Summary

The dose specified in a medication order may not be the same dose for the medication that you have on hand. Therefore, you must calculate a new dose that is proportional to the prescribed dose.

All doses are calculated using the metric system. You must be able to convert within the metric system and convert between household measurements and metric because patients are likely to self medicate using household measurement—such as a teaspoon—rather than using metric measurements.

Converting between metric units is performed by moving the decimal to the left or right depending on whether you are moving from a smaller metric unit to a larger metric unit or vice versa. Converting between household measurements and metric is achieved by multiplying or dividing using a conversion factor. This depends on whether you are converting from household measurements to metric or vice versa.

There are two methods that are used to calculate a dose. These are the formula method and the ratio-proportion method. Both use the on hand dose of a medication to determine the desired dose based on the medication prescription.

The formula method and the ratio-proportion method are also used to calculate parenteral medications. Alternatively, parenteral medication can be administered through a vein either as a bolus or an infusion. If infusing through an intravenous line, the nurse must calculate the number of drops per minute the IV should run to deliver the amount of medication ordered.

We'll leave the topic of preparing medications and explore medications that are available in nature in the form of herbs. You'll learn about herbal therapy in the next chapter.

Quiz

1. Prescribed: Duricef 0.4G PO QID. On hand: Duricef 200 mg capsules. How many capsules do you need?

(b) 2 capsules

(c) 5 capsules

(d) 20 capsules

2. Prescribed: Ceclor 150 mg. On hand: Ceclor 300 mg tablets. How many tablets do you need?

(a) 30 tablets

(c) 50 tablets

3. Prescribed: 1000 mL of 0.9% normal saline (NS) intravenously every 8 hours. The intravenous tubing delivers 15 gtts/mL. How many gtts/min (drops per minute) will be infused?

4. Prescribed: Diabenese 600 mg. On hand: Diabenese 300 mg tablets. You need 2 tablets.

5. Ordered: 1 liter of NS q 7h. Available 1 liter of NS and IV tubing with a drip factor of 10. You would regulate the IV at 23.8 gtts/min.

6. Prescribed: Heparin 1000 units/hour intravenously. Available: Heparin 25,000 units/hour in 250 cc D5W. How many mL/hr should be administered to give the correct dose?

(d) None of the above

7. Prescribed: 1 liter of D5W q8h. Available: 1 liter of D5W and IV tubing 10 gtts/mL. You regulate the IV at 20.8 gtts/min.

8. Prescribed: 1000 mL of IV fluid q12h. Available: 1000 mL of IV fluid and microdrip tubing. How many gtts per minute will you regulate the IV?

9. Prescribed is Prilosec 4.4 mg/kg for a child who weights 88 lbs. Available is Prilosec 50 mg/5 mL. You would give the child 1.76 mL.

10. Prescribed is Ceclor 2 mg/kg for a child who weighs 20 lbs. Available is Ceclor 20 mg/2 mL. You would administer 1.8 mL.

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