Should Lithium Be Stopped Due to Subtherapeutic Levels from Excessive Water Intake?
No, lithium should never be abruptly discontinued—instead, the excessive water intake must be corrected and lithium levels rechecked after stabilizing fluid intake. Abrupt lithium discontinuation dramatically increases relapse risk, with over 90% of noncompliant patients experiencing relapse versus 37.5% of compliant patients 1. The subtherapeutic level is a consequence of dilutional effects from excessive water consumption, not a reason to stop the medication 2.
Understanding the Mechanism
Excessive water intake dilutes serum lithium concentrations without actually reducing the total body lithium load 2. When a patient drinks 3+ liters of water daily beyond normal requirements, the increased renal clearance and dilutional effect artificially lowers measured lithium levels 2.
The therapeutic issue is fluid management, not lithium dosing 2. Lithium salt absorption requires at least 250 mL of water with each dose, and patients should maintain 1.5-3 liters daily depending on activity level and heat exposure 2. Exceeding this range creates the exact problem described in this case.
Immediate Management Algorithm
Step 1: Assess Current Fluid Intake (Days 1-3)
- Quantify exact daily water consumption including all beverages, using a 24-hour diary 2.
- Target fluid intake should be 1.5-2 liters daily for sedentary patients, up to 3 liters only during physical exertion or heat exposure 2.
- Identify triggers for excessive drinking: check fasting glucose to rule out hyperglycemia, review all medications for agents that stimulate thirst (clonidine, anticholinergics), and assess for psychogenic polydipsia 3.
Step 2: Correct Fluid Intake (Days 4-14)
Implement structured fluid restriction to 1.5-2 liters daily 2. Provide specific instructions: 500 mL with breakfast, 500 mL with lunch, 500 mL with dinner, and 250 mL at bedtime with lithium dose 2.
Continue lithium 900 mg at bedtime without dose adjustment during this correction phase 1, 4. The existing dose is appropriate; only the fluid intake requires modification 2.
Recheck lithium level after 5-7 days of normalized fluid intake 4. This allows sufficient time for steady-state equilibration after correcting the dilutional effect 4.
Step 3: Interpret Follow-Up Lithium Level (Day 14)
If lithium level reaches 0.6-1.0 mEq/L (therapeutic maintenance range): Continue current regimen with normalized fluid intake 4.
If lithium level remains <0.6 mEq/L despite corrected fluid intake: Increase lithium dose by 300 mg (to 1200 mg at bedtime) and recheck level in 5-7 days 4.
If lithium level exceeds 1.2 mEq/L: Reduce dose by 300 mg (to 600 mg at bedtime) and recheck in 5-7 days 4.
Critical Safety Considerations
Why Abrupt Discontinuation Is Dangerous
Withdrawal of maintenance lithium therapy dramatically increases relapse risk, especially within 6 months following discontinuation 1. The rebound phenomenon can precipitate severe manic episodes even in previously stable patients 1.
Lithium should be tapered gradually over 2-4 weeks minimum if discontinuation is truly necessary, never stopped abruptly 1. However, in this case, discontinuation is not indicated—only fluid management is needed 2.
Monitoring Requirements During Correction Phase
Check lithium level, renal function (BUN, creatinine), and thyroid function (TSH) at baseline before correcting fluid intake 4. This establishes whether renal impairment or other factors contribute to the subtherapeutic level 4.
Monitor for signs of lithium toxicity as fluid intake normalizes: fine tremor, nausea, diarrhea warrant immediate lithium level check 4. Coarse tremor, confusion, or ataxia require emergency evaluation 4.
Assess mood symptoms weekly during the correction phase 1. If manic or depressive symptoms emerge, this indicates inadequate lithium coverage and may require temporary adjunctive therapy (benzodiazepines for agitation, not antidepressants for depression) 1.
Common Pitfalls to Avoid
Never attribute subtherapeutic lithium levels to "treatment failure" without first correcting fluid intake 2. The medication is working appropriately; the patient's excessive water consumption is the problem 2.
Do not increase lithium dose before correcting fluid intake 2. This creates risk of toxicity once the patient returns to normal hydration 4, 5.
Avoid advising water restriction without simultaneously addressing sodium intake 3. If the patient consumes excessive sodium, restricting water alone causes unnecessary thirst and suffering 3. However, in this case, the primary issue is excessive water intake beyond physiologic needs 2.
Never use diuretics to manage fluid overload in lithium-treated patients 6. Thiazide diuretics increase lithium concentrations by 25-40%, creating severe toxicity risk 6. Loop diuretics have variable effects but should still be avoided 6.
Patient Education Points
Explain that lithium requires consistent, moderate fluid intake—neither excessive nor restricted 2. The goal is 1.5-2 liters daily for most patients 2.
Instruct the patient to take lithium at the end of a solid meal with at least 250 mL of water 2. This optimizes absorption and minimizes gastrointestinal side effects 2.
Warn against NSAIDs (ibuprofen, naproxen), which increase lithium levels and toxicity risk 4, 6. Acetaminophen is the preferred analgesic for lithium-treated patients 6.
Emphasize that abrupt lithium discontinuation causes relapse in >90% of patients 1. Any future dose adjustments must be gradual and supervised 1.
When to Consider Alternative Interventions
If excessive water intake persists despite behavioral interventions, evaluate for psychogenic polydipsia requiring psychiatric consultation 3.
If lithium levels remain subtherapeutic despite corrected fluid intake and dose optimization, verify medication adherence through pill counts or supervised administration 1. Noncompliance is a common cause of apparent treatment failure 1.
Only if the patient demonstrates true lithium non-response after adequate trial (therapeutic levels for 6-8 weeks) should alternative mood stabilizers be considered 1, 7. Options include valproate or combination therapy with lithium plus an atypical antipsychotic 1, 7.