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:
- Endocrinological
- Thyroid dysfunction (both hypo and hyperthyroidism)
- Hyperglycaemia
- Hyperparathyroidism
- Hypercalcaemia
- Neurological
- Tremor
- Gastrointestinal
- Nausea/vomiting
- Anorexia
- Diarrheoa
- Excessive salivation
- Renal
- Nephrogenic diabetes insipidus (20 to 70%)
- Chronic renal failure
- Proteinuria
- Other
- Alopecia
- Metallic taste
- Leucocytosis
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
Management
- 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
References
BNF. Lithium. Accessed 22/5/12 at http://www.bnf.org/bnf/index.htm
Delva, N. and Hawken, E. Preventing lithium intoxication. Guide for physicians. Can Fam Physician. 2001; 47: 1595-1600.
MHRA. Lithium overdose. Accessed 22/5/12 at http://www.mhra.gov.uk/Howweregulate/Medicines/Licensingofmedicines/Informationforlicenceapplicants/Guidance/OverdosesectionsofSPCs/Genericoverdosesections/Lithium/index.htm
Sood, M. and Richardson, R. Negative anion gap and elevated osmolar gap due to lithium overdose. CMAJ. 2007; 176(7): 921-923.
BNF. Lithium. Accessed 22/5/12 at http://www.bnf.org/bnf/index.htm
Delva, N. and Hawken, E. Preventing lithium intoxication. Guide for physicians. Can Fam Physician. 2001; 47: 1595-1600.
MHRA. Lithium overdose. Accessed 22/5/12 at http://www.mhra.gov.uk/Howweregulate/Medicines/Licensingofmedicines/Informationforlicenceapplicants/Guidance/OverdosesectionsofSPCs/Genericoverdosesections/Lithium/index.htm
Sood, M. and Richardson, R. Negative anion gap and elevated osmolar gap due to lithium overdose. CMAJ. 2007; 176(7): 921-923.
