The nurse has administered vasopressin to a client with diabetes insipidus. What finding should indicate the drug is effective?

A. Decreased serum potassium: Vasopressin does not significantly affect potassium levels. Changes in serum potassium are not used to evaluate the drug’s effectiveness in managing diabetes insipidus. B. Increased urine serum osmolality: Diabetes insipidus causes excessive dilute urine due to insufficient antidiuretic hormone activity. Effective vasopressin administration promotes water reabsorption in the kidneys, concentrating the urine and increasing urine osmolality, which indicates therapeutic success. C. Decreased blood pressure: Vasopressin can raise blood pressure through vasoconstriction, but a decrease in blood pressure would not indicate effectiveness in treating diabetes insipidus and may signal an adverse response or other condition. D. Increased heart rate: Heart rate changes are not a reliable indicator of vasopressin effectiveness for diabetes insipidus. Therapeutic monitoring focuses on urine output and concentration rather than cardiovascular parameters.