[Fluctuating hyponatremia following transsphenoidal surgery ‒ "The challenge of correcting without going too far"].

Introduction: sodium disorders following pituitary represent one of the most common complications. Differential diagnosis between syndrome of inappropriate antidiuretic hormone secretion (SIADH) and a triphasic response is critical to avoid overcorrection. Case report: we report a case of a 58-year-old male who underwent surgery for a pituitary macroadenoma and developed a triphasic response: initial polyuria, followed by transient SIADH. Due to a suboptimal response to fluid restriction and the risk of transitioning to a new polyuric phase, oral urea (30 g/day) was started. Gradual and safe sodium correction was achieved (128 to 132 mmol/l in 36 h), allowing early detection of the final shift back to diabetes insipidus without exceeding safety limits. Discussion: all in all, oral urea is an effective alternative for postoperative SIADH, providing more predictable and reversible osmotic control in scenarios of fluctuating natremia.