Topiramate (TPM) is a compound that belongs to the family of medications called antiepileptic drugs (AEDs). AEDs are generally used for neurologic and psychiatric purposes. The primary indication for this family of drugs is for seizure disorders; hence then name "antiepileptic drugs." In psychiatry, these are classically used as mood stabilizers, although their administrations have seen a broader application. Specifically, topiramate is an anticonvulsant drug that was initially FDA approved in 1996 for the treatment of monotherapy epilepsy, adjunctive therapy epilepsy, and migraine disorder. It has received approval for monotherapy in epilepsy in those two years or older with primary generalized onset tonic-clonic seizures or partial-onset seizures. Adjunctive therapy is an approved use for adults and pediatric populations ages 2 to 16 years old with primary generalized onset tonic-clonic seizures, partial-onset seizures, and in those two years or older with Lennox-Gastaut syndrome associated seizures. For migraine disorder, TPM has approval for prophylaxis in adults (FDA, 2012). For individuals with a body mass index over 30, TPM has approval for chronic weight management.
There are many off-label uses for topiramate including neuropathic pain, psychotropic drug-induced weight gain, alcohol use disorders with tobacco dependence, cluster headache prevention, binge eating disorder, bulimia nervosa, obesity with hypertension, prevention of neuralgiform attacks, adjunctive therapy in bipolar disorder, unipolar depression, borderline personality disorder, obsessive-compulsive disorder, posttraumatic stress disorder, Tourette syndrome, Prader-Willie syndrome, essential tremor.
Although the precise mechanism of action of topiramate is unknown, there is sufficient evidence to explain the anticonvulsant activity of the drug. TPM blocks voltage-gated sodium channels, which most likely leads to control of sustained depolarizations during seizures. TPM reduces membrane depolarization by AMPA/Kainate receptors. TPM enhances GABA (A) receptor activity, which enhances inhibitory effects. TPM is a weak inhibitor of carbonic anhydrase; acidosis in the brain has partial protection against seizures by downregulating NMDA receptor activity. Overall, the effect of TPM on these channels is the leading explanation of the antiepileptic action of the drug.
For the adult and pediatric population, topiramate is available in two oral preparations, immediate-release (taken twice daily) and extended-release (taken once daily). Patients should not crush the tablets since there is a bitter taste. There is a sprinkle capsule formulation that the patient may add to a small amount of soft food; TPM administration may be without regard to meals. Alcohol should be avoided 6 hours before and after the administration of TPM.
Adverse effects are dose-dependent and therefore differ between epilepsy and migraine patients in trials as the trials used different doses based on the condition.
Most common adverse effects in epilepsy trials included the involvement of central nervous system (paresthesia, fatigue, cognitive problems, dizziness, somnolence, psychomotor slowing, memory/concentration difficulties, nervousness, confusion), endocrine/metabolism (weight loss, anorexia), respiratory (infection), miscellaneous (fever, flushing).
More dangerous side effects include:
Topiramate is a relatively safe drug, as the list of absolute contraindications is minimal. As a carbonic anhydrase inhibitor, TPM can precipitate the development of metabolic acidosis and is, therefore, contraindicated in individuals currently with (or prone to experiencing) metabolic acidosis. Other contraindications include those with a history of a proven allergy to TPM, or within six hours before and six hours after alcohol use.
Baseline, as well as periodic serum bicarbonate levels, are required monitoring protocol for individuals on topiramate due to concern for hyperchloremic metabolic acidosis.
Fortunately, there are no reports of fatalities with topiramate monotherapy. Symptoms of toxicity include sedation, speech disturbance, blurred vision, metabolic acidosis, agitation, ataxia, convulsions, and abdominal pain.
In seven cases of TPM toxicity observed by Polish Poison Control Centers, the most common symptom for TPM toxicity was somnolence (66.7%), along with agitation, mydriasis, and vertigo (33.4%). One individual experienced three tonic-clonic seizures. There were no fatalities or long term consequences observed.
A specific antidote is not currently available.
Topiramate, like many other pharmaceuticals, is only FDA approved for a few conditions. However, there are many off label uses for this drug. Off-label use means that a clinician prescribes the medication for an indication that was not studied and approved by the FDA. Physicians are not monitored as to how they prescribe topiramate; therefore, it is up to the clinician to choose when to use a medication off-label based on clinical judgment and experience while calculating the risks and benefits. Off-label use is more common in patient populations that are less likely to be included in clinical trials such as psychiatric, pregnant, and pediatric patients. Therefore, it is the responsibility of the healthcare professionals to continually educate themselves on the most up to date information regarding new medical information, especially regarding those medications used off-label, such as TPM. Moreover, because of the relatively few contraindications associated with TPM, healthcare teams should be less hesitant when considering the application of the off label use of TPM.
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