How to convert lithium carbonate (lithium) 600mg sustained-release tablets from twice daily to once daily dosing at night?

Converting Lithium Carbonate Sustained-Release from Twice Daily to Once Daily Dosing

You can safely convert lithium carbonate sustained-release 600 mg twice daily (1200 mg total daily dose) to 1200 mg once daily at bedtime by administering the full daily dose as a single evening dose starting the next scheduled dose. This conversion maintains the same total daily dose while simplifying the regimen, which is supported by both FDA labeling and clinical pharmacology evidence.

Conversion Protocol

Immediate Conversion Approach

• Stop the morning dose immediately and give the entire 1200 mg daily dose at bedtime 1, 2
• The sustained-release formulation is specifically designed to allow once-daily dosing due to its pharmacokinetic profile with peak concentrations at 4-5 hours and elimination half-life of 18-36 hours 2
• No dose adjustment is required during conversion since the total daily dose remains unchanged at 1200 mg 1

Monitoring Requirements During Conversion

Serum lithium level monitoring:

• Draw serum lithium level 12 hours after the last twice-daily dose (baseline) 1
• After conversion, draw levels 24 hours after the once-daily evening dose (this becomes your new control value) 2
• Check serum lithium levels within 3-5 days after conversion to ensure therapeutic range is maintained 1
• Continue monitoring weekly for 2-3 weeks, then return to routine monitoring every 2 months once stable 1

Target therapeutic range:

• Maintain serum concentrations between 0.6-1.0 mEq/L for maintenance therapy 1, 2
• With sustained-release preparations, aim for the upper range (0.8-1.0 mEq/L) rather than 0.6-0.8 mEq/L used for standard formulations 2

Clinical Advantages of Once-Daily Dosing

• Improved compliance: Eliminates the problematic midday dose that patients frequently miss 2
• Reduced peak-to-trough fluctuations: Sustained-release formulations given once daily result in 30-50% reductions in peak plasma concentrations without major changes in total drug exposure 2
• Simplified regimen: Evening dosing is recommended by expert panels and improves long-term adherence 2

Important Caveats and Monitoring

Watch for signs of toxicity:

• Serum levels >1.5 mEq/L may cause mild, reversible toxic effects on kidney, liver, heart, and glands 3
• Levels >2.0 mEq/L can cause neurological symptoms including cerebellar dysfunction 3
• Monitor for confusion, speech impairment, tremor, or gastrointestinal symptoms 3, 4

Factors that may require dose adjustment:

• Elderly patients often require reduced dosages and may exhibit toxicity at levels ordinarily tolerated by younger patients 1
• Renal function changes can significantly affect lithium clearance (clearance decreases with aging) 2
• Drug interactions, particularly with NSAIDs, ACE inhibitors, or thiazide diuretics, can increase lithium levels 2, 4

Clinical assessment priorities:

• Do not rely solely on serum levels—accurate evaluation requires both clinical and laboratory analysis 1
• Monitor for therapeutic efficacy (mood stability) as well as adverse effects 1, 4
• Assess renal function, thyroid function, and electrolytes during the conversion period 4

Common Pitfalls to Avoid

• Do not reduce the total daily dose during conversion—the 1200 mg total remains the same, just given once instead of twice 1, 2
• Do not draw serum levels at the wrong time—once-daily dosing requires 24-hour trough levels, not 12-hour levels 2
• Do not assume immediate-release and sustained-release formulations are interchangeable—sustained-release allows once-daily dosing due to its pharmacokinetic profile 2
• Do not forget to counsel patients about taking the dose at the same time each evening for consistent serum levels 2