What is the recommended dose of lithium (lithium carbonate) for a 15-year-old?

Lithium Dosing for a 15-Year-Old

For a 15-year-old, use adult dosing protocols starting with 12-24 mmol (450-900 mg) of lithium carbonate per day divided into 2-3 doses, targeting serum levels of 0.6-0.8 mmol/L measured 12 hours post-dose. 1

Initial Dosing Strategy

• Start with 450-900 mg daily (12-24 mmol) of lithium carbonate, typically divided into twice-daily or three-times-daily dosing 1
• The specific starting dose within this range depends on body weight, with heavier adolescents requiring doses toward the upper end 1
• Once-daily evening dosing with sustained-release formulations is increasingly recommended for improved compliance, though twice-daily remains well-established 1

Target Therapeutic Range

• Maintain serum concentrations between 0.6-0.8 mmol/L for most indications 1
• Some clinicians still favor 0.8-1.2 mmol/L, but the lower range minimizes side effects while maintaining efficacy 1
• For augmentation of antidepressants, even lower levels (0.2-0.6 mmol/L) may be adequate 2
• Avoid levels >1.5 mmol/L as this increases risk of toxicity affecting kidney, liver, heart, and glands 3

Critical Monitoring Requirements

Baseline Testing (Before Starting)

• Complete blood count 2
• Thyroid function tests (TSH, free T4) 2
• Renal function (BUN, creatinine, GFR) 2
• Serum electrolytes including calcium 2
• Urinalysis 2
• ECG to check for QT prolongation 4

Ongoing Monitoring

• Serum lithium levels drawn 12 hours after the last dose (or 24 hours for once-daily dosing) 1
• Renal function tests every 3-6 months 4
• Thyroid function tests every 3-6 months 4
• Serum calcium annually 4
• Liver function tests at 1 month, then every 6 months 4

Formulation Considerations

• Standard-release formulations reach peak plasma concentration at 1-2 hours with bioavailability of 80-100% 1
• Sustained-release formulations peak at 4-5 hours and reduce peak concentrations by 30-50%, which may improve tolerability 1
• With sustained-release preparations, target the upper therapeutic range (0.8-1.0 mmol/L) rather than 0.6-0.8 mmol/L due to the delayed peak 1

Important Safety Considerations

Early Toxicity Warning Signs

• Tremor, nausea, diarrhea, and polyuria-polydipsia are early indicators of toxicity 4
• Levels >2.0 mmol/L can cause neurological symptoms including cerebellar dysfunction 3
• Prolonged intoxication >2 mmol/L can cause permanent brain damage 3

Drug Interactions and Contraindications

• Avoid NSAIDs as they increase lithium levels and toxicity risk 2
• Significant renal impairment (GFR <60 mL/min/1.73 m²) requires dose reduction and more frequent monitoring 2
• Severe dehydration and sodium depletion are contraindications 2
• Maintain adequate hydration, especially during illness 2

Practical Dosing Algorithm

1. Verify no contraindications through baseline laboratory testing 2
2. Start with 450-600 mg daily for average-weight adolescents, divided into 2 doses 1
3. Check serum level after 5-7 days (5 half-lives to reach steady state, given 18-36 hour half-life) 1
4. Adjust dose based on serum level: if below 0.6 mmol/L, increase by 150-300 mg; if above 0.8 mmol/L, decrease by 150-300 mg 1
5. Recheck levels 5-7 days after each adjustment until therapeutic range achieved 1
6. Once stable, monitor levels monthly initially, then every 3-6 months 4