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Objective: To investigate potential drug-drug interactions between topiramate and metformin and pioglitazone at steady state., Methods: Two open-label studies were performed in healthy adult men and women. In Study 1, eligible participants were given metformin alone for 3 days (500 mg twice daily [BID]) followed by concomitant metformin and topiramate (titrated to 100mg BID) from days 4 to 10. In Study 2, eligible participants were randomly assigned to treatment with pioglitazone 30 mg once daily (QD) alone for 8 days followed by concomitant pioglitazone and topiramate (titrated to 96 mg BID) from days 9 to 22 (Group 1) or to topiramate (titrated to 96 mg BID) alone for 11 days followed by concomitant pioglitazone 30 mg QD and topiramate 96 mg BID from days 12 to 22 (Group 2). An analysis of variance was used to evaluate differences in pharmacokinetics with and without concomitant treatment; 90% confidence intervals (CI) for the ratio of the geometric least squares mean (LSM) estimates for maximum plasma concentration (Cmax), area under concentration-time curve for dosing interval (AUC12 or AUC24), and oral clearance (CL/F) with and without concomitant treatment were used to assess a drug interaction., Results: A comparison to historical data suggested a modest increase in topiramate oral clearance when given concomitantly with metformin. Coadministration with topiramate reduced metformin oral clearance at steady state, resulting in a modest increase in systemic metformin exposure. Geometric LSM ratios and 90% CI for metformin CL/F and AUC12 were 80% (75%, 85%) and 125% (117%, 134%), respectively. Pioglitazone had no effect on topiramate pharmacokinetics at steady state. Concomitant topiramate resulted in decreased systemic exposure to pioglitazone and its active metabolites, with geometric LSM ratios and 90% CI for AUC24 of 85.0% (75.7%, 95.6%) for pioglitazone, 40.5% (36.8%, 44.6%) for M-III, and 83.8% (76.1%, 91.2%) for M-IV, respectively. This effect appeared more pronounced in women than in men. Coadministration of topiramate with metformin or pioglitazone was generally well tolerated by healthy participants in these studies., Conclusions: A modest increase in metformin exposure and decrease in topiramate exposure was observed at steady state following coadministration of metformin 500 mg BID and topiramate 100mg BID. The clinical significance of the observed interaction is unclear but is not likely to require a dose adjustment of either agent. Pioglitazone 30 mg QD did not affect the pharmacokinetics of topiramate at steady state, while coadministration of topiramate 96 mg BID with pioglitazone decreased steady-state systemic exposure to pioglitazone, M-III, and M-IV. While the clinical consequence of this interaction is unknown, careful attention should be given to the routine monitoring for adequate glycemic control of patients receiving this concomitant therapy. Concomitant administration of topiramate with metformin or pioglitazone was generally well tolerated and no new safety concerns were observed., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Purpose: Topiramate is primarily renally excreted. Chronic renal and hepatic impairment can affect the clearance of topiramate. Therefore, the objective was to establish dosage guidelines for topiramate in chronic renal impairment, end-stage renal disease (ESRD) undergoing hemodialysis, or chronic hepatic impairment patients., Methods: In 3 separate open-label, parallel group studies (n=5-7/group), in patients with mild-moderate and severe renal impairment (based on creatinine clearance), ESRD requiring hemodialysis, or moderate-severe hepatic impairment (based on Child-Pugh classification) and matching healthy participants, pharmacokinetics of a single oral 100mg topiramate was determined., Results: Compared with healthy controls, overall exposure (AUC0-∞) for topiramate was higher in mild-moderate (85%) and severe renal impairment (117%), consistent with significantly (p<0.05) lower apparent total body clearance (CL/F) and renal clearance (CLR), leading to longer elimination half-life. Both CLR and CL/F of topiramate correlated well with renal function. CL/F was comparable in ESRD and severe renal impairment. Half of usual starting and maintenance dose is recommended in moderate-severe renal impairment patients, and those with ESRD. Hemodialysis effectively removed plasma topiramate with mean dialysis clearance approximately 12-fold greater than CL/F (123.5 mL/min versus 10.8 mL/min). Compared with healthy matched, patients with moderate-severe hepatic impairment exhibited small increase (29%) in topiramate peak plasma concentrations and AUC0-∞ values, consistent with lower CL/F (26%). Topiramate was generally well tolerated., Conclusion: Half of usual dose is recommended for moderate-severe renal impairment and ESRD. Supplemental dose may be required during hemodialysis. Dose adjustments might not be required in moderate-severe hepatic impairments; however, the small sample size limits generalization., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Purpose: To characterize the pharmacokinetics of adjunctive topiramate in infants (1-24 months) with refractory partial-onset seizures (POS); also to evaluate safety and tolerability of topiramate in the dose range of 3-25 mg/kg/day., Methods: In this open-label phase 1 study, infants (N = 55) with refractory POS receiving at least one concurrent antiepileptic drug (AED) were enrolled. Infants were stratified by age and randomly assigned to one of four topiramate target dose groups (3-, 5-, 15-, or 25 mg/kg/day). Treatment was initiated at 3 mg/kg/day with titration to the target dose by weekly dose escalation. Topiramate was administered daily in two divided doses as oral liquid (5 mg/ml for infants <9 kg or those who could not tolerate solid foods) or sprinkle capsule (25 mg) formulations. Following seven consecutive days of topiramate administration at the target dose, four blood samples were collected from each infant for pharmacokinetic assessments (predose, 1-3, 4-6, and 8-10 h postdose)., Key Findings: Fifty-five infants (mean [SD] age in months: 11.4 [5.79]) with POS were enrolled, of whom 33% had seizures with or without secondary generalization. Complete pharmacokinetic profiles were obtained in 35 infants in whom mean plasma topiramate concentration-time profiles demonstrated linear pharmacokinetics (predose topiramate concentrations [C(trough) ] and area under the plasma concentration-time curve from time 0 through 12 h [AUC(12 h)]) of topiramate over the dose range studied). Apparent steady state oral clearance (CL(ss) /F) remained similar across all topiramate target dose groups and was independent of creatinine clearance, age, and weight. Mean values for CL(ss) /F were approximately twofold greater in infants receiving concomitant enzyme-inducing AEDs versus enzyme-inhibiting AEDs. Topiramate was well tolerated and safety findings were consistent with previous reports in children and adults. Most common treatment emergent adverse events (≥10%) were upper respiratory tract infection, fever, vomiting, somnolence, and anorexia., Significance: In infants (1-24 months), topiramate exhibited linear steady state pharmacokinetics over the dose range 3-25 mg/kg/day, and CL(ss) /F of topiramate was independent of dose. Moreover, the concomitant enzyme-inducing AEDs doubled the clearance of topiramate. Topiramate was generally well tolerated as adjunctive therapy at doses up to 25 mg/kg/day., (Wiley Periodicals, Inc. © 2012 International League Against Epilepsy.)

Data from 2 studies (phase 1 and phase 3) in infants <2 years old (N = 284; mean [SD] age, 12[6.3] months) with refractory partial-onset seizures were pooled to assess the long-term safety up to 1 year (primary objective) and tolerability of adjunctive topiramate treatment (mean treatment duration = 282 days). Monthly seizure rate summaries were also assessed. During the open-label extensions of these studies, study medication was first titrated to a dose of 25 mg/kg/d with subsequent uptitration to the maximum dosage tolerated, or seizure freedom, or a maximum of 60 mg/kg/d, whichever occurred first. The most common treatment-emergent adverse events (≥30%) were fever (52%), respiratory tract infections (51%), anorexia (35%), and acidosis (31%). Mean (SD) changes from pretreatment baseline to endpoint in Z scores for growth parameters were as follows: -0.82 (1.19) (body weight), -0.45 (1.60) (body length), and -0.36 (1.02) (head circumference).Tolerability in infants was consistent with previous studies.