After assessing a client, a primary healthcare provider prescribes diphenhydramine 25 mg IV STAT for anaphylaxis. The pharmacy supplies a vial with a concentration of 50 mg/mL.
How much and when should a nurse administer this medication?

This answer is correct because it is based on a series of unit conversions and calculations. The nurse should follow these steps to provide safe medication to the child:

1) Convert the child's weight from pounds to kilograms by dividing by 2.2, since there are 2.2 lbs in 1 kg. The child weighs 20 kg.

2) Multiply the prescribed dose per kilogram by the child's weight in kilograms to get the total dose in milligrams. The child needs 40 mg of pyrimethamine.

3) Use the ratio given on the drug label to convert the total dose in milligrams to the volume in milliliters. The nurse can set up a proportion as follows:

1 mg / 5 mL = 40 mg / x mL

Cross-multiplying and solving for x gives:

x = 200 mL

Therefore, the nurse should administer 200 mL of medication to deliver 40 mg of pyrimethamine to the child.

4) Convert the volume in milliliters to the volume in teaspoons by dividing by 5, since there are 5 mL in 1 tsp. The nurse should administer 40 tsp of medication to the child.

5) Convert the volume in teaspoons to the volume in cups by dividing by 48, since there are 48 tsp in 1 cup. The nurse should administer 0.83 cups of medication to the child.

This numeric form is appropriate, according to the Joint Commission, because it does not use a trailing zero after a decimal point, which is a common cause of medication errors and should be avoided. A trailing zero may be misread or misinterpreted as a larger dose or omited altogether, resulting in a 10-fold overdose or underdose, respectively. For example, when prescriptions have been writen for "Coumadin 1.0 mg," patients have received 10 mg in error¹². Therefore, the Joint Commission requires that a trailing zero may be used only when required to demonstrate the level of precision of the value being reported, such as for laboratory results, imaging studies that report the size of lesions, or catheter/tube sizes. It may not be used in medication orders or other medication-related documentation.

The other options are not appropriate numeric forms because:

a) 3.0 uses a trailing zero after a decimal point, which poses a risk of confusion or error.

b) 0.30 uses a trailing zero after a decimal point, which poses a risk of confusion or error.

c) 0.03 is not equivalent to 0.3, as it is 10 times smaller.