Lithium is a drug with a narrow therapeutic window which is used predominantly in the treatment of bipolar disorder

It is predominantly renally excreted. 

Peak plasma levels usually occur between 0.5 to 4 hours but can occur up to 72 hours in case of overdose; steady state is achieved in 6 days.

Side effects of lithium include:

Factors that predispose to lithium toxicity include 
  • Increasing age 
  • Anorexia 
  • Diarrhoea 
  • Vomiting 
  • Dehydration 
  • Hypertension 
  • Heart disease 
  • Renal impairment 
  • Hypothyroidism 
  • Drugs 
    • ACE inhibitors 
    • Diuretics 
    • NSAIDs 
    • Calcium channel blockers 
    • Neuroleptics 
    • Antiepileptics 

Symptoms of toxicity 
  • Mild toxicity 
    • Vomiting 
    • Diarrhoea 
    • Lethargy 
    • Tremor 
    • Drowsiness 
    • Muscle weakness 
    • Polyuria
    • Polydipsia 
  • Moderate toxicity 
    • Confusion 
    • Nystagmus 
    • Cerebellar signs 
  • Severe toxicity 
    • Altered state of consciousness 
    • Syncope 
    • Seizures 
    • Hyperreflexia 
    • Arrhythmias 

The most common manifestation of toxicity is altered mental state. 

Investigations if toxicity is suspected:
  • Lithium level – but note toxicity can occur within the therapeutic range
  • Full set of bloods
  • Calculate anion gap ( = Na – (Cl + HCO3) ) – look for a low anion gap 
  • Calculate osmolar gap (= plasma osmolality – ((2xNa) + plasma glucose + urea) ) – look for an elevated osmolar gap 

  • Manage airway as appropriate 
  • Gastric lavage if OD less than 1 hour previously 
  • ?whole bowel irrigation if large quantities of slow-release tablets swallowed
  • IV saline if volume depleted
  • haemodialysis 

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