Adverse effects

Adverse effects are not uncommon even if blood levels are carefully controlled, and patients must be supervised.

Common side effects within the therapeutic range include hand tremor, muscular weakness, nausea, polydipsia, and polyuria. These are not usually dangerous, but may indicate the beginning of the toxic syndrome. Tremor is very common. Thyroid enlargement, hypothyroidism, ECG changes, a diabetes insipidus-like syndrome and depletion of calcium from bone may also take place. The patient may complain of a metallic taste in the mouth due to lithium treatment. Skin rashes may occur.

The toxic syndrome occurs at levels above 1.4 mmol/l, and involves diarrhoea, vomiting, ataxia, nystagmus, dysarthria, confusion, epileptic seizures, which may lead to coma with hypereflexia and increased muscle tone - and in a few patients to irreversible neurological damage. If this syndrome occurs then the lithium salts should be discontinued, the fluid and electrolyte balance corrected, forced diuresis or dialysis, and symptomatic and supportive measures given, e.g. for seizures (1).

Note that there are certain circumstances where the patient is particulary at risk of developing a toxic reaction, which include:

• impaired renal function
• dehydration, for example due to diarrhoea and vomiting, or increased perspiration when visiting a hot climate. If the patient becomes dehydrated lithium treatment should be stopped.

The most important drug interaction of lithium is with sodium depleting drugs especially thiazides where significant lithium toxicity may occur. Other drugs which reduce lithium excretion include ACE inhibitors and NSAIDs (1).

Reference:

• Drug and Therapeutics Bulletin (1999), 37 (3), 22-24.