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Emergency and Acute Medicine – Lithium Poisoning
Basic description
Lithium is rapidly absorbed from the gastrointestinal tract, with peak serum levels occurring at 2–4 hours for regular-release formulations and 4–12 hours for sustained-release formulations. Distribution into tissues is slow, requiring at least 6 hours, and toxicity correlates with intracellular rather than serum concentrations. Lithium is not metabolized and is excreted unchanged by the kidneys, where it is reabsorbed in the proximal tubule via sodium transport mechanisms. It has a narrow therapeutic window, with therapeutic levels of 0.6–1.2 mEq/L measured after distribution. Elimination half-life is approximately 20–24 hours but is prolonged in chronic users.
Etiology
Toxicity occurs due to overdose or conditions that reduce renal clearance. Acute risk factors include dehydration and overdose, while chronic risk factors include advanced age, renal failure, congestive heart failure, hypertension, diabetes mellitus, low-salt diets, dose changes, and drug interactions. Medications that increase lithium levels include NSAIDs, thiazide diuretics, ACE inhibitors, phenytoin, tricyclic antidepressants, and phenothiazines.
Diagnosis: signs and symptoms
Acute toxicity is often less severe initially and dominated by gastrointestinal symptoms such as nausea, vomiting, diarrhea, and abdominal pain. Neurologic findings progress from fine tremor and weakness to ataxia, slurred speech, blurred vision, coarse tremor, hyperreflexia, confusion, seizures, coma, clonus, and extrapyramidal symptoms. Chronic toxicity more commonly produces neurologic manifestations, including parkinsonism, psychosis, and persistent cognitive deficits. Additional findings include nephrogenic diabetes insipidus, interstitial nephritis, hypothyroidism, leukocytosis, and dermatologic changes. Cardiac effects include QT prolongation, ST depression, T-wave flattening, and rarely serious dysrhythmias.
Essential workup
Serum lithium levels must be interpreted based on timing and type of exposure. Because distribution is delayed, levels should be repeated every 2 hours to assess trends. Acute toxicity may show high levels with minimal symptoms early, whereas chronic toxicity correlates more closely with symptoms at lower levels. Toxicity is generally associated with levels >4 mEq/L in acute ingestion, >3 mEq/L in acute-on-chronic ingestion, and >1.5 mEq/L in chronic toxicity.
Diagnosis tests and interpretation
Laboratory evaluation includes electrolytes, BUN, creatinine, glucose, and urinalysis to assess renal function and hydration status. Aspirin and acetaminophen levels should be checked if coingestion is suspected. ECG monitoring is indicated to detect conduction abnormalities.
Differential diagnosis
Consider lithium toxicity in patients with altered mental status and neuromuscular findings. Other considerations include hypoglycemia, cholinergic poisoning, heavy-metal toxicity, neuroleptic overdose, envenomation, and strychnine poisoning.
Treatment and stabilization
Initial management follows ABC principles with IV access, cardiac monitoring, and correction of hypoglycemia if present. Benzodiazepines are used for seizure control. Gastrointestinal decontamination is limited; activated charcoal is ineffective for lithium but may be given if coingestants are suspected. Whole-bowel irrigation with polyethylene glycol is recommended for sustained-release preparations if no contraindications exist. Aggressive isotonic saline hydration is the cornerstone of therapy, enhancing renal clearance and reducing tubular reabsorption. Diuretics and sodium bicarbonate are not recommended.
Enhanced elimination
Hemodialysis is indicated in severe cases, including progressive neurologic symptoms, renal insufficiency, significant altered mental status, ventricular dysrhythmias, or very high lithium levels. Suggested thresholds include >4–5 mEq/L in acute ingestion and >2.5–3 mEq/L in chronic toxicity. Rebound lithium levels due to redistribution are common, and repeat dialysis may be required until levels fall below 1 mEq/L.
Disposition and follow-up
Admission is required for symptomatic patients, those requiring hemodialysis, intentional ingestions, or persistently elevated lithium levels despite treatment. ICU admission is indicated for severe neurologic toxicity. Asymptomatic patients with decreasing levels and serum lithium <2 mEq/L may be discharged with close follow-up if ingestion was unintentional. Psychiatric consultation is required for intentional overdose, and outpatient follow-up should ensure appropriate dosing and monitoring.
Key points
Serum lithium levels must be interpreted in clinical context and timing of exposure. Hydration is the most effective initial therapy. Early recognition of chronic toxicity and timely use of hemodialysis can prevent permanent neurologic sequelae.
Basic description
Lithium is rapidly absorbed from the gastrointestinal tract, with peak serum levels occurring at 2–4 hours for regular-release formulations and 4–12 hours for sustained-release formulations. Distribution into tissues is slow, requiring at least 6 hours, and toxicity correlates with intracellular rather than serum concentrations. Lithium is not metabolized and is excreted unchanged by the kidneys, where it is reabsorbed in the proximal tubule via sodium transport mechanisms. It has a narrow therapeutic window, with therapeutic levels of 0.6–1.2 mEq/L measured after distribution. Elimination half-life is approximately 20–24 hours but is prolonged in chronic users.
Etiology
Toxicity occurs due to overdose or conditions that reduce renal clearance. Acute risk factors include dehydration and overdose, while chronic risk factors include advanced age, renal failure, congestive heart failure, hypertension, diabetes mellitus, low-salt diets, dose changes, and drug interactions. Medications that increase lithium levels include NSAIDs, thiazide diuretics, ACE inhibitors, phenytoin, tricyclic antidepressants, and phenothiazines.
Diagnosis: signs and symptoms
Acute toxicity is often less severe initially and dominated by gastrointestinal symptoms such as nausea, vomiting, diarrhea, and abdominal pain. Neurologic findings progress from fine tremor and weakness to ataxia, slurred speech, blurred vision, coarse tremor, hyperreflexia, confusion, seizures, coma, clonus, and extrapyramidal symptoms. Chronic toxicity more commonly produces neurologic manifestations, including parkinsonism, psychosis, and persistent cognitive deficits. Additional findings include nephrogenic diabetes insipidus, interstitial nephritis, hypothyroidism, leukocytosis, and dermatologic changes. Cardiac effects include QT prolongation, ST depression, T-wave flattening, and rarely serious dysrhythmias.
Essential workup
Serum lithium levels must be interpreted based on timing and type of exposure. Because distribution is delayed, levels should be repeated every 2 hours to assess trends. Acute toxicity may show high levels with minimal symptoms early, whereas chronic toxicity correlates more closely with symptoms at lower levels. Toxicity is generally associated with levels >4 mEq/L in acute ingestion, >3 mEq/L in acute-on-chronic ingestion, and >1.5 mEq/L in chronic toxicity.
Diagnosis tests and interpretation
Laboratory evaluation includes electrolytes, BUN, creatinine, glucose, and urinalysis to assess renal function and hydration status. Aspirin and acetaminophen levels should be checked if coingestion is suspected. ECG monitoring is indicated to detect conduction abnormalities.
Differential diagnosis
Consider lithium toxicity in patients with altered mental status and neuromuscular findings. Other considerations include hypoglycemia, cholinergic poisoning, heavy-metal toxicity, neuroleptic overdose, envenomation, and strychnine poisoning.
Treatment and stabilization
Initial management follows ABC principles with IV access, cardiac monitoring, and correction of hypoglycemia if present. Benzodiazepines are used for seizure control. Gastrointestinal decontamination is limited; activated charcoal is ineffective for lithium but may be given if coingestants are suspected. Whole-bowel irrigation with polyethylene glycol is recommended for sustained-release preparations if no contraindications exist. Aggressive isotonic saline hydration is the cornerstone of therapy, enhancing renal clearance and reducing tubular reabsorption. Diuretics and sodium bicarbonate are not recommended.
Enhanced elimination
Hemodialysis is indicated in severe cases, including progressive neurologic symptoms, renal insufficiency, significant altered mental status, ventricular dysrhythmias, or very high lithium levels. Suggested thresholds include >4–5 mEq/L in acute ingestion and >2.5–3 mEq/L in chronic toxicity. Rebound lithium levels due to redistribution are common, and repeat dialysis may be required until levels fall below 1 mEq/L.
Disposition and follow-up
Admission is required for symptomatic patients, those requiring hemodialysis, intentional ingestions, or persistently elevated lithium levels despite treatment. ICU admission is indicated for severe neurologic toxicity. Asymptomatic patients with decreasing levels and serum lithium <2 mEq/L may be discharged with close follow-up if ingestion was unintentional. Psychiatric consultation is required for intentional overdose, and outpatient follow-up should ensure appropriate dosing and monitoring.
Key points
Serum lithium levels must be interpreted in clinical context and timing of exposure. Hydration is the most effective initial therapy. Early recognition of chronic toxicity and timely use of hemodialysis can prevent permanent neurologic sequelae.
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