Tegretol®, Carbatrol® (Carbamazepine)
One of the oldest and still most widely used anti-epileptic drugs (AEDs) is carbamazepine. Carbamazepine works for epilepsy by blocking voltage-sensitive sodium (Na+) channels. It is usually thought of as a partial onset seizure medication although it does have activity in treating some generalized seizure disorders. It comes in many forms including liquid suspension, chewable tablets, and tablets known as Tegretol®. It also comes in two extended release forms Tegretol-XR® and Carbatrol®.
The Tegretol-XR® form works on the principal of a tablet which does not dissolve but rather allows water to enter through tiny pores and force out the medication. This slows the absorption of the medication and allows for twice a day dosing.
The Carbatrol® works by using a series of three different beads that dissolve at different rates and therefore spread out absorption and again allows twice daily dosing. In the Carbatrol® method, the capsules can be opened and the beads can be taken over food or with a spoon for those who cannot swallow.
The Carbatrol® tablets come in 200 mg and 300 mg sizes and the Tegretol-XR tablet comes in 100 mg, 200 mg, and 400 mg sizes and therefore the final dosing may commonly affect the choice of tablet type.
Carbamazepine does cause birth defects and all women of childbearing age should take extra folic acid to help minimize the risk of neural tube defects. The patient discussing her plans for pregnancy before trying to become pregnant minimizes risk to the fetus. The medication also lowers the effectiveness of birth control pills by increasing the metabolism of the estrogen component and therefore it is recommend to not use the lowest dose estrogen compounds available. Women who particularly do not want to get pregnant should consider using a barrier method in addition to their birth control pill.
Carbamazepine’s potential serious side effects include liver toxicity and decreased white blood cell counts (neutropenia). Patients who get a fever while taking this medication may need to be seen emergently. More common side effects that limit its ultimate dose include double vision, blurred vision, nausea, vomiting, or being off balance. There are a number of potential drug interactions with this medication. Most commonly, when some patients receive an erythromycin type antibiotic they may become toxic on this medication. Carbamazepine has also been associated with bone mineral loss by some studies although not as severe as that seen with Dilantin®. Somewhat more troubling is some epidemiologic data suggesting that Carbamazepine may increase the risk of SUDEP (Sudden Unexpected Death in Epilepsy).
Carbamazepine is also widely used to treat neuropathic pain of all types. This includes neuropathic pain on the face (trigeminal neuralgia), diabetes (diabetic neuralgia), and the shingles (post-herpetic neuralgia). As with all pain syndromes, the key is to increase the dose slowly until the pain is relieved or until the patient experiences some toxicity.Trileptal® or oxcarbazepine is felt to be very similar in its mode of action to carbamazepine but has very different side effects. It many instances, it is being used in place of carbamazepine with a relatively easy conversion between the two.
Carbatrol® or Tegretol® is widely used by psychiatrists as a mood stabilizing medication as well.