Lithium Dosing and Laboratory Monitoring
Initial Dosing Strategy
For acute mania, start with lithium carbonate 600 mg three times daily (1800 mg/day total) in most adults, targeting serum levels of 1.0-1.5 mEq/L, but reduce the starting dose to 150 mg/day in elderly patients due to their increased sensitivity and reduced clearance. 1, 2
Age-Specific Dosing Considerations
- Adults under 40 years: Typical maintenance dose is 925-1300 mg daily (25-35 mmol) 3
- Adults 40-60 years: Reduce to 740-925 mg daily (20-25 mmol) 3
- Adults over 60 years: Further reduce to 550-740 mg daily (15-20 mmol), as the dose required to achieve a given serum concentration decreases threefold from middle to old age 3, 4
- Elderly patients: Start at 150 mg/day as they often exhibit toxicity at levels ordinarily tolerated by younger patients 2, 1
Renal Impairment Adjustments
- GFR < 60 mL/min/1.73 m²: Use lower doses with more frequent monitoring 2
- GFR < 30 mL/min/1.73 m²: Reduce dose by 50% 2
- Significant renal impairment: Consider this a contraindication to lithium therapy 2
Baseline Laboratory Assessment
Before initiating lithium, obtain the following baseline tests: 2, 5
- Complete blood count 2, 5
- Thyroid function tests (TSH, free T4) 2, 5
- Renal function (BUN, creatinine, GFR) 2, 5
- Serum electrolytes including calcium 2, 5
- Urinalysis 2, 5
Therapeutic Serum Level Targets
Target serum lithium levels based on clinical indication:
- Acute mania: 1.0-1.5 mEq/L 1
- Long-term maintenance: 0.6-1.2 mEq/L 1
- Augmentation of antidepressants: Lower levels of 0.2-0.6 mEq/L may be adequate 2
- Toxicity risk: Begins at 1.5 mEq/L, with serious toxicity at >2.0 mEq/L 2
Laboratory Monitoring Schedule
Acute Phase Monitoring
During acute treatment, check serum lithium levels twice per week until levels and clinical condition stabilize. 2, 5, 1
- Draw blood samples 8-12 hours after the previous dose (standardized 12-hour level) for consistent interpretation 1, 3
- For once-daily dosing, the 24-hour trough level should serve as the control value 3
Maintenance Phase Monitoring
Once stable, monitor lithium levels and organ function every 3-6 months: 5
- Serum lithium levels: Every 2 months minimum in uncomplicated cases 1
- Renal function tests: Every 3-6 months 5
- Thyroid function tests: Every 3-6 months 5
Critical Safety Considerations
Drug Interactions and Contraindications
- Avoid NSAIDs: They increase lithium levels and toxicity risk 2
- Contraindications include: Significant renal impairment, cardiovascular disease, severe dehydration, and sodium depletion 2
Patient Education Requirements
- Educate patients about early signs of lithium toxicity to facilitate prompt intervention 5
- Emphasize maintaining adequate hydration, especially during intercurrent illness 2
- Warn that toxicity can occur at doses close to therapeutic levels 2, 6
Common Pitfalls to Avoid
- Do not rely solely on serum levels: Accurate patient evaluation requires both clinical assessment and laboratory analysis 1
- Adjust for formulation differences: Sustained-release preparations require targeting the upper therapeutic range (0.8-1.0 mEq/L) rather than 0.6-0.8 mEq/L for standard formulations 3
- Monitor more frequently during pregnancy: Lithium clearance increases by 30-50% in the last months of pregnancy, requiring dose adjustments 3