Allergic side effects

As with other anticonvulsants, a drug rash occurring within the first two to three weeks after starting carbamazepine is a potentially serious sign. A child with a rash beginning at this time should always be seen promptly by your physician, who can then decide whether to discontinue the drug. Rare effects on the liver, bone marrow, and blood clotting cells (platelets) have also been reported.

Dose-related side effects

The signs of dose-related toxicity from carbamazepine are important because they are briefly experienced by almost everyone who uses it. The first sign of mild toxicity is double vision, sometimes accompanied by blurred vision or dizziness, most likely to occur one to two hours after a dose, when the amount of the drug in the blood is at its highest. Such symptoms last one to two hours, until the blood level decreases, not a serious side effect. If persistent and bothersome, your physician may want either to lower the dose or to spread out the medicine in more frequent, smaller doses.

More significant toxicity is displayed in unsteadiness, ataxia, sleepiness, or foggy thinking. These symptoms should be brought to the attention of your physician, who will want to check the blood level of the drug and perhaps change your child’s dose. All of these symptoms disappear when the dosage is decreased or the drug is discontinued.

Because of carbamazepine’s short half-life, physicians often recommend that it be taken three or even four times each day. We, and most patients, find that taking a drug this often is cumbersome, and that patients often forget to take some doses. We prescribe the drug to be taken only twice a day. We tell the patient (or the parent) to observe carefully if seizures occur before the next dose. If they do, then we assume that the blood level dropped too low or that the time between doses is too long and change the schedule to three or, infrequently, four times a day.

The other reason why we may decide to give the drug more often than twice a day is a patient’s experience of signs or symptoms of toxicity shortly after taking a dose. This indicates that we have given too much at one time, and again we will instruct the patient to take a smaller dose of the drug three times a day. Using this approach, we have found that the seizures of most children can be controlled if they take carbamazepine only twice a day.

In children taking carbamazepine who are given erythromycin (an antibiotic often used in place of penicillin) for infection, high levels of carbamazepine and toxicity often develop. If your physician prescribes erythromycin, he may need to lower the dose of carbamazepine temporarily.

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