In general, patients taking Felbatol (felbamate) may have a significantly greater risk of developing aplastic anemia (a frequently fatal disorder) than the population as a whole, but there is no reliable way of determining the absolute risk for any individual. This risk has been controversial since the first reports of fatalities in people taking Felbatol surfaced soon after the medication was introduced.

Today, the long-term outlook for patients with aplastic anemia is variable. Many patients are apparently cured, but others suffer relapses that require transfusions and further treatments. Some who survive for years ultimately develop serious complications that may prove fatal.

The hottest topic associated with Felbatol currently is whether an enzyme test (performed on blood or urine) can reliably identify the very small number of patients taking Felbatol who are in the greatest danger from this rare problem. Finding such a test would let doctors prescribe Felbatol with much less worry.

To help you understand the risk of experiencing toxic side effects with felbamate, the chronology below covers this subject from felbamate's appearance on the market to recent, cutting-edge research.

1993: Felbatol is approved by the United States Food and Drug Administration (FDA). The outlook on its efficacy is favorable, as reported in a study at the Department of Neurosciences, Wright-Patterson AFB in Ohio. This report said that felbamate has a "broad range of efficacy as well as a favorable safety profile," but it also noted that "its role in clinical practice awaits further investigation of recently reported cases of aplastic anemia." (Burdette & Sackellares 1994).

1997: The reports of aplastic anemia surface from patients taking felbamate. An evaluation of the first 31 reports of cases of aplastic anemia (from about 110,000 patients who had taken Felbatol) determined that the incidence of the disease in patients taking Felbatol was somewhere between 27 and 209 per million (probably about 127 per million), versus about 2 per million in the general population. These researchers concluded that there is an association between Felbatol use and aplastic anemia, but factors like the use of other medications make it difficult to assign a precise risk. (Kaufman et al. 1997)

1998: After warnings against Felbatol use, many doctors advised their patients to stop taking it. A study at the University of Cincinnati Medical Center evaluated the seizure frequency after Felbatol was discontinued. Forty-five adult patients who had received Felbatol for at least one month were instructed to taper off of the Felbatol over two weeks, while continuing to take other seizure medicines. Patients kept a diary of their seizures during the month of tapering off and 3 months afterwards. The result? Patients experienced a significant increase in seizure frequency (compared to the 6 months before they started taking Felbatol) during and after withdrawal from Felbatol. (Welty et al., 1998)

1999: A specific metabolite known as atropaldehyde, proposed to play a role in the development of serious adverse effects like aplastic anemia, is identified in patients taking Felbatol. Scientists at the University of Virginia speculated that the amount of atropaldehyde formed in an individual patient would be correlated with the potential for developing the disease. They studied a method for measuring the amount of related substances in the urine of 31 patients taking Felbatol and found it to be precise enough to allow monitoring of patients for high levels and the resulting higher risk. (Thompson et al, 1999)

An article reviewing the status of felbamate for doctors noted that the idea of identifying high-risk patients is a promising one, which should allow better use of Felbatol, a medication that is effective in controlling seizures for patients with many types of epilepsy. (Pellock 1999)

2001: Research continued to work on ways to alter the reactions that lead to harm from substances like atropaldehyde in patients taking Felbatol. (Dieckhaus et al., 2001)