6/8/2016 Med-Math NUR 152 Mesa Community College

6/8/2016 How To Solve Dosage Problems It’s OK to solve the problem your way. Do not learn a new math method if your way works and you get the correct answer.

6/8/2016 Metric System Gram - the basic unit for weight –Kilogram (kg) –Milligram (mg) –Microgram (mcg) Liter – the basic unit for volume –Liter (L) –Milliliter (mL) Meter – the basic unit for length –Centimeter (cm) –Millimeter (mm)

Dosage Measurement Systems Measures of Weight –Gram: g –Milligram: mg –Microgram: mcg – g > mg 1 g = 1000 mg To multiply by 1000, move the decimal points three points to the RIGHT – mg < g 1000 mg = 1 g To divide by 1000, move the decimal point three places to the LEFT – mg > mcg 1 mg = 1000 mcg To multiply by 1000, move the decimal points three points to the RIGHT

6/8/2016 The Bad News! You will have to memorize the standard equivalencies measurement. –1 g = 1000 mg –1 mg = 1000 mcg –1 grain = 60 (65 in some texts) mg –1 kg = 2.2 lbs –1 tbs = 15 mL –1 tsp = 5 mL –1 oz = 30 mL

6/8/2016 Metric Liquid Measures Liter = L Milliliter – mL 1 teaspoon = 5 mL 1 tablespoon = 15 mL 1 ounce = 30 mL 1 pint = *approximately 500 mL 1 quart = *approximately 1 L = 1000 mL

6/8/2016 Decimals If a decimal fraction is not preceded by a whole number, always place a zero in front of it. Example: –.25 is always 0.25 –Avoids interpretation errors

6/8/2016 Decimals Never follow a whole number by a decimal point and a zero. Again, could result in a medication misinterpretation. Example: 25.0 Would be easy to read as 250.

6/8/2016 Apothecaries’ System Not as exact as metric system. Need to convert apothecary measures to metric by using an equivalency table. Unit of measurement is written before the number Example: six grains is gr 6 or gr vi

Apothecary System 1 hr 60 min ¼ hr 15 min ½ hr 30 min ¾ hr 45 min Use the clock to help you remember gr and mg. 60 mg = gr 1 60 min = 1 hr 15 mg = gr ¼ 15 min = ¼ hr 30 mg = gr ½ 30 min = ½ hr 45 mg = gr ¾ 45 min = ¾ hr

6/8/2016 Apothecary Units of Measurement Grains - gr Drams - ʒ (3.887 grams) Ounce Symbol- ℥ (31.03 grams)

6/8/2016 Conversions R/T Weight Body weight is needed to calculate accurate doses. Calculated in kilograms. 2.2 lbs = 1 kg To convert pounds to kilograms, divide by 2.2 and round to nearest tenth for adults, hundredths for pediatrics. To convert kilograms to pounds, multiple by 2.2 and round to nearest tenth for adults, hundredths for pediatrics.

Converting Ounces to decimals 8 lbs. 9 oz. does not equal 8.9 pounds! Must convert the oz. to decimals to make a proper equation 16 ounces in a pound 9 oz. = oz. 8 lbs + 9 oz. = lbs 6/8/2016

Rounding Rules Rounding is the last step of the problem. For medication dosing, round to the nearest tenth for adults and pediatrics Carry your division to at least two places (hundredths place) and round off at the end of the problem to the nearest tenth for Adult and Pediatric dosages. Pediatric weight in kilograms is rounded to the nearest one hundredth.

6/8/2016 Formula Method CALCULATING MEDICATIONS Desire X Vehicle = Amount Have Desire = Physician’s order Have = Strength of drug in container Vehicle= Form in which drug comes Amount = How much to give to the client

6/8/2016 Abbreviate the Formula D x V = A H

6/8/2016 Example Order: 0.25 g Supply: 0.5 g per tablet (D) 0.25 g x (V)1 tablet = ½ tab (H) 0.5 g

6/8/2016 Example Order: Lasix 60 mg po every day Stock: Scored tablets labeled 40 mg (D) 60 mg x (V) 1 tablet = 1 ½ tablets (H) 40 mg Can you give this? YES. Give one full tablet and break the other scored tablet in half.

6/8/2016 Conversions “Desired” and “Have” must be in the same weight measure in order to do the problem. Cannot be g and mg. You must CONVERT the “desired” weight measure to the weight measure on the drug label you “have”.

Conversion Problem Order: 0.25 g Supply: 125 mg per tablet 1 st step: Convert grams into mg g > mg 0.25 g = 250 mg (D) 250 mg x (V) 1 tablet = 2 tablets (H) 125 mg YOU MUST LABEL THE ANSWER IN THE FORM THE MED COMES IN! CIRCLE YOUR ANSWERS ON YOUR TEST

6/8/2016 Practice Problem The order reads: Zithromax oral suspension 400 mg po qd x 4 days How would you set up this problem?

6/8/2016 D x V = A H 400 mg X 5 mL = A 200 mg 2 X 5 = 10 mL

6/8/2016 Let’s Practice Group work on Medication Problems