Abstract

Lithium has been used increasingly for the prevention of episodes of affective disorder, both manic and depressive. It has also been advocated in the management of other psychiatric conditions such as schizophrenia, alcoholism and personality disorder. However, it has a low therapeutic index. In particular, it induces polyuria and polydipsia¹ which may be transient, recurrent or persistent. They are symptoms of nephrogenic diabetes insipidus,^{2 3} and are particularly prevalent in patients receiving additional psychotropic drugs.⁴ Between 5 and 30% of patients taking lithium suffer from polyuria, depending on dosage, dosage interval and total amount of lithium ingested; it may occur even after short-term treatment. The mechanism is that lithium inhibits the effect of antidiuretic hormone (ADH) on the kidney and so inhibits the ability of the kidney to concentrate urine.