## Saturday, December 5, 2015

### Dosage Calculation - Mass/Liquid For Liquid Questions

Source Website: http://www.dosagehelp.com/liquid.html
By DosageHelp.com

Mass/Liquid For Liquid Questions
Given an amount of mass per liquid, how much liquid do you require?

Formula:

$\overline{)\frac{{\mathbf{Ordered}}}{{\mathbf{Have}}}x{\mathbf{Volume Per Have}}={\mathbf{Y\left(Liquid required\right)}}}$

Example: Phenytoin (Dilantin), 0.1 g PO, is ordered to be given through a nasogastric tube. Phenytoin is available as 30 mg / 5 mL. How much would the nurse administer?
$\frac{{\mathbf{Ordered}}}{{\mathbf{Have}}}x{\mathbf{Volume Per Have}}={\mathbf{Y\left(Liquid required\right)}}$
Convert 0.1 g to mg.
mcg ← mg ← g ← kg    ( x by 1,000 )
0.1 g x 1,000 = 100 mg

$\frac{{\mathbf{100 mg}}}{{\mathbf{30 mg}}}x{\mathbf{5 mL}}=\overline{){\mathbf{16.7 mL}}}$
Alternatively, 30 mg = 5 mL
Therefore 100 mg = 5/30 x 100 = 16.67 mL

Example: Ordered Lasix 40 mg IV push now. Available: 80 mg in 1 mL. How much will the nurse draw up?
$\frac{{\mathbf{Ordered}}}{{\mathbf{Have}}}x{\mathbf{Volume Per Have}}={\mathbf{Y\left(Liquid required\right)}}$
$\frac{{\mathbf{40 mg}}}{{\mathbf{80 mg}}}x{\mathbf{1 mL}}=\overline{){\mathbf{0.5 mL}}}$
Alternatively, 80 mg = 1 mL
Therefore 40 mg = 1/80 x 40 = 0.5 mL

Example: (From Ngee Ann Polytechnics Dosage Calculation Worksheet)
ORDER: Drug A 100,000 units P.O.
AVAILABLE: Drug A 1,000,000 units per 20 mL

${\mathbf{\text{GIVE:}}}\overline{)\phantom{\rule{30pt}{12pt}}}{\mathbf{\text{mL}}}$
$\frac{{\mathbf{Ordered}}}{{\mathbf{Have}}}x{\mathbf{Volume Per Have}}={\mathbf{Y\left(Liquid required\right)}}$
$\frac{{\mathbf{100,000 units}}}{{\mathbf{1,000,000 units}}}x{\mathbf{20 mL}}=\overline{){\mathbf{2 mL}}}$
Alternatively, 1,000,000 units = 20 mL
Therefore 100,000 units = 20/1,000,000 x 100,000 = 2 mL

Reference