Lithium poisoning, also known as lithium toxicity, occurs when the mood-stabilizing medication lithium builds up to harmful concentrations in the body. It is primarily prescribed to manage bipolar disorder, a condition characterized by significant mood swings. While effective in reducing episodes of mania and lowering suicide risk, lithium has a narrow therapeutic window, meaning there is a small difference between a safe and a toxic dose.
Causes of Lithium Toxicity
Lithium toxicity can arise from two main scenarios: acute or chronic toxicity. Acute toxicity occurs when a single large dose of lithium is ingested, overwhelming the body’s ability to process and eliminate the drug.
Chronic toxicity develops gradually as lithium accumulates in the body over time. This can occur even when taking the prescribed daily dose, as various factors can impair the body’s ability to excrete lithium. The kidneys eliminate about 95% of lithium from the body, so impaired kidney function significantly increases toxicity risk. Dehydration, often due to vomiting, diarrhea, fever, or inadequate fluid intake, can also concentrate lithium levels in the blood. Interactions with other medications, such as NSAIDs (e.g., ibuprofen), diuretics, and certain ACE inhibitors, can reduce lithium excretion and lead to elevated levels. Significant changes in salt intake, particularly a low-sodium diet, can also affect how the kidneys handle lithium, increasing its reabsorption and potentially leading to toxicity.
Identifying the Symptoms
Symptoms of lithium toxicity vary widely in presentation and severity, often correlating with the concentration of lithium in the blood. Recognizing these signs is important, as they can develop gradually, especially in cases of chronic toxicity.
Mild symptoms (1.5-2.5 mEq/L) typically include gastrointestinal issues such as nausea, vomiting, stomach pains, and diarrhea. Individuals may also experience fatigue, muscle weakness, drowsiness, and a fine tremor in the hands. These early signs can sometimes be mistaken for general illness or medication side effects.
As lithium levels rise, moderate symptoms (2.5-3.5 mEq/L) may emerge. These can include worsening tremors, confusion, agitation, and muscle twitching. Slurred speech, balance issues, and uncontrolled eye movements may also become apparent.
Severe lithium toxicity (above 3.5 mEq/L) can manifest as seizures, coma, and irregular heartbeats. Kidney failure and dangerously low blood pressure are also possible in these serious cases. Immediate medical attention is necessary if severe symptoms develop.
Medical Intervention and Treatment
Diagnosing lithium poisoning begins with a thorough medical evaluation and blood tests to measure serum lithium concentration. These tests are often repeated every 4 to 6 hours to monitor the lithium level’s trend. Tests to assess kidney function, such as creatinine and BUN levels, are also performed, as the kidneys are the primary route of lithium excretion.
Upon confirmation of lithium toxicity, the first step is to immediately stop lithium administration. For mild to moderate cases, supportive care is often sufficient, which includes ensuring the patient is well-hydrated. Administering intravenous (IV) fluids, such as saline, helps the kidneys flush out the excess lithium more effectively. This rehydration also corrects any fluid or electrolyte imbalances that may have contributed to the toxicity.
In severe cases, or if kidney function is significantly impaired, hemodialysis may be necessary. This procedure rapidly filters lithium directly from the blood, offering a quick and effective way to lower dangerously high levels. The decision to initiate hemodialysis depends on the patient’s clinical condition, the severity of symptoms, and lithium levels, especially if they exceed 4.0 mEq/L in chronically treated patients or 6.0 mEq/L in any patient.
Prevention Strategies
Preventing lithium toxicity involves consistent monitoring and proactive patient engagement. Regular blood tests to check serum lithium levels are fundamental, typically performed every 3 months once levels are stable, but more frequently during initiation or dose adjustments. These tests ensure lithium concentrations remain within the safe therapeutic range (0.6-1.2 mEq/L).
Maintaining consistent hydration is another important preventive measure. Patients should drink adequate fluids, especially during periods of increased sweating, such as hot weather, exercise, or illness accompanied by fever, vomiting, or diarrhea. Stable salt intake is also advised, as abrupt changes in dietary sodium can influence lithium levels.
Patients should avoid taking other medications that can interfere with lithium excretion without consulting their doctor. This includes NSAIDs, as well as certain diuretics and ACE inhibitors. Informing all healthcare providers about lithium use is also important to prevent potentially harmful drug interactions.