Lithium Starting Dose for a 62-Year-Old Female
For a 62-year-old female, start lithium carbonate at 150–300 mg once daily (preferably in the evening), then titrate gradually based on renal function and serum levels. 1, 2
Age-Specific Dosing Rationale
- Elderly patients require substantially lower starting doses (150 mg/day) compared to younger adults (900 mg/day) due to increased risk of neurotoxicity, reduced renal clearance, and heightened sensitivity to lithium at standard serum concentrations. 2, 3
- Patients over 60 years typically need maintenance doses of only 15–20 mmol/day (550–740 mg lithium carbonate), which is roughly half the dose required for younger adults. 4
- Elderly patients often exhibit signs of toxicity at serum levels of 1.0–1.5 mEq/L that are ordinarily tolerated by younger patients, making conservative initial dosing essential. 3
Recommended Initiation Protocol
Step 1: Baseline Laboratory Assessment (Before First Dose)
- Obtain complete blood count, thyroid function tests (TSH, free T4), urinalysis, blood urea nitrogen, serum creatinine with eGFR, serum calcium, and pregnancy test (if applicable). 1, 2
- Baseline renal function is critical because lithium clearance decreases with aging, and renal impairment is a relative contraindication. 4, 5
Step 2: Initial Dosing
- Start with 150 mg once daily (evening dosing preferred) for patients ≥60 years or those with any degree of renal impairment (eGFR <60 mL/min/1.73 m²). 1, 2
- If renal function is normal (eGFR >60) and the patient is otherwise healthy, 300 mg once daily may be appropriate, but 150 mg is safer for initial assessment of tolerability. 2
- Never use split tablets to achieve lower doses—prescribe appropriately sized tablets (150 mg, 300 mg) to ensure consistent dosing. 2
Step 3: Early Monitoring and Titration
- Check serum lithium level 5–7 days after starting (drawn 12 hours post-dose for standard formulations, or 24 hours post-dose if using once-daily sustained-release). 1, 3, 4
- Also assess renal function (creatinine) and electrolytes at this early checkpoint, as the greatest changes in renal biomarkers occur within 2–4 weeks of initiation. 1
- Target serum level for maintenance therapy is 0.6–0.8 mEq/L in elderly patients; some may respond at even lower concentrations (0.2–0.6 mEq/L for augmentation strategies). 1, 4
- If the initial level is subtherapeutic and well-tolerated, increase by 150 mg increments every 5–7 days until reaching the target range. 1, 2
Step 4: Ongoing Monitoring
- Once stable, monitor lithium levels, renal function (BUN, creatinine), thyroid function (TSH), and urinalysis every 3–6 months. 1, 2
- If eGFR falls below 30 mL/min/1.73 m², increase monitoring to monthly and reassess the risk-benefit of continuing lithium. 1
- Increase monitoring frequency to every 1–2 weeks after any dose adjustment, addition of interacting medications (NSAIDs, ACE inhibitors, ARBs, thiazides), significant weight changes, or intercurrent illness. 1
Special Considerations for This Population
Renal Function Adjustments
- In moderate renal impairment (eGFR 30–60 mL/min/1.73 m²), start at 50% of the usual adult dose (i.e., 150 mg once daily) and extend the dosing interval rather than increasing individual dose amounts. 1
- Lithium clearance is considerably reduced with aging, and standard twice- or three-times-daily dosing may need conversion to once-daily or every-other-day dosing in patients with impaired renal function. 1, 4
Drug Interactions
- Patients taking NSAIDs, ACE inhibitors, ARBs, or thiazide diuretics require more frequent monitoring due to elevated lithium toxicity risk from reduced renal clearance. 1, 2
- Avoid concomitant NSAIDs when possible, as they significantly increase lithium levels and nephrotoxicity risk. 1
Formulation Selection
- Once-daily dosing with sustained-release formulation (preferably evening) may improve compliance and reduce side effects, though it results in 30–50% lower peak plasma concentrations without major changes in total exposure. 4
- With sustained-release preparations, maintain serum concentrations in the upper therapeutic range (0.8–1.0 mEq/L) rather than 0.6–0.8 mEq/L for standard formulations, due to the later peak. 4
Critical Safety Warnings
- Toxicity begins at serum levels ≥1.5 mEq/L, with serious toxicity at >2.0 mEq/L; early signs include tremor, nausea, diarrhea, and polyuria-polydipsia. 2
- Serum levels >2.0 mEq/L may cause neurological symptoms (cerebellar dysfunction, confusion, ataxia), and prolonged intoxication can cause permanent brain damage. 6
- Elderly patients are at higher risk for neurotoxicity even at therapeutic levels, so err on the side of lower dosing and more frequent monitoring. 3, 5
- Maintain hydration during intercurrent illness and check levels more frequently, as dehydration and sodium depletion increase lithium retention and toxicity risk. 1
Common Pitfalls to Avoid
- Do not start at 300 mg three times daily (900 mg/day) in elderly patients—this standard adult dose is inappropriate and dangerous for those over 60. 2, 3
- Do not wait beyond 7–8 days to check the first lithium level, as steady state is achieved by this time and dose adjustments can be made safely. 1
- Do not split lithium tablets to achieve target doses, as this creates inconsistent dosing that makes therapeutic monitoring unreliable and dangerous. 2
- Do not rely solely on serum levels—accurate patient evaluation requires both clinical assessment and laboratory analysis. 3
- Do not discontinue lithium abruptly if it becomes necessary to stop; taper gradually over 2–4 weeks minimum to minimize rebound risk. 1
Expected Timeline
- Lithium requires 7–8 days to reach steady-state serum concentrations regardless of dosing schedule, with an elimination half-life of 18–36 hours. 1, 4
- Therapeutic effects become apparent after 1–2 weeks at therapeutic levels, with full response requiring 4–6 weeks. 2
- Brain lithium concentrations are approximately 50% of serum concentrations (occasionally 75–80%), and are weakly correlated with serum levels. 4