Pharmacokinetics:

After liquid lithium, peak concentrations occur after 30 minutes. With sustained release tablets absorption is variable starting after 30 minutes with peak concentrations after 4-5 hours. Half-life ranges from 8-45 hours (mean 24 hours)(Dollery 1999); this may be prolonged in overdose .

 

Pregnancy:

The use of lithium during the 1st trimester may be related to an increased incidence of congenital defects, particularly of the cardiovascular system (Briggs et al 1994). .

Lithium - features and management

Updated 5/2002

 

Clinical effects:

The onset of symptoms may be delayed for up to 24 hours especially in lithium naive patients.

Mild: Nausea, diarrhoea, blurred vision, polyuria, light headedness, fine resting tremor, muscular weakness and drowsiness.

Moderate: Increasing confusion, blackouts, fasciculation and increased deep tendon reflexes. Myoclonic twitches and jerks, choreoathetoid movements, urinary or faecal incontinence, increasing restlessness followed by stupor. Hypernatraemia.

Severe: Coma, convulsions, cardiac dysrhythmias including SA block, cerebellar signs, sinus and junctional bradycardia and first degree heart block. Hypotension or rarely hypertension, peripheral vascular collapse and renal failure.

 

Management:

1. Ensure a clear airway and adequate ventilation in patients who are unconscious.

2. In acute cases measure the lithium concentration at 6 hours and repeat 6-12 hourly. For acute on chronic or chronic accumulation measure the serum lithium concentration immediately and at 6 hours, then repeat 6-12 hourly. Do not use lithium-heparin tubes for the sample.

3. For acute or acute on chronic overdose of sustained-release preparations - slow-release tablets do not disintegrate in the stomach and most are too large to pass up a lavage tube. Therefore lavage may be of limited value. Whole bowel irrigation has been suggested for ingestion of more than 4 g by adults or definite ingestion of a significant amount by a child but there are no clinical trials to confirm its efficacy. Discuss with the National Poisons Information Service 0870 600 6266 (in Ireland NPIC (01) 809 2566).

Consider gastric lavage for non-sustained-release preparations if more than 4 g has been ingested by an adult within 1 hour or definite ingestion of a significant amount by a child.

Gut decontamination is not useful for chronic accumulation.

NOTE: Activated charcoal does not adsorb lithium.

4. All patients should be observed for a minimum of 24 hours.

5. Ensure adequate hydration and correct any electrolyte imbalance in patients with mild symptoms.

6. Forced diuresis and thiazide diuretics are contraindicated.

7. Monitor the ECG in symptomatic patients.

8. Correct hypotension by raising the foot of the bed or in severe cases by expanding the intravascular volume. In extreme cases dopamine or dobutamine may be required.

9. Control convulsions with intravenous diazepam (0.1-0.3 mg/kg body weight) if they are isolated. If they are more frequent it may be necessary to intubate, paralyse and ventilate the patient.

10. Haemodialysis is the treatment of choice for severe poisoning and should be considered in all patients with neurological features. It is the most efficient method of lowering lithium concentrations rapidly but substantial rebound increases can be expected when dialysis is stopped, and prolonged, or repeated treatments may be required. It should be considered also in acute overdose if the lithium concentration is >7.5 mmol/L. In cases of acute on chronic overdose or in cases of chronic lithium toxicity if the lithium concentration is >4.0 mmol/L. Discuss with the National Poisons Information Service 0870 600 6266 (in Ireland NPIC (01) 809 2566).

NB Clinical improvement generally takes longer than reduction of serum lithium concentrations regardless of the method used.

11. Repeat measurements of lithium concentration, performed routinely, are helpful in timing the appropriate re-institution of chronic therapy following an episode of toxicity. The usual target range is approximately 0.4 - 1.0 mmol/L12 hours post dose.