• Prophylaxis of recurrent episodes of affective disorder, when these are sufficiently frequent or disabling to justify long-term continuous drug treatment. In the past, lithium has been used mainly in bipolar disorder, being effective in reducing both frequency and severity of episodes. Lithium is now increasingly used in prophylaxis of recurrent unipolar depression also.

• Adjunctive treatment of episodes of mania and depression.

• Schizo-affective disorder. Administration

Although any of lithium's soluble salts could potentially be used, only the carbonate (tablets) and citrate (liquid) are marketed. The most practical formulations are modified release tablets, allowing once daily dosage. Because bioavailability varies greatly between different brands, the prescriber should specify the brand.

Therapeutic effect is related to serum lithium level. The therapeutic range is 0.4-1.0 mmol/l. Levels of 0.8-1.0 mmol/l were traditionally recommended for prophylaxis, but these would now be regarded as higher than necessary for satisfactory maintenance of the majority of patients. The aim is to keep patients well on the minimum dose, which is achieved by frequent monitoring of the clinical state, and by regular blood tests.

Lithium has a narrow therapeutic margin, and there is individual variation in the dosage needed to produce a given serum level, so regular measurements are required. Blood for serum lithium should be taken 8 hours after the last dose. This usually means first thing in the morning after the regular nighttime dose. Blood tests may be weekly for, say, the first 4 weeks of therapy, and eventually patients can be maintained satisfactorily on a blood test every year. The blood test should include thyroid function tests and urea and electrolytes, to make sure that the thyroid and kidneys are not being affected.

Patients should carry a lithium card and be advised to maintain good fluid intake, without huge fluctuations in the amount of salt they consume. If they become unwell, they should seek medical advice and inform the doctor that they are taking lithium.

Extra tests should be performed in the event of a change in the preparation or in dosage, if symptoms suggesting lithium toxicity develop, if intercurrent illness develops, or at prescription of additional drugs, which may interact, especially diuretics.

If a patient has remained free of depression or mania for some years, it is reasonable to try gradual withdrawal of lithium, as the illness may have undergone natural remission.

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