Carbamazepine

Definition

Carbamazepine (Tegretol, Carbatrol) may be administered to cancer patients as a pain medicine.

Purpose

Carbamazepine is given to cancer patients primarily as a pain medication. The drug may, for example, be prescribed for stabbing pain that moves along a nerve. For noncancer patients, it is often used to treat epilepsy or bioplar disorder (manic-depressive illness).

Description

Carbamazepine suppresses some of the activities of the nerves. It does this by delaying the amount of time it takes for certain passageways in the nerves to recover after they have sent out a message.

Recommended dosage

Carbamazepine comes in several forms. There are 200 mg tablets, 100 mg chewable tablets, and a liquid containing 20 mg per milliliter that may be swallowed. There are extended-release tablets of carbamazepine containing 100, 200, or 400 mg and extended release capsules of the medication containing 200 and 300 mg.

Some authorities recommend starting with 100 to 200 mg twice a day. This strategy helps to minimize side effects. Then, the dose may be gradually increased every week. Adults may eventually receive 600 to 1200 mg a day, while 20 to 30 mg per kg of body weight per day is appropriate for children.

Side effects

Carbamazepine may exhibit side effects to the nervous system, for example, drowsiness, dizziness, blurred vision, unsteadiness, depression, impaired concentration, and headache. Patients should be cautious about operating machinery or performing tasks requiring alertness until tolerant of the side effects. After several weeks of treatment, these side effects may disappear. To minimize these side effects, doctors may start carbamazepine at a low dose and may recommend that it be taken before bedtime. As carbamazepine may cause stomach upset and nausea, the medicine should be taken with meals.

Effects of carbamazepine may include bone marrow suppression, which involves a low white blood cell and platelet count, but this is usually not severe. Very rarely, a dangerous anemia may occur during carbamazepine therapy. Blood counts should be monitored for patients using this drug. Some patients with previously diagnosed depression of the bone marrow should not be given carbamazepine.

Carbamazepine may cause birth defects and should be avoided in women who are pregnant. An appropriate contraceptive method should be used while on carbamazepine. Carbamazepine can cross into breast milk and should be avoided in women who are breastfeeding. Carbamazepine may also cause rash or sensitivity to the sun.

Interactions

Carbamazepine may affect the activity of other medicines, for example, oral contraceptives, warfarin, theophylline, doxycycline, haloperidol, corticosteroids, valproate, clonazepam, ethosuximide, lamotrigine, felbamate, and thyroid hormones. Oral contraceptives may become less effective if a patient is taking carbamazepine. Some doctors recommend that the form of birth control pill be altered or that a different method of contraception be used. If phenytoin and phenobarbital are taken at the same time as carbamazepine, the capacity of carbamazepine to interact with additional medications may increase. Side effects may occur if a patient is taking carbamazepine and one of the following medications simultaneously: danazol, dextropropoxyphene, erythromycin, clarithromycin, isoniazid, verapamil, or diltiazem. Due to the numerous potential of interactions with other drugs, patients should consult with their physician or pharmacist prior to starting any new medications either bought over the counter or initiated by another physician. Patients taking carbamazepine should not drink grapefruit juice.

Bob Kirsch

Bone marrow

—The spongy tissue found in the large bones of the body.

Trigeminal neuralgia

—A nerve problem associated with pain.