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Difficulty: MediumMonitoring and Treatment Evaluation

During a routine medication management visit, a 52-year-old man reports a three-day history of worsening nausea, diarrhea, and unsteadiness. He was diagnosed with bipolar I disorder five years ago and has maintained psychiatric stability on a regimen of lithium carbonate. Two weeks prior to this visit, his primary care provider initiated hydrochlorothiazide for newly diagnosed primary hypertension. His temperature is 37.1°C (98.8°F), blood pressure is 122/78 mmHg, and pulse is 86/min. Neurological examination reveals a prominent coarse tremor in both hands and mild ataxia during tandem gait. Which of the following is the most appropriate next step in the management of this patient?

  1. Withhold lithium and obtain a stat serum lithium levelAnswer
  2. B
    Discontinue hydrochlorothiazide and continue the current lithium regimen
  3. C
    Prescribe propranolol for symptomatic management of the tremor
  4. D
    Order a non-contrast CT scan of the head
  5. E
    Maintain the current medication regimen and recommend aggressive oral hydration

Answer

The most appropriate next step is to withhold lithium and obtain a stat serum lithium level.
The correct management is to withhold lithium and obtain a stat serum lithium level. This patient is exhibiting classic signs of acute-on-chronic lithium toxicity (nausea, diarrhea, coarse tremor, ataxia), precipitated by the recent addition of hydrochlorothiazide. Thiazide diuretics decrease renal lithium clearance by inducing volume depletion, which stimulates compensatory proximal tubular reabsorption of sodium and lithium. The immediate next step in evaluating and modifying this treatment regimen is to withhold the offending agent to prevent further accumulation and obtain a serum level to confirm the diagnosis and guide subsequent management (e.g., intravenous hydration, possible hemodialysis).

Step-by-Step Solution

1
Identify the patient's acute clinical syndrome.
The patient presents with new-onset gastrointestinal symptoms (nausea, diarrhea), a coarse tremor, and ataxia.
These are classic systemic and neurological signs of lithium toxicity, which differ from the benign fine tremor seen at therapeutic levels.
2
Determine the precipitating cause of the syndrome.
The recent addition of hydrochlorothiazide (a thiazide diuretic).
Thiazide diuretics induce volume depletion, which stimulates compensatory proximal tubular reabsorption of both sodium and lithium, leading to toxic systemic accumulation of lithium.
3
Select the safest immediate intervention for treatment evaluation.
Withhold the lithium and measure serum lithium levels.
Further lithium administration is contraindicated during active toxicity. A serum level is required to confirm the diagnosis and determine the need for advanced therapies such as intravenous hydration or hemodialysis.

Key Concept

Initiation of thiazide diuretics in patients taking lithium decreases renal clearance of lithium, precipitating acute-on-chronic toxicity characterized by gastrointestinal distress, coarse tremors, and ataxia. Management requires immediate withholding of lithium and measuring serum levels.
Estimated Time:1m 15s
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Topics

Monitoring and Treatment Evaluation

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