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Conversions: Between and Within Systems

Conversions: Between and Within Systems. Textbook Assignment: Pickar, G. (2007). Dosage calculations: A ratio-proportion approach. (2nd ed.) Chapter 4. Revised KBurger0808. Equivalents. 1 grain (gr) = 60 milligrams (mg) 1 teaspoon (t) = 5 milliliters (mL)

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Conversions: Between and Within Systems

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  1. Conversions: Between and Within Systems Textbook Assignment: Pickar, G. (2007). Dosage calculations: A ratio-proportion approach. (2nd ed.) Chapter 4 Revised KBurger0808

  2. Equivalents 1 grain (gr) = 60 milligrams (mg) 1 teaspoon (t) = 5 milliliters (mL) 1 tablespoon (T) = 3 teaspoons (t) 1 ounce (oz) = 30 milliliters (mL) 1 cup = 8 ounces (oz) 1 Kilogram (Kg) = 2.2 pounds (lbs) 1 liter (L) = 1000 milliliters (mL) 1 gram (g) = 1000 milligrams (mg) 1 milligram (mg) = 1000 micrograms (mcg) The equivalents listed in blue are only considered approximate equivalents

  3. Converting Using Ratio-Proportion • Rule • Recall equivalents • Set up a proportion of two equivalent ratios • Cross-multiply to solve for an unknown quantity, X

  4. Converting Using Ratio-Proportion • Remember • Each ratio in a proportion must have the same relationship and follow the same sequence • A proportion compares like things to like things

  5. Converting Using Ratio-Proportion • Remember • The units of measurement in both numerators and denominators must match • ALWAYS, ALWAYS, ALWAYS label the measurement units in each ratio INCLUDING your unknown quantity X

  6. Converting Using Ratio-Proportion • Example • How many feet are in 36 inches?

  7. Recall equivalent Set up a proportion of two equivalent ratios Cross multiply to solve for “X” Label units to match the unknown “X” Converting Using Ratio-Proportion

  8. Recall equivalent Set up a proportion of two equivalent ratios Cross multiply to solve for “X” Label units to match unknown “X” Using Ratio Proportion to Convert Within Metric System EXAMPLE: Convert 5 grams to milligrams

  9. Converting Within the Metric SystemShort Cut • Medication conversions within the metric system most often occur between: mg and mcg [ mg are larger than mcg ] g and mg [ g are larger than mg ] L and mL [ L are larger than mL] • These are all 3 decimal place differences[ a difference of 1000 ] • To use this Short Cut you will need to remember-which unit is larger-to always move 3 decimal places

  10. Conversion Slide • Keep this visual in mind when converting within the metric system Move decimal point three places between each unit g kg mcg mg

  11. Converting Within Metric SystemShort Cutcontinued • Write out the desired equivalent in this format 5 mg = ______ mcg • Then draw an arrow that starts at the larger unit and points toward the smaller unit Larger to Smaller • Move the decimal point in the direction of the arrow by three places.

  12. Calculating a Drug Dosage that requires Conversion between Systems • Drug order reads Codeine sulfate gr ¾p.o. q.4h p.r.n., pain • Drug supplied is Codeine sulfate 30 mg per tablet • Calculate one dose

  13. Converting to Same System • Drug order reads Codeine sulfate gr ¾p.o. q.4h p.r.n., pain • Drug supplied is Codeine sulfate 30 mg per tablet • What do you notice? • Different system • Needs to be converted

  14. Approximate Equivalent: gr i = 60 mg • Step 1. Convert • Convert to equivalent units in the same system of measurement. Convert gr to mg. • Approximate equivalent: gr i = 60 mg.

  15. Convert usingRatio Proportion Method • Start by writing a known ratio: 1 grain = 60 mg [ the known equivalent ] • Then fill in the rest of the proportion • Solve for X1 gr¾ gr 60 mg = X mg1X = 60 x ¾ (0.75)X = 45 mg • Codeine gr ¾ = 45 mg

  16. Think • Step 2Stop and think carefully about what a reasonable dosage should be:You have just figured out that the doctor ordered 45 mg. The drug label indicates that each tablet = 30 mg.Will you be giving more or less than 1 tablet? MORE

  17. Step 3: Calculate usingRatio Proportion Method • Start by writing known ratio from the problem • Complete the proportion with other information you have [doctor’s order ] • Check for matching units. Cross multiply and solve for X • 30mg45mg 30X = 45 1 tablet = X tablet X = 45 = 1 15 = 1 ½ tablets 30 30

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