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.[1][2][3][4][5][6][7][8]

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.[9][10][11][6][12][13]

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.

A slow titration schedule of 25 to 50 mg/day weekly increments is preferred to decrease the frequency of adverse effects.[14][15]

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). 

The most common adverse effects in trials involving migraine patients were paresthesia and dysgeusia.[14][16][17][18]

More dangerous side effects include:

• Acute myopia and secondary angle-closure glaucoma[19]
• Oligohidrosis and hyperthermia: uncommon and reversible with cessation of the drug.[20]
• Metabolic acidosis: due to inhibition of carbonic anhydrase isoenzymes, TPM can lead to metabolic acidosis secondary to type II renal tubular acidosis, elevated urine pH, reduced urine citrate, hypercalciuria, calcium phosphate stone formation, bone mineralization defects.[21]
• Suicidal behavior and ideation[22]
• Cognitive/neuropsychiatric adverse reactions: influence of TPM on the hippocampus-related memory processes influence spacial memory, but does not significantly affect the learning process.[23]
• Fetal toxicity: Exposure during pregnancy associated with congenital malformations and developmental delay. Increased risk of recurrent malformations in future pregnancies.[24]
• Hyperammonemia and encephalopathy: one case report describes a young patient developing metabolic encephalopathy with hypoxic respiratory failure, most likely due to concurrent use of valproic acid and topiramate. Clinicians should be cautious of possible hyperammonemia encephalopathy in any patient who is taking these medications presenting with impaired consciousness and cognitive decline.[4]
• Kidney stones: long term TPM administration could induce urolithiasis; therefore, blood testing for acid-base balance, urinary pH, and citrates is recommended in patients suffering from kidney stones.[25]
• Paresthesia: is the most common cause for discontinuation of the drug.[26]
• Adjustment of dose in renal failure: dose adjustment is necessary for patients with moderate-to-severe renal impairment.[27]
• Decreased hepatic function: closer follow up, and more frequent monitoring of serum concentration is necessary to optimize clinical outcomes.[28]

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.[29]