Mannitol is an osmotic diuretic. It is used for Increased intracranial or intraocular tension (acute congestive glaucoma, head injury, stroke, etc.): by osmotic action, it encourages the movement of water from brain parenchyma, CSF and aqueous humor; The dose is 1-1.5 g/kg is infused over 1 hour as 20% solution to transiently raise plasma osmolarity. It is also used before and after ocular /brain surgery to prevent the acute rise in intraocular/intracranial pressure. osmotic diuretics are excreted unchanged in the urine ( Essentials of Medical Pharmacology, K.D Tripathi,6th edition, page 572 ) eding