When do you check lithium levels after initiating therapy?

Lithium Level Monitoring After Initiation

Check serum lithium levels twice per week during the acute phase until both the serum concentration and clinical condition have stabilized. 1

Initial Monitoring Schedule

The FDA-approved labeling provides clear guidance for lithium monitoring after initiation:

• During acute phase: Measure serum lithium levels twice weekly until stabilization occurs 1
• Timing of blood draw: Collect samples 8-12 hours after the previous dose (immediately before the next dose) when concentrations are relatively stable 1
• Target therapeutic range during acute mania: 1.0-1.5 mEq/L 1

Critical Timing Considerations

For once-daily dosing regimens, the standard 12-hour sampling protocol does not apply:

• Serum levels should be drawn at 24 hours post-dose (not 12 hours) for patients taking sustained-release lithium once daily 2
• The 12-hour level can be 1.3 times higher than the actual trough level at 24 hours, potentially leading to underdosing if used as the reference point 2

Factors Requiring Earlier or More Frequent Monitoring

Several clinical situations necessitate more vigilant monitoring:

• Concurrent medications: NSAIDs and diuretics that interact with lithium require earlier and more frequent checks 3
• Renal function: Baseline renal function must be established before starting lithium, and any decline warrants immediate reassessment 3
• Symptoms of toxicity: Any signs of toxicity mandate immediate level checking regardless of the scheduled monitoring interval 3

Common Pitfalls to Avoid

• Failing to establish baseline renal function before initiating therapy is a critical error that can lead to toxicity 3
• Relying solely on serum levels: The FDA label explicitly states that "total reliance must not be placed on serum levels alone" - accurate evaluation requires both clinical and laboratory analysis 1
• Incorrect timing of blood draws: Drawing levels at the wrong time relative to dosing can result in misleading values and inappropriate dose adjustments 1, 2
• Overlooking intercurrent illness: Lithium should be temporarily suspended during illness, IV radiocontrast administration, bowel preparation, or prior to major surgery to prevent toxicity 3

Transition to Maintenance Monitoring

Once stabilized on lithium:

• Long-term maintenance: Check levels at least every 2 months in uncomplicated cases during remission 1
• Target maintenance range: 0.6-1.2 mEq/L 1