TOPAMAX: Multiple Methods of Action

In vitro studies indicate that topiramate does not inhibit enzyme activity for CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2D6, CYP2E1, and CYP3A4/5 isozymes. In vitro studies indicate that topiramate is a mild inhibitor of CYP2C19 and a mild inducer of CYP3A4.⁶

Antiepileptic Drugs

Potential interactions between topiramate and standard AEDs were assessed in controlled clinical pharmacokinetic studies in patients with epilepsy. The effects of these interactions on mean plasma AUCs are summarized in Table 1.

The most clinically significant interactions may be pharmacodynamic rather than pharmacokinetic in nature because TOPAMAX is not highly protein bound or extensively metabolized in the liver and therefore has limited potential for pharmacokinetic interactions.

Clinically significant pharmacokinetic interactions with AEDs are limited to the effects of enzyme-inducing AEDs on TOPAMAX.

TOPAMAX [Prescribing Information]. Titusville, NJ: Ortho-McNeil Neurologics^®; 2006.
French JA, Kanner AM, Bautista J, et al. Efficacy and tolerability of the new antiepileptic drugs I: Treatment of new onset epilepsy patients. Report of the Therapeutics and Technology Assessment Subcommittee and Quality Standards Subcommittee of the American Academy of Neurology and the American Epilepsy Society. Neurology. 2004;62:1252-1260.
Bourgeois BFD. Pharmacokinetics and pharmacodynamics of antiepileptic drugs. In: Wyllie E, ed. The Treatment of Epilepsy: Principles and Practice. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2006:655-664.
Kyllonen KC, Gupta A. Selected drug interactions between antiepileptic drugs and other types of medications. In: Wyllie E, ed. The Treatment of Epilepsy: Principles and Practice. 4th ed. Philadelphia: Lippincott Williams & Wilkins;2006:665-669.
Nallani SC, Glauser TA, Hariparsad N, et al. Dose-dependent induction of cytochrome P450 (CYP) 3A4 and activation of pregnane X receptor by topiramate. Epilepsia. 2003;44:1521-1528.
Data on file, Ortho-McNeil Neurologics^®
Baram TZ, Hartman AL, Vining EPG, et al. Seizures. In: Johnson RT, Griffin JW, McArthur JC, eds. Current Therapy in Neurologic Disease. 7th ed. Philadelphia: Mosby;2006:23-53.
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Physician's Desk Reference Web site. Available at: www.pdr.net. Accessed February 5, 2007.
Arroyo S, Dodson WE, Privitera MD, et al, for the EPMN-106/INT-28 Investigators. Randomized dose-controlled study of topiramate as first-line therapy in epilepsy. Acta Neurol Scand. 2005;112:214-222.
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Elterman RD, Glauser TA, Wyllie E, et al, and the Topirmate YP Study Group. A double-blind, randomized trial of topiramate as adjunctive therapy for partial-onset seizures in children. Neurology. 1999;52:1338-1344.
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Important

Avoid confusion with Toprol-XL^® (metoprolol succinate) by spelling out TOPAMAX^® (topiramate) on your prescription. Toprol-XL is a registered trademark of the AstraZeneca group of companies.

About TOPAMAX

TOPAMAX is indicated as initial monotherapy in patients 10 years of age and older with partial-onset or primary generalized tonic-clonic seizures.

Effectiveness was demonstrated in a controlled trial in patients with epilepsy who had no more than 2 seizures in the 3 months prior to enrollment. Safety and effectiveness in patients who were converted to monotherapy from a previous regimen of other anticonvulsant drugs have not been established in controlled trials.

TOPAMAX is indicated as adjunctive therapy in patients 2 years of age and older with primary generalized tonic-clonic seizures, partial-onset seizures, or seizures associated with Lennox-Gastaut syndrome.

IMPORTANT SAFETY INFORMATION

TOPAMAX has been associated with serious adverse events including: hyperchloremic, non-anion gap metabolic acidosis (lowering of serum bicarbonate levels)—measurement of baseline and periodic serum bicarbonate levels is recommended; acute myopia and secondary angle-closure glaucoma—patients should seek medical attention if they experience blurred vision or ocular pain; oligohidrosis and hyperthermia—occurs most often in hot weather and in children; cognitive/psychiatric side effects including somnolence, fatigue, cognitive dysfunction, and psychiatric/behavioral disturbances including suicidal thoughts or behavior; hyperammonemia with or without encephalopathy—associated with the concomitant use of valproic acid; and kidney stones—patients should maintain an adequate fluid intake to minimize the risk of renal stone formation.

As monotherapy, the most common side effects of TOPAMAX (in the 400 mg/day group and at a rate higher than the 50 mg/day group) in adults were: paresthesia, weight decrease, somnolence, anorexia,* dizziness, and difficulty with memory; and in children: weight decrease, upper respiratory tract infection, paresthesia, anorexia, diarrhea, and mood problems.

In combination with other antiepileptic drugs (AEDs), the most common side effects of TOPAMAX in adults (200 to 400 mg/day) were: somnolence, dizziness, nervousness, ataxia, fatigue, speech disorders and related problems, psychomotor slowing, abnormal vision, difficulty with memory, paresthesia, and diplopia; and in children (5 to 9 mg/kg/day): fatigue, somnolence, anorexia, nervousness, difficulty with concentration/attention, difficulty with memory, aggressive reaction, and weight decrease.

In women taking combination oral contraceptives with TOPAMAX, a significant decrease in estrogen exposure has been shown at TOPAMAX doses ≥ 200 mg/day. The possibility of decreased contraceptive efficacy and increased breakthrough bleeding should be considered.

*Anorexia is defined as loss of appetite.

Please see full US Prescribing Information.

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