Can you take both lithium carbonate and lithium controlled release (CR) simultaneously?

Lithium Carbonate and Lithium CR Should Not Be Taken Simultaneously

Taking both lithium carbonate and lithium controlled release (CR) formulations simultaneously is not recommended due to the risk of toxicity from overlapping peak concentrations and unpredictable serum levels. 1

Rationale for Avoiding Simultaneous Use

• Lithium has a narrow therapeutic index, making toxicity a significant concern when combining different formulations with different pharmacokinetic profiles 1, 2
• Different lithium formulations have distinct absorption patterns and peak concentration times:
  • Standard-release lithium carbonate reaches peak plasma concentration in 1-2 hours 1
  • Sustained/controlled-release formulations reach peak plasma concentration in 4-5 hours 1
• Combining formulations could lead to unpredictable serum lithium levels and increased risk of toxicity 2

Pharmacokinetic Differences Between Formulations

• Sustained-release formulations result in 30-50% reductions in peak plasma concentrations compared to immediate-release forms 1
• The bioavailability profiles of different extended-release lithium products are not equivalent:
  • Eskalith CR produces a 40% lower maximum plasma concentration than immediate-release lithium 3
  • Lithobid produces a 25% lower maximum plasma concentration than immediate-release lithium 3
• These differences make combining formulations potentially dangerous due to unpredictable absorption patterns 1, 3

Monitoring and Safety Considerations

• Lithium requires careful therapeutic monitoring due to its narrow therapeutic range 1
• KDIGO guidelines recommend regular monitoring of GFR, electrolytes, and drug levels for patients taking lithium 4
• Temporary discontinuation of lithium is recommended during serious intercurrent illness in patients with GFR <60 ml/min/1.73 m² 4
• Lithium toxicity can affect multiple organs, with the central nervous system being the primary site of toxicity 2

Proper Lithium Management

• Lithium dosing should be adjusted based on serum concentration drawn 12 hours after the last dose 1
• Therapeutic serum concentrations should generally be maintained between 0.6-0.8 mmol/L, though some clinicians prefer 0.8-1.2 mmol/L 1
• For sustained-release preparations, serum concentrations are typically kept in the upper range (0.8-1 mmol/L) rather than 0.6-0.8 mmol/L for standard formulations 1
• If a change in formulation is needed, it should be done with careful monitoring and under physician supervision 5

Alternative Approaches

• If considering a switch between formulations, consult with your prescribing physician who can evaluate your specific clinical situation 5
• Once-daily dosing of a single lithium formulation may improve tolerability and reduce side effects compared to twice-daily dosing 6
• Studies show that once-daily lithium dosing produces fewer renal adverse effects while maintaining similar efficacy to twice-daily dosing 6

Caution During Special Circumstances

• Lithium should be temporarily discontinued during serious illness that increases the risk of acute kidney injury 4
• Lithium use with electroconvulsive therapy (ECT) requires special consideration, as there are reports of acute brain syndrome when lithium is used concurrently with ECT 4
• If lithium discontinuation is necessary, a gradual taper is recommended (approximately 10% of the original dose per week) 5