RSPT 1213 – Basic Respiratory Care Pharmacology
Drug Calculations
Lecture Notes/Handout
I. Metric conversions – at times it will be required that conversions are
performed.
a. 1 mg = .001g
b. 1g = 1000mg
c. 1000 ml = 1L
d. Perform the following:
2500 g
1.35 kg
cc
35 mg
7.5 ml
mg
g
.19L
g
cc
II. Calculating with proportions
a. Convert to consistent unit of measure
b. Set up proportion
Original dose
Desired dose
=
per amount
Per amount
OR
Original dose: per amount :desired dose: per amount
 EXAMPLE: 0.5g is needed of a drug that comes in 250
mg/tablet
c. Drug in a solution
 EXAMPLE: 120 mg of Phenobarbital in 30 ml of
Phenobarbital elixir. How many ml of elixir is required to
deliver 15 mg?
 EXAMPLE: there is 0.2 mg/ml in glycopyrrolate. The order
requires 1.5 mg, how many ml is required?
d. Calculate with a dosing schedule – usually based on pt wt.
 Schedule = what should be given
 Prepared strength mixture (on hand)
 EXAMPLE: The dosing schedule for a patient receiving
albuterol syrup is 0.1 mg/kg. The syrup comes 2
mg/5ml. How much syrup is required for a 20 kg child?
 EXAMPLE: a dose of surfactant calls for 5cc/kg; the infant
weighs 1200g. How much surfactant will be delivered?
III. Percentages
a. Solution: composed of solute (med) dissolved in a solvent
(liquid)
b. Percentage strength solution: consists of active ingredient
(solute) contained in 100 parts of total preparation.
c. Types of % preparations
 Weight-Weight: g/100g ,mixture
 Weight-volume: g/100 ml mixture
 Volume-volume: ml/100ml mixture
IV. Solutions by Ration (solute-to-solvent)
a. Ratio is g/ml
 EXAMPLE: isoproterenol 1:200 solution
 EXAMPLE: Epinephrine 1:100 solution
V. Ratio by Simple parts
a. 1:8 is 1 part to 8 parts; or ¼ cc to 2cc
b. Doesn’t state actual amounts or specific units; 1:8 is not precise
c. Solution with pure active ingredient; (no dilution or 100%
strength)
Solute (g or cc)
% strength
=
(in decimals)
Total amount (solute & solvent)
OR
Amount solute
Amount of solute
=
Total amount
100 parts (g or cc)
 EXAMPLE: How many mg of active ingredient are there in
2 cc of 1:200 isoproterenol?
d. When active ingredient is already diluted (less than pure)
Desired %
(Dilute solute) x (% strength of solution)
=
strength
Total amount of solution
(in decimals)
 EXAMPLE: How much 20% mucomyst is needed to prepare
5cc of 10% mucomyst?
 EXAMPLE: How much 20% mucomyst is required to preare
5 cc of 5% mucomyst?
 ALTERNATIVE: solve for mg/ml
 EXAMPLE: Usual dose of albuterol sulfate is 0.5 ml of 0.5%
strength solution. How many mg is this?