Lithium

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.

Lithium toxicity progresses in predictable stages tied to serum levels. The therapeutic range is 0.6–1.2 mEq/L, and a fine hand tremor at that level is an expected side effect. Toxicity usually begins above 1.5 mEq/L: early signs (about 1.5–2.0 mEq/L) are GI symptoms — nausea, vomiting, diarrhea — with a coarse tremor and muscle weakness. Moderate toxicity (about 2.0–2.5 mEq/L) escalates to ataxia, slurred speech, confusion, and blurred vision. Severe toxicity (over 2.5 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 patient 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.

Key Distinctions

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.

Clinical Use & Monitoring

Lithium is the gold-standard mood stabilizer for bipolar I disorder, effective for treating acute mania and preventing both manic and depressive episodes. It works by modulating neurotransmitter release and enhancing serotonin function, though its precise mechanism remains incompletely understood. The therapeutic serum level is 0.6–1.2 mEq/L, drawn 8–12 hours after the last dose (trough level). During acute mania, levels closer to 1.0–1.2 mEq/L are targeted; for maintenance, 0.6–1.0 mEq/L. Monitoring is intensive at first: serum lithium levels are drawn every 1–2 weeks during initiation and dose changes, then every 2–3 months once stable. Baseline and periodic labs include thyroid function (TSH, T3/T4), renal function (BUN, creatinine), and electrolytes — lithium is cleared almost entirely by the kidneys and directly affects thyroid activity. Adequate sodium and fluid intake are non-negotiable because lithium and sodium share renal reabsorption pathways. When sodium drops (from dehydration, low-sodium diets, or diuretics), the kidneys retain lithium in its place, driving levels up. This pharmacokinetic reality is the single most testable concept for this drug.

Key Distinctions

Don't confuse therapeutic monitoring labs (thyroid, renal, lithium trough) with toxicity signs — monitoring belongs here, toxicity recognition belongs in the sibling atom. Students mix up lithium's trough timing: the draw is 8–12 hours after the LAST dose, not 8–12 hours after the first morning dose. Lithium is not an antipsychotic — it doesn't treat psychosis directly and isn't grouped with typical or atypical agents.

Clinical Pearl

Lithium follows sodium: when sodium goes down, lithium goes up. Think of them as roommates competing for the same seat on the renal bus.