Glycerol is also known as glycerin, which is available as a 99.5% anhydrous solution. Although a commercial product is unavailable, a 50% solution of glycerol can
Table 8.2 Dosage and Administration of Commonly Used Osmotic Drugs
Drug Solution Route Dose (g/kg)
Mannitol 20% (wt/vol) Intravenous 0.5-2
be prepared by most pharmacies, which use glycerol to formulate other medications. Glycerol is prepared as a 50% vol/vol (0.628g/mL) solution for oral administration and may be stored at room temperature. The usual dose is 1 to 1.5 g/kg, which is about 2 to 3mL/kg body weight (*4 to 6 ounces per individual). Flavoring and pouring the glycerol solution over ice improve palatability.
Isosorbide for oral administration is no longer available as a commercial product. Isosorbide is prepared as a 45% wt/vol solution in a flavored vehicle and is chemically stable at room temperature. The usual dose is 1 to 2 g/kg of body weight, which is equivalent to 1.5mL/lb body weight. Because the osmotic effect persists up to 5 or 6 hours, doses may be repeated two to four times per day during the short-term use of the drug.
The usual dose of mannitol for reduction of IOP is 0.5 to 2g/kg of body weight, given as an intravenous infusion of a 20% solution over a period of 30 to 60 minutes. Doses as low as 0.25 g/kg may be effective. A single low dose of 12.5 g lowered IOP in normal subjects.18 Alternative concentrations for ophthalmic use include 10%, 15%, and 25% mannitol. The dose may be lowered if the IOP is not too high or increased if there is pronounced intraocular inflammation. Less than the full dose may be administered by terminating the intravenous infusion when the desired effect on IOP is achieved. The solution is stored at room temperature, and higher concentrations may require slight warming for complete solution. Crystals may form at temperatures below room temperature. When mannitol concentrations of 20% or 25% are infused, the administration set should include a filter.
When an intravenous osmotic drug is required, mannitol is preferable to urea. Although urea is not commonly used, the dosage of intravenous urea is 2 to 7mL/kg of a 30% solution. The solution of urea is unstable and must be prepared just prior to intravenous administration.
Osmotic drugs in common clinical use are shown in table 8.2.
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