = 0.010) global assessments of treatment. Among TPM-treated patients, the most commonly reported adverse events (AE) were headache, somnolence, fatigue, dizziness, and abnormal thinking. Most AE were mild or moderate in severity.

CONCLUSIONS

The results of the present trial indicate that TPM 600 mg/day is effective in the treatment of refractory partial-onset seizures with or without secondarily generalized seizures.

International experience with tiagabine add-on therapy

Tiagabine (TGB) hydrochloride is a novel antiepileptic drug (AED) that is a potent and specific inhibitor of gamma-aminobutyric acid (GABA) uptake into glial and neuronal elements. In accordance with medical and regulatory standards, the clinical development program for TGB as an AED has assessed the value of TGB in add-on treatment, focusing mainly on partial seizures, including secondarily generalized seizures. Five add-on, placebo-controlled trials and six noncomparative, open-label, long-term multicenter trials have been or are being conducted in Australia, Europe, and the U.S.A. The results of these trials, involving 2,261 patients, indicate that TGB has efficacy as add-on therapy in patients with epilepsy difficult to control with existing AEDs. Efficacy of TGB is also sustained with long-term treatment. A clear dose-response has been demonstrated, and the minimal effective dose level is 30 mg. TGB is also tolerated, and with long-term therapy no new or more severe types of adverse events develop. These studies have included a wide age range of patients, including adolescents and the elderly.