Milliosmoles Calculation in Pharmacy
The milliosmole (mOsmol) is the unit of measure for osmotic concentration. For nonelectrolytes, 1 millimole represents 1 mOsmol. However, for electrolytes, the total number of particles in a solution is determined by the number of particles produced in a solution and influenced by the degree of dissociation.
The ideal osmolar concentration can be calculated with the following equation:
mOsmol = [weight (g) ÷ mol. Wt.] ˟ number of species ˟ 1000
It can also be represented as mOsmol/L and gram/L:
mOsmol/L = [weight (g/L) ÷ mol. Wt.] ˟ number of species ˟ 1000
Calculation Example
1. What is the osmolarity of 0.9%w/v NaCl injection?
Here,
- 0.9% w/v= 0.9 g/ 100 mL = 9 g/L
- Molecular weight of NaCl = 58.5
mOsmol= [weight (g) ÷ mol. Wt.] ˟ number of species ˟ 1000 = (9 ÷ 58.5) × 2 ×1000 = 308 mOsmol = 0.308 Osmol
2. A solution contains 156 mg of K+ ions per 100 mL. How many mOsmoles are represented in a liter of the solution? Atomic weight of K+ =39
Here,
- 156 mg/100 mL = 0.156 g/ 100 mL= 1.56 g/L
- mOsmol/L = No. of moles x No. of species x 1000
- Number of moles= weight/ mol. wt. = 1.56/39= 0.04
mOsmol/L = 0.04 x 1 x 1000= 40 mOsmol/L.
3. A parenteral solution contains 5% dextrose. How many mOsmoles per liter are represented by this concentration?
Here,
- 5% = 5 g/100 mL = 50 g/ L
- Molecular weight (MW) of dextrose = 180
- Dextrose is non-electrolyte, so, number of species = 1
[weight (g/L) ÷ mol. Wt.] ˟ number of species ˟ 1000
mOsmol/L = (50 ÷ 180) × 1 × 1000 = 278 mOsmol/L.
Read also:
