What is lithium toxicity

Lithium is a prescription medicine used to treat bipolar disorder. Lithium is a medicine with a narrow range of safety. Significant poisoning can result when the amount of lithium taken is more than this range. Acute lithium toxicity occurs when you swallow too much of a lithium prescription at one time.
Chronic lithium toxicity occurs when you slowly take a little too much lithium prescription every day for a while. This is actually quite easy to do, because dehydration, other medicines, and other conditions can easily affect how your body handles lithium. These factors can make the lithium build up to harmful levels in your body.

Acute on chronic lithium toxicity occurs when you normally take lithium every day for bipolar disorder, but one day you take an extra amount. This can be as little as a couple of pills or as much as a whole bottle.

Lithium toxicity can be classified into three major categories ¹:

1. Acute overdose in a lithium-naive patient.
2. Acute overdose in a patient on chronic therapy (acute-on-chronic).
3. Chronic over-medication or drug accumulation (associated with the most serious toxicity).

Lithium levels are monitored on a regular basis because blood levels must be maintained within a narrow therapeutic range. Too little and the medication will not be effective; too much and symptoms associated with lithium toxicity may develop.

Lithium is classified as pregnancy category D which means that there is positive evidence of human fetal risk. Therefore, a proper contraceptive method should be used during treatment with lithium.

Lithium toxicokinetics

• Different types of lithium formulations are present including sustained-release preparations.
• Lithium is neither metabolized nor protein bound, thus its bioavailability usually is close to 100%. Moreover, lithium absorption is rapid.
• Serum lithium levels reflect only the extracellular lithium concentration. However, lithium exerts its effects once it has moved to its intracellular compartment. This phenomenon illustrates the reason why patients with significantly elevated serum levels might be asymptomatic.
• Lithium is more susceptible to accumulation in liver, bone, muscle, or thyroid with brain and kidney showing the highest levels.
• The kidneys are responsible for 95% of lithium excretion, and the rest is removed through sweat and feces. The kidneys treat lithium and sodium similarly which is the reason sodium depletion can significantly elevate lithium reabsorption.
• Volume depletion from diuretics, dehydration, febrile illness, or gastrointestinal loss can lead to elevated lithium levels in the serum.
• The serum elimination half-life of lithium can vary from 12 to 27 hours. In patients with chronic intoxication, the half-life can be prolonged up to 48 hours.
  The renal clearance of lithium is usually 10 to 40 mL/ min. However, the clearance may be decreased to 15 mL/min, and the elimination half-life can be as long as 58 hours in elder patients.
• Lithium freely crosses the placenta and is also excreted in breast milk. It is labeled as pregnancy class D and has been implicated in the increased risk of congenital cardiac defects, particularly the Ebstein anomaly. Breastfeeding infants of mothers taking lithium have been reported to have signs of cyanosis, hypotonia, and lethargy.

Lithium toxicity causes

Too much lithium can cause lithium toxicity. Factors increasing lithium concentration in the body include excessive intake and impaired excretion.

Lithium toxicity is common because it is commonly prescribed as maintenance therapy for patients with bipolar disorder, a population with relatively high risk for overdose as a result of suicidal attempts. Moreover, it has a narrow therapeutic index which exposes the patients on maintenance therapy to toxicity.

Excessive Intake

Suicidal intent or accidental ingestion of excessive amount of lithium tablets result in acute or acute-on-chronic overdose settings. Moreover, excessive intake might arise from dose modifications for the patient chronically administering lithium.

Impaired Excretion

Several factors might lead to impairment in lithium secretion. Sodium and volume depletion due to any conditions like vomiting, diarrhea, febrile illness, renal insufficiency, excessive exercise, water restriction, excessive sweating, low sodium diet, and congestive heart failure may enhance lithium reabsorption in the kidneys. Furthermore, drugs reducing glomerular filtration rate might inflict chronic toxicity.

• Chronic therapy with lithium can precipitate nephrogenic diabetes insipidus, which might elicit a cascade of symptoms and signs of lithium toxicity. This can be attributed to the diminished urinary concentrating capacity of the kidneys.
• A vicious cycle of lithium toxicity might result from the concomitant existence of intercurrent illness with the reduced kidney concentrating capacity precipitated by lithium. For example, reduced clearance and excretion of lithium in case of sodium and volume depletion will result in increased lithium concentration in the serum, which in turn continues to affect the kidneys’ ability to concentrate urine negatively.

Lithium toxicity signs and symptoms

Symptoms of the three types of lithium toxicity are described below.

Acute lithium toxicity

Common symptoms of taking too much lithium at one time include:

• Diarrhea
• Dizziness
• Nausea
• Stomach pains
• Vomiting
• Weakness

Depending on how much lithium was taken, a person may also have some of the following nervous system symptoms:

• Coma (decreased level of consciousness, lack of responsiveness)
• Hand tremors
• Lack of coordination of arms and legs
• Muscle twitches
• Seizures
• Slurred speech
• Uncontrollable eye movement

Heart problems may occur in rare cases.

Neurologic effects

Symptoms of intoxication include coarse tremor, hyperreflexia, nystagmus, and ataxia. Patients often show varying consciousness levels, ranging from mild confusion to delirium. Although the neurological symptoms are mostly reversible, some reports indicate that symptoms might persist for 12 months never resolve.

Renal toxicity

Renal toxicity is more common in patients on chronic lithium treatment. Toxicity includes impaired urinary concentrating ability, nephrogenic diabetes insipidus (the most common cause of drug-induced nephrogenic diabetes insipidus), sodium-losing nephritis, nephrotic syndrome along with other manifestations is prescribed.

Cardiovascular effects

These are usually mild and non-specific. Almost all patients treated with lithium will develop T wave flattening. Sinus node dysfunction is the most common reported conduction defect followed by QT prolongation, intraventricular conduction defects, and U waves. These findings are reversible.

Gastrointestinal effects

Symptoms typically occur within 1 hour of ingestion and are more common in the acute overdose setting.

Endocrine effects

Lithium administration leads to the inhibition of thyroid hormone synthesis and subsequent release, resulting in hypothyroidism. Hyperthyroidism is less commonly manifested, which can mask symptoms of lithium toxicity and boost its toxicity by prompting cellular unresponsiveness and altered renal tubular handling of lithium.

Chronic lithium toxicity

There will likely not be any stomach or intestinal symptoms. Symptoms that can occur include:

• Increased reflexes
• Slurred speech
• Uncontrolled shaking (tremors)

In severe cases of chronic lithium toxicity, there may also be nervous system and kidney problems, such as:

• Kidney failure
• Memory problems
• Movement disorders
• Problems keeping salts in your body
• Psychosis (disturbed thought processes, unpredictable behavior)

Acute on chronic lithium toxicity

There will often be some stomach or intestinal symptoms and many of the severe nervous system symptoms listed above.

Lithium toxicity complications

Intoxication degree is of utmost importance for understanding lithium toxicity diagnosis and management.

The severity of lithium toxicity is often divided into the following three grades: mild, moderate, and severe.

• Mild symptoms: nausea, vomiting, lethargy, tremor, and fatigue (Serum lithium concentration between 1.5-2.5 mEq/L).
• Moderate intoxication: confusion, agitation, delirium, tachycardia, and hypertonia (serum lithium concentration between 2.5-3.5 mEq/L).
• Severe intoxication: Coma, seizures, hyperthermia, and hypotension (serum lithium concentration (less than 3.5 mEq/L).

Lithium toxicity diagnosis

Initially, the investigation should include cardiac monitoring, electrocardiogram (ECG), assessment of oxygenation and monitoring of urine output, serum electrolytes, calcium, renal function, glucose, serum lithium level, and thyroid-stimulating hormone. Moreover, both therapeutic lithium usage and intoxication can be accompanied by leukocytosis. Furthermore, interference by the carbonate anion after lithium carbonate acute ingestion in the calculation of anion gap might lead to a low anion gap.

• Patients are susceptible to renal insufficiency with elevated blood urea nitrogen and creatinine in case of chronic intoxication.
• If the initial diagnosis is unclear, brain imaging may be required. Though some formulations of lithium may be radiopaque, radiography is not dependable for ruling out ingestion.
• Lithium serum levels normally range from approximately 0.6 to 1.2 mEq/L. Measurement of the serum levels should be carried out at least 6 to 12 hours after the last therapeutic dose to avoid misinterpretation of pre-distributional levels.

These levels can be misrepresentative owing to lithium’s low therapeutic index and because its levels poorly correlate with the level of toxicity. After an acute overdose with lithium levels reaching 10.6 mEq/L (10.6 mmol/L), no neurologic toxicity has been reported because of the multi-compartment kinetics of the drug. Furthermore, because serum levels do not accurately reflect the intracellular concentration or toxicity of the drug, a normal level does not exclude toxicity.

Of note, lithium heparin is used as an anticoagulant in some specimen tubes which can falsely increase results of serum lithium.

Lithium toxicity treatment

Supportive Measures

• Essential initial treatment of lithium toxicity includes managing the Mairway, assessing vital signs, and monitoring cardiac activity continuously.
• Administering fluids, as well as other general emergency treatment measures including dextrose and naloxone when needed, necessitates placement of peripheral intravenous lines.
• Treat hyperthermia or hypothermia appropriately.
• If seizures occur, initiate regular measures including benzodiazepines and barbiturates.
• Electrocardiographic findings such as flattened or inverse T waves and mild QT prolongation do not usually require treatment; however, treat severe arrhythmias with usual measures, including magnesium for marked QT prolongation or torsades de pointes.
• Fluid therapy starts with isotonic saline. It is an essential step in treating lithium intoxication that aims to preserve GFR and urine output to reduce sustained lithium reabsorption.

Decontamination

• In-vitro studies showed that lithium does not adhere effectively to activated charcoal; however, if co-ingestants are unknown, charcoal should be administered.
• Gastric lavage should be considered, particularly in the case of regular-release preparations and patients presenting early to the emergency department. On the other hand, in case of sustained-release preparations, administration, or massive ingestion of regular-release products, whole-bowel irrigation should also be considered.

Elimination

• The most appropriate method of lithium removal is hemodialysis, particularly if the patient demonstrates signs and symptoms of severe lithium poisoning or is having a renal failure due to its small volume of distribution and marginal protein binding.
• Peritoneal dialysis should not replace hemodialysis; however, if the hemodialysis facilities are not available (e.g., in remote areas), peritoneal dialysis can be initiated.

Disposition

• All patients with toxicity signs and symptoms, even those with normal serum lithium levels, should be admitted for monitoring in the hospital.
• In case of moderate or severe symptoms, the patient has to be admitted to an intensive care unit.
• Serial levels of lithium in the serum should be obtained every 6 hours in case of asymptomatic patients after an acute ingestion. This should be continued until a descending drift has been established.
• Patients should not be discharged until they are asymptomatic and have a serum lithium level less than 1.5 mEq/L.

Lithium toxicity prognosis

If someone has acute lithium toxicity, how well they do depends on how much lithium they took and how quickly they get help. In some cases, lithium toxicity can lead to coma, brain damage, or even death. Moreover, lithium can induce serotonin syndrome, a potentially fatal and life-threatening condition. The use of serotonergic drugs or drugs inhibiting serotonin metabolism concomitantly with lithium will increase the risk of lithium precipitating serotonin syndrome.

Lithium toxicity signs are obvious and can be identified and managed easily. People who do not develop nervous system symptoms usually do not have long-term complications. If serious nervous system symptoms occur, these problems may be permanent.

Chronic toxicity is sometimes hard to diagnose at first. This delay can lead to long-term problems. If dialysis is done quickly, the person may feel much better. But symptoms such as memory and mood problems may be permanent.

Acute on chronic overdose often has the worst outlook. Nervous system symptoms may not go away, even after many dialysis treatments.

1. Hedya SA, Swoboda HD. Lithium Toxicity. [Updated 2018 Dec 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499992[↩]