Women with Epilepsy: A Handbook of Health and Treatment Issues (Chapter Seven)

Antiepileptic drugs and other treatments for epilepsy (Excerpt)

Jacqueline A. French

Drug effects specific to women

There has never been a proven difference in AED effects between men and women, although dosages may differ due to differences in body weight. Side effects are also similar in both sexes, but there are certain side effects that may be more troublesome to one sex than to the other. One of these is weight change. Some antiepileptic medications may cause weight gain. This side effect is always idiosyncratic and usually occurs in about one-third of patients. The most profound weight gain is seen in patients taking valproate, who may gain up to 30 lbs (13.6 kg). Other drugs, such as carbamazepine and gabapentin, also cause weight gain, but rarely more than 15 lb (6.8 kg). Other drugs, notably felbamate and topiramate, can cause weight loss. The cause of the weight change is unknown, but it is most likely to be due to alterations in basal metabolism. Diet and exercise can help, and the weight usually returns to baseline if the drug is discontinued. Phenytoin, in particular, can cause some cosmetic side effects that are troublesome to women. These include excessive hair growth, including on the face, and coarsening of facial features. These effects do not occur in everyone and are usually the result of long-term use. Because of these effects, many doctors do not prescribe phenytoin to young women.

Some AEDs, including phenytoin, carbamazepine, tiagabine, topiramate, Phenobarbital, and mysoline, are metabolized through the liver and speed up the elimination of other substances that are metabolized in the liver. Such drugs are called hepatic enzyme inducers. Some hormones critical to sexual function are metabolized in the liver and levels of these hormonal substances may be reduced by the AEDs listed above. The degree to which this affects human sexual function is controversial. It is also possible that AEDs may affect the pituitary gland directly. Because the pituitary gland regulates hormones, this may also affect sexual function. Patients who take AEDs may notice a reduction in sexual desire or a change in their menstrual cycles.

Oral contraceptives (birth control pills) are also metabolized through the liver and are affected by the presence of enzyme-inducing AEDs. The introduction of such a drug might cause breakthrough bleeding or reduce the contraceptive pill’s effectiveness. Therefore, all women taking an enzyme-inducing AED should be on a form of oral contraceptive that contains a higher dose of estrogen (50µg) or use a barrier method to prevent pregnancy.

Vitamin D, which is also metabolized through the liver, is essential to the body’s ability to absorb calcium and build healthy bones. Some patients taking hepatic enzyme-inducing antiepileptic medication have low calcium levels, or osteomalacia. Although osteoporosis has not been definitively linked to long-term AED therapy, it is reasonable for women with epilepsy to take calcium supplements and to discuss with their doctors the need for vitamin D supplementation.

-- Excerpted from "Women with Epilepsy: A Handbook for Health and Treatment Issues" edited by Martha J. Morrell, MD and Kerry L. Flynn, M.A. Published by Cambridge University Press, 2003. It is available for purchase in our marketplace.