A client with diabetes insipidus has been taking desmopressin. Which is the best indicator that the medication is ineffective? Laboratory Reference Ranges:Serum sodium: 135-145 mEq/L. Urine specific gravity: 1.005-1.030

Desmopressin is a synthetic analog of antidiuretic hormone (ADH/vasopressin) used to treat diabetes insipidus (DI). Its therapeutic effect is to increase water reabsorption in the renal collecting ducts, which reduces urine output and relieves excessive thirst (polydipsia). Continued excessive thirst and large urine output — the hallmark symptoms of diabetes insipidus — indicate that the medication has failed to produce its desired antidiuretic effect and is therefore ineffective. A serum sodium of 135 mEq/L is within the normal reference range of 135–145 mEq/L, suggesting adequate water balance and would actually indicate the drug is working. A urine specific gravity of 1.030 is at the upper limit of normal and reflects concentrated urine, also suggesting therapeutic effect rather than failure. Slight peripheral edema and weight gain can be signs of excessive desmopressin effect (overtreatment leading to water retention), not ineffectiveness. Students must focus on the core pathophysiology: in untreated or inadequately treated DI, patients produce large volumes of dilute urine and experience persistent thirst. Persistence of these symptoms while on desmopressin is the clearest indicator of treatment failure.