What is the starting dose of lithium for adults?

Starting Dose of Lithium for Adults

For adults under 60 years, start lithium at 450-900 mg per day (12-24 mmol), typically given as 300 mg twice daily or 450 mg once daily at bedtime, with the goal of achieving therapeutic serum levels of 0.8-1.0 mmol/L. 1

Age-Based Dosing Strategy

Adults Under 40 Years

• Initial dose: 450-900 mg daily (12-24 mmol) 1
• Target maintenance range: 925-1300 mg daily (25-35 mmol) once therapeutic levels are established 1
• Serum lithium should be drawn 12 hours after the last dose to guide adjustments 1

Adults 40-60 Years

• Initial dose: 450-900 mg daily (12-24 mmol) 1
• Target maintenance range: 740-925 mg daily (20-25 mmol) 1
• Lower doses are needed compared to younger adults due to age-related changes in lithium clearance 2

Adults Over 60 Years

• Initial dose: 300-450 mg daily (lower end of range) 1
• Target maintenance range: 550-740 mg daily (15-20 mmol) 1
• The dose required to achieve therapeutic levels decreases threefold between ages 40-95 years (e.g., 500 mg vs 1500 mg to achieve 1.0 mmol/L) 2
• More frequent monitoring is essential due to reduced renal function with aging 2

Therapeutic Target Levels

Aim for serum concentrations of 0.8-1.0 mmol/L for optimal efficacy, as this range has been proven superior to lower levels (0.4-0.6 mmol/L) in preventing relapse 1, 3

• Patients maintained at 0.8-1.0 mmol/L had only 13% relapse rate compared to 38% at 0.4-0.6 mmol/L 3
• The risk of relapse is 2.6 times higher with lower serum levels 3
• Some sources still recommend 0.6-0.8 mmol/L, but evidence favors the higher range for maintenance therapy 1

Dosing Schedule Considerations

Once-daily dosing at bedtime is preferred over divided doses for both compliance and potential renal protection 1, 4

• Once-daily dosing may be less harmful to kidneys than divided doses, as regenerative processes occur during periods of low lithium concentration 4
• Standard-release formulations peak at 1-2 hours; sustained-release at 4-5 hours 1
• With sustained-release preparations, maintain serum levels at 0.8-1.0 mmol/L rather than 0.6-0.8 mmol/L due to later peak concentrations 1

Critical Monitoring Requirements

Serum lithium levels must be checked 12 hours post-dose (or 24 hours for once-daily dosing) to guide all dose adjustments 1

• Lithium toxicity begins at 1.5 mEq/L and serious toxicity occurs at >2.0 mEq/L 5
• Initial monitoring should be twice weekly until levels and clinical condition stabilize 6
• Toxicity is closely related to serum concentrations and can occur at doses close to therapeutic levels 6, 5

Special Population Adjustments

Renal Impairment

• Patients with GFR <60 mL/min/1.73 m² require lower starting doses and more frequent monitoring 5
• 50% dose reduction is recommended for GFR <30 mL/min/1.73 m² 5
• Renal insufficiency is considered a relative contraindication, especially with sodium restriction 1

Pregnancy

• Lithium clearance increases 30-50% during the last months of pregnancy, requiring dose adjustments 1
• Lithium may cause fetal harm based on animal and human studies 6
• Lithium passes freely into breast milk 1

Common Pitfalls to Avoid

• Never split tablets to achieve doses, as this creates inconsistent dosing that makes therapeutic monitoring unreliable and dangerous 5
• Avoid starting at full maintenance doses—always begin at the lower initial range and titrate based on serum levels 1
• Do not use standard adult doses in elderly patients without adjustment, as they require substantially lower doses due to decreased renal clearance 2
• Never make concurrent medication changes during lithium initiation or dose adjustments 7