Lithium is a naturally occurring element and a highly effective medication for stabilizing mood in people with disorders such as bipolar disorder. It is a long-standing treatment often prescribed to manage acute manic episodes and prevent the recurrence of mood swings. Lithium has a narrow therapeutic window, meaning the dosage required for a therapeutic effect is only slightly lower than the dose that can cause toxicity. This small margin necessitates careful monitoring, as high levels in the bloodstream can lead to lithium poisoning. Recognizing the signs of toxicity is paramount for anyone taking this medication.
How Lithium Toxicity Develops
Lithium toxicity occurs when the amount of the drug in the body exceeds safe limits, leading to cell and organ damage. The body primarily relies on the kidneys to excrete lithium, with approximately 95% of the drug eliminated through urine. Because lithium clearance is dependent on kidney function, any disruption to this system can rapidly lead to elevated lithium levels in the bloodstream and tissues.
Toxicity can develop in two primary ways: acute overdose or chronic accumulation. An acute overdose involves ingesting a large amount of lithium at once, which causes high blood concentrations. Chronic toxicity, often considered more dangerous, happens when lithium gradually builds up over days or weeks, even if the person is taking a stable dose.
Several factors can impair the body’s ability to excrete lithium, promoting chronic accumulation. Dehydration, caused by conditions like vomiting, diarrhea, fever, or intense exercise, is a common trigger. This occurs because the kidneys reabsorb lithium more aggressively when the body is trying to conserve water and sodium. A low-sodium diet can also increase lithium reabsorption in the kidneys, raising the concentration in the blood.
Drug Interactions
Drug interactions represent a significant risk factor that can push lithium levels into the toxic range. Certain common medications interfere with the kidneys’ ability to filter lithium, including nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, and some diuretics. Angiotensin-converting enzyme (ACE) inhibitors, used to treat high blood pressure, can also reduce lithium clearance. Adding or stopping these medications without adjusting the lithium dose can inadvertently cause chronic toxicity.
Recognizing Signs of Lithium Overdose
The signs of lithium toxicity can be subtle and often mimic symptoms of the flu or gastroenteritis, making early diagnosis challenging. Symptoms are generally classified by severity, with mild signs appearing at slightly elevated serum levels and progressing as the concentration increases. The earliest signs of mild toxicity often include gastrointestinal distress, such as persistent nausea, vomiting, and diarrhea.
Neurologically, mild toxicity can manifest as a fine tremor in the hands and a generalized feeling of fatigue or lethargy. These early signs should prompt an immediate medical evaluation, as the person’s condition can quickly worsen. When toxicity progresses to a moderate level, the neurological symptoms become much more pronounced.
A coarse tremor, which is more noticeable and involves larger muscle movements, often replaces the fine hand tremor. Moderate toxicity is also characterized by confusion, giddiness, and a lack of coordination, medically known as ataxia. The person may exhibit slurred speech and hyperreflexia, an exaggerated response of the deep tendon reflexes.
Severe lithium toxicity is a medical emergency that indicates very high levels of the drug in the body. Symptoms in this stage include seizures, stupor, and a progression toward coma. Acute kidney injury can occur, which further impairs the body’s ability to clear the lithium, creating a dangerous cycle. In the most severe cases, the person may experience cardiovascular collapse, which can be fatal.
Immediate Medical Response and Treatment
If lithium toxicity is suspected, the immediate action is to stop the medication and seek emergency medical attention. Treatment is focused on stabilizing the person and quickly reducing the lithium concentration in the bloodstream. The first step involves aggressive supportive care, which includes administering intravenous (IV) fluids, typically normal saline, to combat dehydration and restore the kidney’s ability to excrete the drug.
The medical team will continuously monitor the person’s cardiac rhythm and vital signs, as lithium can affect the heart. For an acute overdose, methods of gastrointestinal decontamination may be attempted if the person presents within the first hour of ingestion. This may involve gastric lavage or whole bowel irrigation, though activated charcoal is not effective because it does not bind to lithium.
The definitive treatment for severe lithium poisoning is hemodialysis, a process that rapidly cleanses the blood outside the body. Lithium is highly dialyzable, making this the most effective method to quickly remove the drug from circulation. Hemodialysis is typically reserved for cases where the lithium level is extremely high, the person is exhibiting severe neurological symptoms, or kidney function is significantly compromised.
Serial blood tests are performed regularly to track the lithium level and monitor kidney function until the concentration falls below the toxic threshold. Even after the blood level has normalized, medical monitoring is often continued, as lithium can move from the tissues back into the bloodstream, causing a “rebound” in the serum concentration.