Over 2 decades, carbamazepine has become a well-established, off-label alternative to lithium for treating acute mania. In December, the FDA approved an extended-release form of the anticonvulsant to treat type I bipolar disorder (Table 1).
This article addresses clinical use of extended-release capsules of carbamazepine (ERC-CBZ) and their safety, tolerability, and potential to interact with other medications.
Table 1
Extended-release capsules
of carbamazepine:
Fast facts
| Brand name: Equetro |
| Class: Anticonvulsant |
| FDA-approved indication: Bipolar mania |
| Manufacturer: Shire Pharmaceuticals Group |
| Dosing form: 100-, 200-, and 300-mg capsules |
| Recommended dosage: Manufacturer recommends starting at 400 mg/d in two divided doses.* Adjust dosage in 200-mg increments to achieve optimal response. Dosages >1,600 mg/d have not been studied. |
| *The author recommends starting at 200 mg/d using once-daily, nighttime dosing and titrating slowly based on tolerability and efficacy, continuing with nighttime dosing only. |
PHARMACOKINETICS
Because ERC-CBZ and carbamazepine yield similar molecules, the extended- and immediate-release forms have similar pharmacodynamic properties. There are notable pharmacokinetic differences, however.
With chronic use, carbamazepine autoinduces cytochrome P-450 (CYP) 3A4 hepatic enzymes. These enzymes rapidly break down carbamazepine to its active 10, 11-epoxide metabolite and the epoxide to the inactive diol. Because this sequence shortens carbamazepine’s half-life considerably—from 35 to 40 hours to 12 to 17 hours after 2 to 3 weeks of use—multiple daily dosing and minor dosage increases often are needed to maintain carbamazepine blood levels. Also, with immediate-release carbamazepine’s peak/trough variations, transient side effects such as ataxia, dizziness, or diplopia may emerge 2 to 3 hours after dosing once steady state is reached.
By contrast, ERC-CBZ should be more tolerable and easier to use because it smooths out these variations. Although studies of ERC-CBZ in mania have examined twice-daily dosing, using once-nightly dosing instead (starting at 200 mg) will harness carbamazepine’s sedative and other side effects to promote sleep onset, and lower levels throughout the day will further increase its tolerability.1 Patients who experience breakthrough afternoon or evening manic symptoms with once-nightly dosing can be returned to twice-daily dosing.
EFFICACY IN BIPOLAR DISORDER
ERC-CBZ has shown efficacy for treating bipolar disorder in three studies,2,3,4 including two large double-blind, placebo-controlled, multi-center trials that followed patients with type I bipolar disorder with current manic or mixed episodes.
In the first trial,2 204 patients received ERC-CBZ, 400 to 1,600 mg/d (mean±SD daily dosage 756.4±413.4 mg/d, mean plasma level 8.9 μg/mL), or placebo for 3 weeks. Young Mania Rating Scale (YMRS) scores decreased 50% in 41.5% of the treatment group and in 22.4% of the placebo group. Hamilton Rating Scale for Depression (HAM-D) scores decreased more in the ERC-CBZ group, but the difference was not clinically significant.
In a second trial of 239 patients,3 YMRS scores fell 50% across 3 weeks in 60.8% of those taking ERC-CBZ, 400 to 1,600 mg/d (mean±SD dosage 642±369.2 mg/d), compared with 28.7% of placebotreated patients. HAM-D total scores also improved significantly in ERC-CBZ-treated patients compared with the placebo group in a subanalysis of 188 intent-to-treat patients with a manic episode.
In a 6-month extension following 92 patients from two double-blind trials,4 mean total YMRS scores decreased among former placebo group patients switched to open-label ERC-CBZ, 200 to 1,600 mg/d (mean dosage 938 mg, mean serum level 6.6 μg/mL). Patients who had taken ERC-CBZ during the acute trial saw little change in YMRS scores during continued ERC-CBZ treatment, except in the second month. At end point, however, YMRS scores fell further for both treatment groups. HAM-D total scores differed little across 6 months, but 54 patients with mixed states maintained significant reductions.
Maintenance therapy. In many studies, carbamazepine has compared favorably with lithium for long-term bipolar maintenance in some patients. Consider patients who respond well to acute carbamazepine therapy for continuation treatment with ERC-CBZ. Patients who may be most likely to respond to carbamazepine therapy include those with:
- type II bipolar disorder
- substance abuse comorbidity
- mood-incongruent delusions
- no family history of bipolar illness among first-degree relatives.5
Contraindications (such as use during pregnancy or breast-feeding) are the same for extended- and immediate-release carbamazepine.
TOLERABILITY
Carbamazepine in any form can cause a range of common to rare side effects (Table 2), which have been reviewed elsewhere.4-6
Side effects of ERC-CBZ most commonly reported during the double-blind, placebo-controlled studies include dizziness, nausea, somnolence, headache, vomiting, dyspepsia, dry mouth, pruritus, and benign rash. Slower upward titration of single nighttime doses—instead of the twice-daily dosing used in these studies—could prevent most of these effects.
Only one patient in either study developed a serious side effect possibly related to ERC-CBZ (fever with rash); the rash resolved 6 days after the drug was stopped.