Maximum Daily Dose of Lithium
The maximum recommended daily dose of lithium carbonate is 1800 mg per day (600 mg three times daily), though the FDA-approved labeling does not specify an absolute ceiling dose—rather, dosing is guided by achieving therapeutic serum levels of 1.0-1.5 mEq/L for acute mania and 0.6-1.2 mEq/L for maintenance therapy. 1
FDA-Approved Dosing Parameters
- For acute mania: The typical effective dose is 600 mg three times daily (1800 mg/day total), which normally produces serum lithium levels between 1.0-1.5 mEq/L 1
- For long-term maintenance: Doses of 300 mg three to four times daily (900-1200 mg/day total) typically maintain therapeutic levels of 0.6-1.2 mEq/L 1
- Dosing must be individualized based on serum levels drawn 8-12 hours after the last dose, not on a fixed maximum milligram amount 1
Age-Related Maximum Doses
The usual maintenance daily doses vary significantly by age:
- Patients under 40 years: 25-35 mmol/day (925-1300 mg lithium carbonate) 2
- Patients 40-60 years: 20-25 mmol/day (740-925 mg) 2
- Patients over 60 years: 15-20 mmol/day (550-740 mg) 2
- Elderly patients require lower starting doses (150 mg/day) due to increased sensitivity and reduced clearance 3
Critical Dosing Considerations
Serum levels, not milligram doses, determine toxicity risk. Patients abnormally sensitive to lithium may exhibit toxic signs at serum levels of 1.0-1.5 mEq/L, which are considered therapeutic for most patients 1. Elderly patients often show toxicity at levels ordinarily tolerated by younger individuals 1.
Renal Impairment Adjustments
- GFR < 60 mL/min/1.73 m²: Consider lower doses with more frequent monitoring 3
- GFR < 30 mL/min/1.73 m²: Reduce dose by 50% 3
- Significant renal impairment is considered a contraindication to lithium use 3
Monitoring Requirements
- During acute phase: Check serum levels twice weekly until stable 1
- During maintenance: Monitor serum levels at least every 2 months in uncomplicated cases 1
- Blood samples must be drawn 8-12 hours after the previous dose when concentrations are relatively stable 1
Common Pitfall
Total reliance on serum levels alone is inadequate—accurate patient evaluation requires both clinical assessment and laboratory analysis 1. Early signs of toxicity include tremor, nausea, diarrhea, and polyuria-polydipsia, which may occur even within "therapeutic" ranges in sensitive individuals 4.