help with a dosage calculation?

KrCmommy522, BSN, RN · Dec 17, 2017

When a solution is given in a percentage it is weight/volume, for example, 1% solution, means that in every 100 mL of solution you will find 1 g of drug.

Some Information:

A percentage of a solution tells you how many parts of the drug there are in 100 parts of solution. For example, a 1% solution means that there is 1 part of the drug in 100 parts of solution.

You use mL for liquids, and you use grams for tablets or powders. So, when the drug is liquid form, it is mL. When a drug is in powder or tablet form, it is in g.

Example for Liquids:

5% acetic acid = 5 mL of acetic acid in 100 mL of solution.

Example for Tablets or Powders:

12% potassium permanganate solution = 12 g potassium permanganate in 100 mL of solution.

A little bit more detail:

For fluid mixtures prepared with a dry medication, the percent strength represents the number of grams of the medication contained in 100 mL of the mixture.

Example: How much hydrocortisone powder is in a 2% hydrocortisone lotion? Each percent represents 1 g of hydrocortisone per 100 mL of lotion. So, a 2% hydrocortisone lotion will contain 2 g of hydrocortisone powder in every 100 mL. So, a 2% hydrocortisone lotion will contain 2 g of hydrocortisone powder in every 100 mL of hydrocortisone lotion.

For fluid mixtures prepared with a liquid medication, the percent strength represents the number of mL of medication contained in 100 mL of the mixture.

Example: How much ethanol is in a 30% ethanol solution. The percent strength tells you that every 100 mL of the solution contains 30 mL of ethanol. So, a 30% ethanol solution will contain 30 mL of ethanol in every 100 mL of solution.

For solid or semisolid mixtures prepared with a dry medication, the percent strength represents the number of grams of the medication contained in 100 g of the mixture.

Example: How many grams of hydrocortisone powder are in a 1% hydrocortisone ointment? Each percent represents 1 g of hydrocortisone per 100 g of ointment. So, a 1% hydrocortisone ointment will contain 1 g of hydrocortisone powder in every 100 g.

For solid or semisolid mixtures prepared with a liquid medication, the percent strength represents the number of mL of medication contained in 100 g of the mixture.

Some more examples:

Lidocaine 2%. That means there are 2 g in 100 mL (or 2000 mg in 100 mL if you want to make it into mg).
0.9% sodium chloride means that there are 0.9 g per 100 mL.
0.45% sodium chloride means that there are 0.45 g per 100 mL
1.5% means that there are 1.5 g per 100 mL.

Now for your problem:

Order: Sulfate 500 mg

Supply: Ampule 50% 2 mL size

You need to determine the number of grams of sulfate in order to solve this problem. Using the 50%, how many grams of sulfate are there? You change this to mg in order to solve the problem.

Then you can figure out the dosage using the order of 500 mg and the supply of mg/mL.

Let me know if you have more questions.Just show me what you figure out from what I've told you! Good luck!