Diuretics after transurethral prostatectomy: a double-blind controlled trial comparing frusemide and mannitol.

Mannitol and frusemide were compared in a randomized, controlled, double-blind trial for their effects in promoting diuresis after prostatectomy and on indices of water intoxication. The drugs had comparable diuretic effects. Sodium loss was greater with frusemide, contributing to sodium depletion after operation. Administration of frusemide was associated with more frequent need for i.v. volume expansion after operation. Plasma osmolality was greater with mannitol (289 (SD 4.2 mosmol kg-1 at 1 h after operation and 285 (5.3) mosmol kg-1 at 4 h after operation) than with frusemide (282 (7.1) mosmol kg-1 and 279 (6.7) mosmol kg-1, respectively) (P less than 0.05). Plasma concentration of sodium was significantly greater with mannitol (136.9 (3.1) mmol litre-1) than with frusemide (134.4 (2.8) mmol litre-1) only on the morning after surgery (P less than 0.05). Mannitol is an effective alternative to frusemide in inducing diuresis after prostatectomy, and may protect against water intoxication.