Topamax (topiramate) is a medication that can be used to treat seizures in Dravet syndrome, a condition also known as severe myoclonic epilepsy in infancy. It is manufactured by Janssen Pharmaceuticals.
How Topamax works
Information is relayed through the brain by means of electrical signals traveling from one neuron to another. These electrical signals are generated and maintained by chemical messengers or neurotransmitters and different channels that allow the movement of molecules such as potassium and sodium in and out of nerve cells.
Seizures happen when neurons start firing at a much higher rate than normal. This so-called hyperexcitability is thought to be caused by alterations in the channels or chemical messengers controlling the electrical activity of nerve cells.
Most people with Dravet syndrome have a genetic defect in the SCN1A gene that causes the complete loss of function of a sodium channel called Nav1.1. This leads to frequent and prolonged seizures that may occur several times a day.
Topamax is an anticonvulsant that aims to prevent seizures from occurring. However, it is not well understood how it achieves this effect. It is thought it may work by increasing the activity of a neurotransmitter called GABA, which normally works to inhibit neuronal activity.
Topamax is often the first type of anticonvulsant medication used to treat Dravet syndrome, but it cannot be used to stop a seizure after it has already started.
Studies on Topamax
A study by the Second University of Naples, Italy, involved 18 participants with Dravet syndrome, ages two to 21, who were given a maximum dose of 12 mg per kilogram (kg) of daily Topamax in addition to one or two other anticonvulsants. After an average of one year of treatment, slightly more than half of the patients experienced decreases in the number of seizures they experienced with three patients having no seizures at all. None of the patients had worsening seizures. Four patients experienced side effects of slurred speech, nervousness, kidney stones, weight loss, and increased blood loss during menstruation.
A similar study looked at the effectiveness of Topamax as an add-on therapy to other anticonvulsants in 18 patients with Dravet syndrome, ages two to 22. After receiving a maximum dose of 6-8 mg per kg of daily Topamax for an average of 10.5, more than half of the patients had reduced number of seizures by 50 percent. Six patients had reduced number of seizures by more than 75 percent, and three patients became seizure-free. Side effects such as drowsiness and weight loss were mild and transient, lasting about 10 to 14 days, although weight loss persisted for longer. The research was conducted at the Hospital Infantil Universitario Virgen del Rocio in Spain.
Another study found Topamax to be effective in 36 children with Dravet syndrome whose seizures could not be adequately controlled with Diacomit (stiripentol), another anticonvulsant. Seizure frequency was reduced by 50 percent in more than half of the participants after an average of 13 months of Topamax at doses ranging from 0.6 – 9.2 mg per kg daily. Nearly 20 percent of patients were seizure-free for at least four months. The most frequent side effects experienced by patients were behavioral disturbances and gastrointestinal problems. Topamax had to be stopped in 17 percent of the patients, as it was either not well-tolerated or was not effective. This study was performed by researchers at the Hospital Necker-Enfants Malades in France.
Common side effects of Topamax include weight and appetite loss, mood changes such as anxiety and depression, memory and concentration impairments, confusion, poor coordination (ataxia), vision problems, nausea, dizziness, drowsiness, numbness, fatigue, taste alterations, and difficulty swallowing.
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