Lithium salts

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Lithium salts are used for their mood-regulating action in the treatment of manic illness and in the prevention of manic and depressive illnesses. Lithium treatment quietens the overactive euphoric patients. The decision to give prophylactic treatment usually requires specialist advice. It must be based on careful consideration of the likelihood of recurrence in the individual patient, and the benefit weighed against the risks. Lithium treatment is unsuitable for children.

Treatment should be discontinued only if relief from affective illness is absent or insignificant. In the initial stages supplementary treatment with antipsychotic drugs is usually required because it may take a few days for lithium to exert its effect. High doses of haloperidol, fluphenazine, or flupenthixol may be hazardous when used with lithium; irreversible toxic encephalopathy has been reported.

Lithium salts have a narrow therapeutic/toxic ratio and should therefore not be prescribed unless facilities for monitoring plasma concentrations are available. Patients should be carefully selected. Doses are adjusted to achieve plasma concentrations of 0.6 to 1.2mmol Li+/litre (lower end of the range for maintenance therapy and elderly patients) on samples taken 12 hours after the preceding dose. Overdosage. usually with plasma concentrations over 1.5mmol Li+/litre, may be fatal and toxic effects include tremor, ataxia, dysarthria, nystagmus, renal impairment, and convulsions. If these potentially hazardous signs occur, treatment should be stopped, plasma lithium concentrations redetermined, and steps taken to reverse lithium toxicity.

Lithium toxicity is made worse by sodium depletion. Concurrent use of diuretics that inhibit the uptake of sodium by the distal tubule (e.g. thiazides) is hazardous and should be avoided. In mild cases withdrawal of lithium and administration of generous amounts of sodium and fluid will reverse the toxicity. Plasma concentrations in excess of 2.5 mmol Li+/litre are usually associated with serious toxicity requiring emergency treatment. When toxic concentrations are reached there may be a delay of 1 or 2 days before maximum toxicity occurs.

In long-term use, therapeutic concentrations of lithium have been thought to cause histological and functional changes in the kidney. The significance of such changes is not clear but is of sufficient concern to discourage long-term use of lithium unless it is definitely indicated. Patients should therefore be maintained on lithium treatment after 3-5 years only if, on assessment, benefit persists. Conventional and sustained-release tablets are available but it should be noted that different preparations vary widely in bioavailability and a change in the formulation used requires the same precautions as initiation of treatment. There seem few if any reasons for preferring one or other of the simple salts of lithium; the carbonate has been the more widely used but the citrateis also available.