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Daily doses from 600 to 2,400 mg/day have been shown to be safe and effective for adults with normal renal function, although most patients are not able to tolerate the 2,400 mg/day dose without reduction of other antiepileptics, mainly because of additive CNS-related adverse events, such as sedation.
These doses are typically given in a twice-a-day regimen. If the total is 1500mg per day, it would normally be divided.
Daily doses above 2,400 mg/day have not been studied systematically in clinical trials.
For children 4-16 (or very small adults), the proper dose depends on weight. Doses up to a maximum dose of 46 mg/kg/day, to achieve the desired clinical response, are used.