Can you take lithium (lithium) CR 450mg twice daily (BID) and lithium carbonate 300mg twice daily (BID) simultaneously?

Taking Lithium CR 450mg BID and Lithium Carbonate 300mg BID Simultaneously

No, you should not take lithium CR 450mg twice daily and lithium carbonate 300mg twice daily simultaneously, as this combination would likely lead to lithium toxicity.

Understanding Lithium Formulations and Dosing

• Lithium is available in different formulations including immediate-release (standard) and controlled-release (CR) preparations 1
• Both formulations contain lithium as the active ingredient but differ in their pharmacokinetic properties:
  • Standard-release lithium reaches peak plasma concentration in 1-2 hours 1
  • Controlled-release formulations reach peak plasma concentration in 4-5 hours 1
• Taking both formulations simultaneously would result in a total daily lithium dose of 1500mg (750mg twice daily), which exceeds typical therapeutic dosing for most patients 1

Risks of Combined Lithium Formulations

• Lithium has a narrow therapeutic index, requiring careful dosing to maintain serum levels between 0.6-1.0 mM 2, 3
• Serum lithium levels above 1.5 mM may cause mild and reversible toxic effects on kidney, liver, heart, and glands 3
• Levels above 2.0 mM can cause neurological symptoms including cerebellar dysfunction 3
• Prolonged lithium intoxication above 2.0 mM can cause permanent brain damage 3

Appropriate Lithium Dosing

• The usual maintenance daily dose of lithium depends on age:
  • 25-35 mmol (925-1300 mg) for patients aged <40 years
  • 20-25 mmol (740-925 mg) for those aged 40-60 years
  • 15-20 mmol (550-740 mg) for patients aged >60 years 1
• Initial recommended dose is typically 12-24 mmol (450-900 mg) per day 1
• Lithium dosage should be adjusted based on serum concentration drawn 12 hours after the last dose 1

Alternative Dosing Approaches

• Once-daily dosing of lithium has been shown to be as effective as twice-daily dosing with potentially fewer side effects 4, 5
• A single-daily dose of lithium may lead to better patient compliance due to reduced renal adverse effects 4
• When using sustained-release preparations, serum concentrations should be maintained in the upper therapeutic range (0.8-1.0 mmol/L) 1

Monitoring and Safety Considerations

• Regular monitoring of serum lithium levels is essential due to lithium's narrow therapeutic range 2, 1
• Lithium clearance can be affected by:
  • Sodium depletion (from sweating, diarrhea, or low-salt diet)
  • Concomitant medications (NSAIDs, ACE inhibitors, diuretics)
  • Renal function changes
  • Age-related changes 2
• Patients should maintain adequate fluid intake (2500-3000 mL daily) and normal salt intake 2

Bioequivalence Considerations

• Different lithium formulations are not bioequivalent:
  • Extended-release formulations (like Eskalith CR) produce approximately 40% lower maximum plasma concentrations than immediate-release formulations 6
  • Different extended-release products may have up to 23% difference in maximum plasma concentrations 6
• This lack of bioequivalence further increases the risk of unpredictable serum levels when combining different formulations 6

If you're currently taking one formulation and considering switching to another, consult with your healthcare provider to establish an appropriate dosing regimen based on your specific needs and serum lithium monitoring.