<p>The addition of topiramate to other antiepileptic drugs (phenytoin, carbamazepine, valproic add, phenobarbitai, primidone) has no clinically significant effect on their steady-state plasma concentrations, except in some patients where the addition of topiramate to phenytoin may result in an increase of plasma concentrations of phenytoin.<br />
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<strong>CNS Depressants</strong>: Topiramate should be used with caution if used in combination with alcohol and other CNS depressants.<br />
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<strong>Oral Contraceptives</strong>: In an interaction study with a combined oral contraceptive, Topiramate increased plasma clearance of the oestrogenic component significantly. Consequently, and bearing in mind the potential risk of teratogenicity, patients should receive a preparation containing not less than 50 &mu;g of oestrogen or use some alternative non-hormonal method of contraception. Patients taking oral contraceptives should be asked to report any change in their bleeding patterns.<br />
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<strong>Lithium</strong>: In patients with bipolar disorder, the pharmacokinetics of lithium were unaffected during treatment with Topiramate at doses of 200 mg/day; however, there was an observed increase in systemic exposure (26% for AUC) following Topiramate doses of up to 600 mg/day. Lithium levels should be monitored when co-administered with Topiramate.<br />
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<strong>Hydrochlorothiazide</strong>&nbsp;(HCTZ): The steady-state pharmacokinetics of HCTZ were not significantly influenced by the concomitant administration of Topiramate. Clinical laboratory results indicated decreases in serum potassium after Topiramate or HCTZ administration, which were greater when HCTZ and Topiramate were administered in combination.<br />
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<strong>Metformin</strong>: Topiramate did not affect metformin tmax. The clinical significance of the effect of topiramate on metformin pharmacokinetics is unclear. Oral plasma clearance of topiramate appears to be reduced when administered with metformin. The clinical significance of the effect of metformin on topiramate pharmacokinetics is unclear. When Topiramate is added or withdrawn in patients on metformin therapy, careful attention should be given to the routine monitoring for adequate control of their diabetic disease state.<br />
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<strong>Pioglitazone</strong>: When Topiramate is added to pioglitazone therapy or pioglitazone is added to Topiramate therapy, careful attention should be given to the routine monitoring of patients for adequate control of their diabetic disease state.<br />
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<strong>Glibenclamide</strong>: The steady-state pharmacokinetics of Topiramate were unaffected by concomitant administration of glibenclamide. When Topiramate is added to glibenclamide therapy or glibenclamide is added to Topiramate therapy, careful attention should be given to the routine monitoring of patients for adequate control of their diabetic disease state.<br />
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<strong>Others</strong>: Topiramate, when used concomitantly with other agents predisposing to nephrolithiasis, may increase the risk of nephrolithiasis. While using Topiramate, agents like these should be avoided since they may create a physiological environment that increases the risk of renal stone formation. The interaction with benzodiazepines has not been studied.&nbsp;<br />
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<strong>Valproic Acid</strong>: Concomitant administration of Topiramate and valproic acid has been associated with hyperammonemia with or without encephalopathy in patients who have tolerated either drug alone. An association of hyperammonemia with Topiramate monotherapy or concomitant treatment with other anti epileptics has not been established.</p>