Diabetes Insipidus
A condition causing production of large volumes of dilute urine and excessive thirst due to insufficient vasopressin (central DI) or kidney resistance to vasopressin (nephrogenic DI). Desmopressin is the primary treatment for central DI, available as nasal spray, oral tablet, and injection.
Technical Context
Central DI causes: idiopathic (~30%), post-neurosurgical (pituitary/hypothalamic surgery — may be transient or permanent), head trauma, pituitary tumours, infiltrative diseases (sarcoidosis, histiocytosis), autoimmune (anti-vasopressin neuron antibodies), and genetic (rarely, mutations in AVP gene). Diagnosis: water deprivation test (restrict fluids → measure urine osmolality — failure to concentrate urine >300 mOsm/kg; then administer desmopressin → if urine concentrates >50% increase, central DI confirmed; if no response, nephrogenic DI). Desmopressin therapy: intranasal (10-40μg daily in 1-3 doses, bioavailability ~3-5%), oral tablet (100-800μg daily, bioavailability ~0.1%), oral lyophilisate/melt (60-360μg daily, sublingual absorption), and parenteral (1-4μg daily SC/IV — for acute or perioperative use). Dose titration: target adequate fluid balance (urine output 1.5-2.5 L/day) while avoiding hyponatraemia from excessive water retention. Hyponatraemia is the primary safety concern — patients must allow breakthrough polyuria periodically to prevent water intoxication.