A 35-year-old woman with bipolar I disorder has been stable on lithium 750 mg twice daily (serum level 0.9 mEq/L) for 18 months. She develops acute gastroenteritis with vomiting and diarrhea. Regarding lithium management during acute illness, all of the following statements are correct EXCEPT:

Explanation

## Lithium Management in Acute Illness ### Key Point: **During acute dehydration (vomiting, diarrhea), lithium dosing must be reduced or temporarily held—NOT continued at the same dose.** Continuing lithium during volume depletion significantly increases the risk of toxicity. ### Correct Answer Rationale Option 2 is **incorrect** because lithium should **NOT** be continued at the same dose during acute gastroenteritis. Dehydration causes increased proximal tubular reabsorption of lithium, leading to elevated serum levels. The standard recommendation is to **hold or reduce the dose** until fluid balance is restored, then resume at the original dose. ### Why Each Correct Option Is True | Statement | Mechanism | |-----------|----------| | **Dehydration ↑ Li⁺ levels** | Lithium is filtered at the glomerulus and reabsorbed in the proximal tubule alongside Na⁺. Volume depletion activates the renin-angiotensin-aldosterone system, increasing proximal tubular reabsorption of both Na⁺ and Li⁺, raising serum lithium concentration | | **NSAIDs & thiazides ↑ Li⁺** | NSAIDs reduce renal blood flow and GFR; thiazides promote Na⁺ and Li⁺ reabsorption. Both increase serum lithium levels and toxicity risk | | **Check level in 24–48 hrs** | If GI symptoms persist, serum lithium should be monitored to detect early elevation before clinical toxicity develops | ### Clinical Pearl: **High-Yield:** The classic triad of **dehydration + NSAIDs + lithium** is a common cause of lithium toxicity in clinical practice. Always counsel patients to avoid NSAIDs and maintain adequate hydration. ### Management Algorithm During Acute Illness ```mermaid flowchart TD A[Acute gastroenteritis in lithium patient]:::outcome --> B{Vomiting/diarrhea present?}:::decision B -->|Yes| C[HOLD or REDUCE lithium dose]:::action B -->|No| D[Continue lithium as usual]:::action C --> E[Encourage oral rehydration]:::action E --> F{Symptoms resolve in 1-2 days?}:::decision F -->|Yes| G[Resume original lithium dose]:::action F -->|No| H[Check serum lithium level]:::action H --> I{Level elevated?}:::decision I -->|Yes| J[Reduce dose, increase monitoring]:::action I -->|No| K[Resume original dose]:::action J --> L[Recheck level in 3-5 days]:::action ``` ### Mnemonic: **LITHIUM in Acute Illness** - **L**ower the dose (or hold temporarily) - **I**ncreased reabsorption (from dehydration) - **T**hink NSAIDs and diuretics (avoid) - **H**ydration status (assess and maintain) - **I**ncrease monitoring (serum levels) - **U**nderstand renin-angiotensin activation - **M**onitor for tremor, confusion, ataxia (toxicity signs) ### Warning: Do NOT assume that maintaining therapeutic serum levels during acute illness is safe. The risk of toxicity is determined not only by serum concentration but also by **acuity of rise** and **tissue distribution**. Rapid increases in serum lithium during dehydration can cause symptomatic toxicity even at nominally "therapeutic" levels. [cite:Kaplan & Sadock's Synopsis of Psychiatry 11e Ch 31; Harrison 21e Ch 406]