Mannitol: Dose for Intraocular Pressure

• Availability: Mannitol 10% (10g/100ml) & Mannitol 20% (20g/100ml)

Description	Reduces elevated IOP when pressure cannot be lowered by other means. Initially assess for adequate renal function in adults by administering a test dose of 200 mg/kg IV over 3-5 min. Should produce a urine flow of at least 30-50 mL/h of urine over 2-3 h. In children, assess for adequate renal function by administering a test dose of 200 mg/kg IV over 3-5 min. Should produce a urine flow of at least 1 mL/h over 1-3 h.
Adult Dose	1.5-2 g/kg IV as 20% solution (7.5-10 mL/kg) or as 15% solution (10-13 mL/kg) over a period as short as 30 min
Pediatric Dose	Not established
Contraindications	Documented hypersensitivity; anuria, severe pulmonary congestion, progressive renal damage, severe dehydration, active intracranial bleeding, and progressive heart failure
Interactions	May decrease serum lithium levels
Pregnancy	C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions	Carefully evaluate cardiovascular status before rapid administration of mannitol since a sudden increase in extracellular fluid may lead to fulminating CHF; avoid pseudoagglutination, when blood given simultaneously, add at least 20 mEq of sodium chloride to each liter of mannitol solution; do not give electrolyte-free mannitol solutions with blood

General

• An intravenous dose of 100–200 ml of 20% mannitol reduces normal IOP by an average of 8–9 mmHg
• The decrease was 4 and 8 mmHg at 15 min for 100 and 200 ml, respectively.
• The peak occurs at 40 min, and the IOP returns to baseline within 2 hr  
• Mannito causes a disturbing osmotic diuresis in almost one-third of patients after a dose of 200 ml

Reduction of intraocular pressure

• IV: 0.25 to 2 g/kg administered over 30 to 60 minutes 1 to 1.5 hours prior to surgery (LexiComp)
• IV: 1.5-2 g/kg infused over 30-60 minutes (Medscape and Manufacturer)

Reduction of intraocular pressure (traumatic hyphema):

• IV: 1.5 g/kg administered over 45 minutes twice daily for IOP >35 mm Hg; may administer every 8 hours in patients with extremely high pressure (Crouch, 1999)

Usage in Geriatrics

• As for adults, the dosage depends on the weight, clinical and biological condition of the patient and concomitant therapy.
• The general dose range is the same as for adults (50 to 200 g in 24-hour period), with a dosage limit of 50 g on any one occasion.
• Since incipient renal insufficiency may be present, caution should be used when reviewing patient’s status prior to dose selection

Overdosage

• Larger doses than recommended may result in increased electrolyte excretion, particularly sodium, chloride, and potassium.
• Sodium depletion can result in orthostatic tachycardia and/or hypotension and decreased central venous pressure.
• Chloride metabolism closely follows that of sodium. Potassium deficit can impair neuromuscular function and cause intestinal dilatation and ileus.
• Mannitol may cause pulmonary edema or water intoxication if urine flow is inadequate

Rational for lower dose

• Mauger et al. from Ohio State showed that a modest dose of only 12.5 g Mannitol (62.5 mL of 20%) dropped IOP over half an hour, and lasted for 2 hours.
• A cautionary case report from Tsai & Shu describes mannitol given intra-operatively to a 62 year old for intraocular pressure effects, that lead to hypertonic hyponatremic renal failure seven days later.  
• In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal or cardiac function, and of concomitant disease or other drug therapy.

References

1. Intraocular pressure, anterior chamber depth and axial length following intravenous mannitol. J Ocul Pharmacol Ther. 2000 Dec;16(6):591-4.
2. Mannitol-induced acute renal failure. Clin Nephrol. 2010 Jul;74(1):70-3.
3. Keeffe M & Nabil M (1983): The use of mannitol in intraocular surgery. Ophthalmic Surg 14: 55–56.
4. Osmitrol Intravenous Infusion (Mannitol), Product Information Leaflet
5. http://www.drugs.com/pro/mannitol-injection.html