Situation: A 40-year-old man with bipolar I disorder has taken lithium carbonate 450 mg orally twice daily for 2 years. His trough serum lithium levels have been 0.8–0.9 mEq/L (therapeutic range 0.6–1.2 mEq/L; toxic above 1.5 mEq/L). He is followed at an outpatient mental health clinic. He comes to the clinic after 2 days of vomiting and watery stools. He has a coarse hand tremor and walks unsteadily. A serum lithium level drawn this morning, 12 hours after his last dose, is 1.3 mEq/L. Which action should the nurse take?

Vomiting and diarrhea cause dehydration, which raises lithium levels. Coarse tremor and ataxia are signs of mild-to-moderate toxicity, and the level of 1.3 mEq/L is already above the 0.6–1.2 mEq/L range. Toxicity can occur below 1.5 mEq/L, so the nurse holds the dose and notifies the prescriber rather than relying on the number alone.

Clinical situation
A patient on long-term lithium for bipolar I disorder presents with gastrointestinal fluid loss, a coarse tremor, and an unsteady gait. The 12-hour trough level has risen to 1.3 mEq/L, which is above the stated therapeutic range of 0.6–1.2 mEq/L even though it remains below the classic toxic threshold of 1.5 mEq/L. The correct nursing action is to hold the next lithium dose and notify the prescriber immediately, because toxicity is a clinical diagnosis supported by the level, not a decision made solely by crossing a single cutoff.

Why dehydration matters more than the number alone
Lithium is handled almost entirely by the kidneys, and its clearance depends heavily on sodium and water balance. Vomiting and watery diarrhea produce volume depletion, which triggers renal sodium and water retention. Because lithium is reabsorbed in the proximal tubule along with sodium, dehydration reduces lithium clearance and raises the serum concentration even when the prescribed dose has not changed ^[3]. The patient had been stable at 0.8–0.9 mEq/L for two years, so the jump to 1.3 mEq/L after only two days of GI losses reflects a pharmacokinetic shift rather than a dosing error. Continuing the usual dose while the patient is still volume-depleted would allow the level to climb further.

Clinical signs indicate neurotoxicity, not just a lab trend
A fine hand tremor is a common, often benign lithium side effect at therapeutic levels. A coarse tremor is different: it is a neurological warning sign. Combined with ataxia, it points to central nervous system toxicity. Lithium crosses the blood–brain barrier slowly, so brain tissue concentrations can lag behind serum levels and remain elevated longer. This explains why patients may show neurological symptoms at serum levels that are only modestly elevated, and why clinical assessment must guide urgency. The case literature reinforces that lithium’s narrow therapeutic index makes patients vulnerable to toxicity after even routine physiological stressors or medication changes . In severe cases, neurotoxicity can progress to impaired consciousness, myoclonus, and structural brain lesions such as cytotoxic lesions of the corpus callosum . The nurse should therefore interpret the coarse tremor and ataxia as early but real toxicity signals requiring immediate interruption of the drug.

Why holding the dose is the priority action
The prescriber needs to know three things at once: the patient has acute GI fluid loss, the lithium level has risen above the therapeutic range, and neurological signs of toxicity are present. Holding the next dose prevents further drug accumulation while the prescriber decides whether dose reduction, temporary discontinuation, or more aggressive management is needed. This is safer than reducing to once-daily dosing without prescriber input, because the patient’s renal clearance is currently unstable. It is also safer than waiting one week to recheck, because lithium toxicity can worsen rapidly when dehydration persists. Oral fluids may help restore volume, but they are an adjunct, not a substitute for stopping the drug and obtaining medical direction.

Option	Why it is incorrect or unsafe
1. Reduce to one dose daily until vomiting stops	Independent dose adjustment is outside nursing scope; the level is already above range and toxicity signs are present.
2. Continue usual dose because level is below 1.5 mEq/L	Treats 1.5 mEq/L as the only threshold; toxicity can occur below it, especially with neurological symptoms.
3. Hold the next dose and notify the prescriber	Correct: stops further accumulation and initiates timely medical management.
4. Encourage oral fluids and recheck in 1 week	Delays reassessment too long; does not address ongoing drug intake during active toxicity.

Key point! Lithium toxicity is diagnosed by the combination of clinical signs and serum level trend, not by waiting for the level to cross 1.5 mEq/L. A rising level above the patient’s usual therapeutic range, especially with coarse tremor and ataxia, requires holding the dose and notifying the prescriber.

Watch out! Dehydration from vomiting and diarrhea is a common trigger for lithium toxicity in previously stable patients. The dose may not have changed, but the kidney’s ability to clear lithium has.