A 52-year-old man with bipolar disorder on lithium 900 mg daily presents with coarse tremor, confusion, ataxia, and diarrhea. Serum lithium level is 3.2 mEq/L (normal therapeutic range 0.6–1.2 mEq/L). He has normal renal function and is adequately hydrated. What is the drug of choice for acute management of his lithium toxicity?

Explanation

## Management of Acute Lithium Toxicity ### Severity Classification **Key Point:** Lithium toxicity severity is stratified by serum level and clinical presentation: - Mild toxicity: 1.5–2.5 mEq/L (tremor, nausea, diarrhea) - Moderate toxicity: 2.5–3.5 mEq/L (confusion, ataxia, coarse tremor) - Severe toxicity: >3.5 mEq/L (seizures, coma, cardiac arrhythmias, renal failure) ### Treatment Algorithm ```mermaid flowchart TD A[Lithium Toxicity Confirmed]:::outcome --> B{Serum Level & Symptoms?}:::decision B -->|Mild: 1.5-2.5 mEq/L| C[Supportive care + hydration]:::action B -->|Moderate: 2.5-3.5 mEq/L| D{Renal function normal?}:::decision B -->|Severe: >3.5 mEq/L| E[Hemodialysis STAT]:::urgent D -->|Yes| F[IV normal saline + monitor]:::action D -->|No| E C --> G[Stop lithium, recheck level]:::action F --> G E --> H[Repeat HD if rebound]:::action ``` ### Why Hemodialysis for This Patient **High-Yield:** This patient has: 1. **Serum level 3.2 mEq/L** = moderate-to-severe range 2. **Neurological signs** (confusion, ataxia, coarse tremor) = CNS involvement 3. **Gastrointestinal symptoms** (diarrhea) = systemic toxicity **Clinical Pearl:** Hemodialysis is indicated when: - Serum lithium >2.5 mEq/L with neurological symptoms - Serum lithium >3.5 mEq/L regardless of symptoms - Renal impairment (reduced clearance) - Altered mental status, seizures, or cardiac arrhythmias - Failure to improve with conservative measures ### Mechanism of Hemodialysis Efficacy **Key Point:** Lithium is: - A small ion (MW ~7 Da) → easily dialyzable - Water-soluble → removed by conventional hemodialysis - Has a large volume of distribution (0.5–1.0 L/kg) → rebound toxicity common after single session - Clearance by hemodialysis ~150–200 mL/min (vs. normal renal clearance 20–40 mL/min) **Warning:** Rebound phenomenon occurs 4–8 hours post-dialysis due to redistribution from intracellular to extracellular compartment. Repeat dialysis or continuous monitoring is essential. ### Supportive Measures (Adjunctive) - **IV normal saline:** Promotes renal excretion (NOT loop diuretics — these cause volume depletion and lithium reabsorption) - **Fluid and electrolyte balance:** Maintain euvolemia - **Stop lithium immediately:** No further doses - **Monitor:** Serum lithium q4–6h, ECG, renal function, electrolytes ### Why NOT the Other Options | Option | Why Incorrect | | --- | --- | | **Sodium bicarbonate** | No role in lithium toxicity. Bicarbonate is used for salicylate or tricyclic toxicity, not lithium. | | **Normal saline with loop diuretics** | Saline alone is appropriate for mild toxicity, but loop diuretics WORSEN lithium toxicity by causing volume depletion and increased proximal tubular reabsorption of lithium. | | **Activated charcoal** | Lithium is an inorganic ion; activated charcoal does not bind lithium. Charcoal is used for organic drug overdoses. | [cite:KD Tripathi 8e Ch 12]