Calculation skills

Question 1

What does 1% mean?

Answer 1

1% solutions have 1g of drug in 100mL

seen as either:

• 1g in 100mL
• or 10mg for 1mL (i.e. 1mL would contain 10 milligrams)

Question 2

How to calculate the volume needed to give a dose of drug?

e.g. 40mg of a drug produced in 80mg/2mL solution

Answer 2

Question 3

Hydralazine is presented as a 20 mg/2 mL ampoule.

how much NaCl is needed to be added to make a 1mg/1mL solution?

Answer 3

18ML

1mg/ml would be 20mg in 20mL so need to make up to that volume

Question 4

Are medications containing phenytoin base vs those with phenytoin sodium the same?

Answer 4

No

bioavailability is different with 100mg phenytoin sodium = 92mg phenytoin base

Question 5

What medications are affected by the so called “salt factor”?

Answer 5

• phenytoin
• digoxin
• sodium fusidate

Question 6

what is meant by the “salt factor” in relation to drug formulations?

Answer 6

Where formulations with a salt compound of the drug e.g. phenytoin sodium vs formulations with base version of drug have different doses to reach therapeutic effect

need to take care when converting from one to another

Question 7

orders to units

Answer 7

nanograms → micrograms → milligrams → gram → kilo

all by 1000