What to Do If Two Lithium Doses Are Taken Close Together
If a patient accidentally takes two lithium doses close together, skip the next scheduled dose entirely and resume the regular dosing schedule after that, while monitoring closely for signs of toxicity. 1, 2
Immediate Management Steps
Do not attempt to "make up" for the missed dose or adjust subsequent doses - simply return to the regular schedule after skipping one dose. 1, 3
Toxicity Monitoring Protocol
Monitor the patient for early signs of lithium toxicity over the next 24-48 hours, including: 1
- Fine tremor (more pronounced than baseline)
- Nausea and vomiting
- Diarrhea
- Increased confusion or drowsiness
Seek immediate medical attention if any of the following severe toxicity signs develop: 1, 2
- Coarse tremor (large, jerky movements)
- Ataxia (loss of coordination)
- Confusion or altered mental status
- Slurred speech
- Muscle twitching or rigidity
Clinical Context and Rationale
Lithium has an extremely narrow therapeutic index, meaning relatively minor increases in serum concentrations can induce serious adverse effects. 2, 4 The therapeutic range is typically 0.6-1.2 mEq/L, and concentrations even slightly above this can result in toxic reactions. 4, 5
Single daily dosing of lithium is associated with significant fluctuations in plasma concentrations throughout the day, with peak levels occurring 2-4 hours after administration. 3 Taking two doses close together creates an additive peak that substantially increases toxicity risk. 3, 4
When to Check Lithium Level
Obtain a stat lithium level if: 1, 5
- The patient develops any signs of toxicity
- The double dose occurred within 4-6 hours of each other
- The patient is on a higher maintenance dose (>900-1200 mg/day)
- The patient has renal impairment or is taking medications that affect lithium clearance (NSAIDs, ACE inhibitors, diuretics, thiazides) 4, 5
If checking a level, draw it 12 hours after the last dose taken to obtain a standardized trough level for comparison with previous values. 5
Prevention Strategies
Implement medication supervision through family members to prevent future dosing errors, particularly in patients with history of medication non-adherence or cognitive difficulties. 1, 6
Consider switching to once-daily dosing if the patient is currently on multiple daily doses - this reduces confusion about timing and has been shown to improve compliance without compromising efficacy. 3 Single daily administration may also reduce long-term renal damage risk compared to multiple daily dosing. 3
Prescribe limited quantities with frequent refills to minimize the risk of intentional overdose in patients with suicidal ideation. 1
Common Pitfalls to Avoid
Never advise the patient to induce vomiting or take extra fluids to "flush out" the lithium - lithium is renally cleared and these interventions are ineffective and potentially dangerous. 2, 4
Do not reduce subsequent doses below the prescribed amount - this risks subtherapeutic levels and mood destabilization. 1, 7 Simply skip one dose and resume the regular schedule. 3
Avoid assuming the patient is safe just because they feel fine initially - lithium toxicity symptoms can be delayed by several hours after ingestion, particularly with sustained-release formulations. 3, 7