Lamotrigine 100 mg Dosing Frequency
Lamotrigine 100 mg is typically taken once or twice daily, depending on the total daily dose and whether you are taking other medications that affect its metabolism. 1
Standard Dosing Schedules
Once-Daily Dosing
- Lamotrigine can be administered as a single daily dose when the total daily amount is 100-200 mg, particularly during maintenance therapy for bipolar disorder or epilepsy. 1
- Extended-release formulations are specifically designed for once-daily administration, improving adherence and maintaining stable drug levels throughout the day. 1
Twice-Daily Dosing
- Divided dosing (twice daily) is recommended when total daily doses exceed 200 mg or when patients experience peak-related side effects such as dizziness or diplopia with once-daily administration. 2, 3
- Patients taking enzyme-inducing antiepileptic drugs (phenytoin, carbamazepine, phenobarbital) typically require twice-daily dosing because these medications shorten lamotrigine's half-life to 13.5-15 hours, necessitating more frequent administration to maintain therapeutic levels. 1, 3
Key Factors Determining Dosing Frequency
Drug Interactions That Affect Frequency
- Valproic acid extends lamotrigine's half-life to 48-59 hours, allowing once-daily dosing even at higher total daily doses, though the total daily amount must be reduced by approximately 50% to prevent toxicity. 1, 3
- Enzyme-inducing AEDs accelerate lamotrigine clearance, requiring twice-daily administration to maintain adequate serum concentrations throughout the dosing interval. 1, 3
Clinical Context
- For bipolar disorder maintenance, the standard target dose is 200 mg/day, which can be given as a single daily dose after the titration period is complete. 1, 4
- For epilepsy, doses ranging from 100-400 mg/day are common, with higher doses typically split into twice-daily administration to minimize neurological side effects like diplopia and ataxia. 2, 5
Important Caveats
- Never split, crush, or chew extended-release tablets—these must be swallowed whole to maintain once-daily pharmacokinetics. 1
- Regular (immediate-release) tablets can be taken once or twice daily based on total dose and tolerability, but should be swallowed whole with water. 1
- If you miss a dose for more than 5 days, do not resume your previous maintenance dose—restart the full titration schedule beginning at 25 mg daily to prevent rapid accumulation and serious rash. 1
- Trough blood levels should be drawn 12-16 hours after the last dose for once-daily regimens, or immediately before the morning dose for twice-daily schedules, to accurately assess therapeutic concentrations. 1