Sir.—Aggarwal et al,1 in the November 1986 issue of AJDC, reported the association of nephrogenic diabetes insipidus, hydrocephalus, and optic atrophy in a 15-week-old female infant. They based their assumption of antidiuretic hormone resistance on the failure to document urinary concentration after a subcutaneous injection of 5 U of vasopressin. Such an unphysiologically high dose of vasopressin is likely to cause vasoconstriction and failure to elicit urinary concentration, even in a healthy infant. The test did not negate the more likely coexistence of optic atrophy, hydrocephalus, and central diabetes insipidus.
For documentation of a vasopressin response in older children, it is preferable to inject desmopressin acetate (0.05 to 0.1 μg/Kg) subcutaneously. In infants, a total dose of 0.5 μg is well tolerated and causes antidiuresis for at least eight hours. During the period of drug-induced antidiuresis, fluid intake has to be reduced, and body weight should be