What is the best course of action for a patient with a subtherapeutic lithium level of 0.2, who recently started lithium 150mg bid, considering potential steady-state concentration and normal renal function?

Increase the Lithium Dose

You should increase the lithium dose now rather than redrawing the lab, as the patient has not yet reached steady-state and the current level of 0.2 mEq/L is subtherapeutic even for augmentation strategies.

Rationale for Dose Increase

Steady-State Has Not Been Reached

• Lithium has an elimination half-life of 18-36 hours, meaning steady-state is typically achieved after 5-7 days of consistent dosing 1
• Your patient started lithium on one date and had labs drawn shortly after—this timing is insufficient to reach steady-state concentrations 1
• Redrawing the lab at this point would yield similarly low results and unnecessarily delay therapeutic intervention 1

Current Level is Subtherapeutic for All Indications

• The measured level of 0.2 mEq/L falls below even the lowest therapeutic range for any indication 2
• For lithium augmentation of antidepressants, the American Academy of Family Physicians recommends blood levels of 0.2-0.6 mEq/L, but your patient is at the absolute floor of this range 2
• For standard bipolar maintenance therapy, therapeutic concentrations should be maintained between 0.6-0.8 mEq/L, with some experts favoring 0.8-1.2 mEq/L 1
• The therapeutic range broadly spans 0.30-1.30 mEq/L, with toxicity risk beginning at 1.5 mEq/L 3

Recommended Dosing Strategy

Appropriate Dose Escalation

• Increase the lithium dose to 300 mg twice daily (600 mg/day total) 1
• The initial recommended dose is typically 450-900 mg per day depending on age and body weight, so 600 mg/day represents a reasonable middle ground 1
• For elderly patients or those with reduced renal function, the starting dose of 150 mg/day is appropriate, but titration upward is expected 2, 4

Timing of Next Laboratory Draw

• Recheck the lithium level 5-7 days after the dose increase to allow adequate time to reach steady-state 1
• Draw the level 12 hours after the last dose (standardized 12-hour trough level) for accurate interpretation 1, 3
• During the acute phase of treatment, serum concentrations should be checked twice per week until levels and clinical condition stabilize 2

Critical Monitoring Considerations

Renal Function Assessment

• Ensure baseline renal function (GFR, creatinine) was checked before initiating lithium 2
• Patients with GFR < 60 ml/min/1.73 m² require lower doses and more frequent monitoring 2, 4
• If GFR < 30 ml/min/1.73 m², a 50% dose reduction from standard dosing is recommended 2, 4

Common Pitfalls to Avoid

• Do not wait for steady-state from the current inadequate dose—this delays therapeutic benefit without clinical justification 1
• Avoid checking lithium levels at non-standardized times, as this makes interpretation unreliable 1, 3
• Ensure the patient maintains adequate hydration and avoids NSAIDs, which can increase lithium levels and toxicity risk 2
• Do not split tablets to achieve intermediate doses, as this creates inconsistent dosing and unreliable monitoring 4

Safety Monitoring

• Lithium toxicity is closely related to serum concentrations and can occur at doses close to therapeutic levels 2, 4
• Serious toxicity occurs at levels >2.0 mEq/L, but risk begins at 1.5 mEq/L 2, 4
• Monitor for early signs of toxicity including tremor, confusion, and gastrointestinal symptoms 2