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# Dosage Calculation Using Ratio And Propo

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### Dosage Calculation Using Ratio And Propo

1. 1. Calculate with Confidence 5 th edition Gray Morris Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
2. 2. Dosage Calculation Using the Ratio and Proportion Method Unit Three: Chapter 14 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
3. 3. Dosage Calculation Using Ratio and Proportion Method: Objectives <ul><li>After reviewing this chapter, you should be </li></ul><ul><li>able to: </li></ul><ul><ul><li>State a ratio and proportion to solve a given dosage calculation problem </li></ul></ul><ul><ul><li>Solve simple calculation problems using the ratio and proportion method </li></ul></ul>
4. 4. Use of Ratio and Proportion in Dosage Calculation <ul><li>Often need to find a single “unknown” in med calculations </li></ul><ul><ul><li>Example: Available dose is 50 mg in 1 mL, ordered dose is 25 mg—one “unknown”: x mL </li></ul></ul><ul><li>State known first, then unknown </li></ul><ul><li>Sequence must match </li></ul><ul><ul><li>Example: mg : mL = mg : mL (left sequence matches right sequence) </li></ul></ul>
5. 7. Ratio and Proportion: Key Points <ul><li>Convert everything into same unit of measure before starting calculations </li></ul><ul><li>Convert to the unit of measure in which the medication is available </li></ul><ul><li>Convert in the direction that eliminates decimals whenever possible—decimals are sources for error </li></ul>
6. 8. Ratio and Proportion: Key Points (cont’d) <ul><li>State “known” or “available” first </li></ul><ul><li>State “unknown” or “desired” second </li></ul><ul><li>Keep left and right sides in matching sequence </li></ul><ul><ul><li>mg : mL = mg : mL </li></ul></ul><ul><li>Label all terms, including x </li></ul><ul><li>Make mental “estimate” of logical answer first </li></ul>
7. 9. Convert to Same System First <ul><li>Order: Phenobarbital gr i p.o. at bedtime </li></ul><ul><li>WRONG! </li></ul><ul><li>60 mg : 1 tab = gr i : x tab </li></ul><ul><li>RIGHT </li></ul><ul><li>Conversion: gr i = 60 mg </li></ul><ul><li>60 mg : 1 tab = 60 mg : x tab </li></ul><ul><li>x = 1 tab </li></ul>
8. 10. Convert Toward No Decimals <ul><li>Order: Augmentin 0.25 g p.o. q8hr </li></ul><ul><li>WRONG! </li></ul><ul><li>500 mg : 1 tab = 0.25 g : x tab </li></ul><ul><li>RIGHT </li></ul><ul><li>Conversion Factor: 1 g = 1,000 mg </li></ul><ul><li>Therefore – 0.25 g = 250 mg </li></ul><ul><li>500 mg : 1 tab = 250 mg : x tab </li></ul><ul><li>X = ½ tab </li></ul>
9. 11. Ratio and Proportion: Key Points <ul><li>Label final answer for x in appropriate unit for delivering med (e.g. mL, tabs, caps) </li></ul><ul><li>Double-check work </li></ul><ul><li>Be consistent in set-up and performance of calculations </li></ul>