What are the effects of a lithium overdose?

Effects of Lithium Overdose

Lithium overdose is potentially lethal and primarily causes neurological toxicity, with cardiac complications occurring less frequently but carrying significant risk, especially in chronic toxicity cases. 1, 2

Types of Lithium Overdose

Three distinct patterns of lithium poisoning exist, each with different clinical implications:

1. Acute overdose: Single large ingestion in a person not on lithium therapy
2. Acute-on-chronic overdose: Large ingestion by a person already on lithium therapy
3. Chronic overdose: Most common type (56.2% of cases), usually unintentional, occurs when lithium intake exceeds elimination 3, 2

Neurological Effects

Neurological manifestations are dose-dependent and typically present as:

• Early signs (serum levels below 1.5 mEq/L):

  • Fine hand tremor
  • Drowsiness
  • Muscular weakness
  • Lack of coordination 1

• Moderate toxicity (serum levels 1.5-2.5 mEq/L):

  • Confusion
  • Giddiness
  • Ataxia
  • Blurred vision
  • Tinnitus 1, 2

• Severe toxicity (serum levels above 3 mEq/L):

  • Seizures
  • Coma
  • Stupor
  • Blackout spells
  • Incontinence
  • Acute dystonia 1, 4

Cardiovascular Effects

Cardiac complications occur in approximately 5.7% of hospitalized lithium overdose cases and include:

• Bradycardia (most common cardiac effect)
• Cardiac arrhythmias
• Hypotension
• Peripheral circulatory collapse
• Sinus node dysfunction with severe bradycardia (may cause syncope)
• Cardiovascular interventions are typically only required in chronic lithium toxicity cases 1, 3

Gastrointestinal Effects

• Nausea and vomiting (early warning signs)
• Diarrhea
• Anorexia
• Abdominal pain 1, 5

Renal Effects

• Polyuria and polydipsia (due to nephrogenic diabetes insipidus)
• Reduced urinary concentrating capacity
• Albuminuria
• Oliguria
• Glycosuria
• Progressive renal insufficiency (rare but potentially fatal complication) 1, 5, 4

Risk Factors for Severe Toxicity

Patients most likely to develop severe lithium toxicity have:

• Nephrogenic diabetes insipidus (strongest risk factor)
• Age over 50 years
• Thyroid dysfunction
• Impaired renal function
• Concomitant medications that impair lithium clearance 4

Management of Lithium Overdose

1. Immediate assessment:

   • Obtain serum lithium levels promptly and repeatedly
   • Monitor vital signs and neurological status

2. Supportive care:

   • Airway management and respiratory support if needed
   • IV fluid administration
   • Correction of electrolyte abnormalities

3. Enhanced elimination:

   • Hemodialysis is the treatment of choice for severe cases
   • Approximately 13.8% of hospitalized lithium overdose patients require hemodialysis 3, 2

4. Specific considerations:

   • Standard resuscitative measures should take priority over specific antidotes 6
   • After return of spontaneous breathing, patients should be observed in a healthcare setting until risk of recurrent toxicity is low 6

Prognosis

• Mortality rate is relatively low (0.8% in hospitalized cases)
• Chronic lithium poisoning may require prolonged hospitalization
• Persistent neurological deficits, particularly cerebellar damage, can occur
• Most patients recover without sequelae with appropriate treatment 3, 2, 7

Special Considerations

• Lithium has a narrow therapeutic index requiring careful monitoring
• Lithium toxicity is primarily iatrogenic and often preventable
• Patients with bipolar disorder should receive careful third-person supervision of lithium prescriptions as overdoses may be lethal 6, 4