Lithium — Toxicity & Patient Teaching
Lithium's therapeutic range is one of the narrowest in psychiatry — a single missed water bottle or new NSAID prescription can push a stable patient into life-threatening toxicity.
Core Concept
Lithium toxicity progresses in predictable stages tied to serum levels. The therapeutic range is 0.6–1.2 mEq/L. Early toxicity (1.2–1.5 mEq/L) presents with GI symptoms: nausea, vomiting, diarrhea, plus fine hand tremor and muscle weakness. Moderate toxicity (1.5–2.0 mEq/L) escalates to coarse tremors, ataxia, slurred speech, confusion, and blurred vision. Severe toxicity (>2.0 mEq/L) causes seizures, cardiac dysrhythmias, renal failure, and coma. Because lithium is a salt excreted entirely by the kidneys, anything that causes sodium loss or dehydration concentrates lithium: vomiting, diarrhea, excessive sweating, dehydration, sodium-restricted diets, and drugs like NSAIDs, ACE inhibitors, and thiazide diuretics. Patient teaching is the nurse's primary safety intervention. Teach the client to maintain consistent daily sodium and fluid intake (2–3 L/day), avoid new OTC NSAIDs without provider approval, report persistent GI symptoms immediately, and never double a missed dose. If toxicity is suspected, hold the dose, draw a level, and prepare for possible IV normal saline to promote renal excretion. There is no antidote — management is supportive, with hemodialysis reserved for severe cases.
Watch Out For
Don't confuse a fine hand tremor (expected therapeutic side effect) with a coarse tremor (early-moderate toxicity sign requiring immediate action). Students mix up lithium toxicity triggers with general drug interactions — the key principle is sodium-lithium competition: low sodium means the kidneys reabsorb more lithium. NSAIDs reduce renal lithium clearance directly — this is the highest-yield OTC drug interaction on the NCLEX.
Clinical Pearl
Think of lithium like a salt twin: wherever sodium goes, lithium follows. Lose sodium, keep lithium — that's how toxicity builds.
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