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1/17/2015 Pharmacy Feud: Calculations review for Pharmacy Technicians by Lara Nichols, PharmD, MPH Alaska Native Medical Center, Transitions of Care Pharmacist Objectives • 1. Review the conversion between American standard measurement to metric measurements for weight, volume and temperature • 2. Review dosage calculations for both retail and hospital medications • 3. Review IV flow rates calculations (ml/hr and gtt/min Learning assessment: Pretest 1. How many ounces are in 120ml of amoxicillin? 2. What is the acceptable temperature in Celsius that your refrigerator should register in the pharmacy? 3. If a patient weighs 100kg and his dose is 6mg/kg/day. How much total drug will he get per day? Conversions - Weight 1 kilogram = 1000 grams 1 kg = 1000 g Kilogram: largest measure of weight used in pharmacy. Used for patient weights. CATEGORIES • • • • • Conversions --- weight and volume Temperature --- Fahrenheit and Celsius Concentration --- mg/ml, percent and ratio Dosage Calculations --- retail and hospital IV Calculations --- flow rates (ml/hr and gtt/min) Conversions - Weight 1 gram = 1000 milligrams 1 g = 1000 mg Gram: Used to measure bulk quantities of drugs, e.g. bulk powders in the compounding area. A few drugs are dosed in grams. 1 1/17/2015 Conversions - Weight 1 milligram = 1000 micrograms 1 mg = 1000 mcg Conversions - Weight Factors of 1000 1 kg = 1000 g = 1,000,000 mg = 1,000,000,000 mcg (thousand) (million) (billion) Milligram: Used to measure most drug doses. Microgram: Used for doses of very potent drugs, e.g. levothyroxine, digoxin. Conversions - Weight Conversions - Weight Practice questions: 1. How many mg in a 1 g sucralfate tablet? 1 grain 1 gr = 65 milligrams (apx) = 65 mg (apx) 2. A premature baby weighs 2.5 kg. How many grams does the baby weigh? Grains are still used to measure doses for a few of the oldest drugs, e.g. aspirin and phenobarbital. 3. How many mcg of haloperidol in a 2 mg tablet? Conversions - Weight Conversions - Weight 1 ounce = 30 grams (apx) 1 oz = 30 g (apx) 1 kilogram = 2.2 pounds 1 kg = 2.2 lb Ounces are used to measure ointments and creams, e.g. a 1 oz tube of nystatin ointment. Patient weights are measured in kilograms. Your weight in kilograms is roughly half that of your weight in pounds. Example: 132 lb = 60 kg 2 1/17/2015 Conversions – Weight Practice Questions: 1. A 32.4 mg tablet of phenobarbital contains apx. how many grains of phenobarbital? 2. A 30 g tube of bacitracin ointment contains how many ounces of ointment? 3.If a baby weighs 6.6 lb, how many kg does it weigh? Conversions - Volume 1 Ounce = 30 milliliters (apx) 1 oz = 30 ml Ounces are used to measure bulk quantities of liquids. Conversions – Volume 1 liter = 1000 milliliters 1 L = 1000 ml A liter is approximately the same as a quart. A milliliter is about 1/5 of a teaspoon. 5ml = 1 tsp Milliliters are used in pharmacy to measure liquids of all types. Conversions - Volume Practice Questions: 1. An IV bag that contains half a liter of IV fluid contains how many ml? 2. An 8 oz bottle of shampoo contains how many ml of shampoo? Conversions - Review 1 kg = 1000 g 1 g = 1000 mg 1 mg = 1000 mcg 1 gr = 65 mg (apx) 1 kg = 2.2 lb 1 oz = 30 g or 30 ml (apx) 1 L = 1000 ml Temperature Freezing: 32 degrees Fahrenheit = 0 degrees Celsius 32 °F = 0 °C Boiling: 212 °F = 100 °C Body Temperature: 98.6 °F = 37 °C 3 1/17/2015 Temperature Conversions between Celsius and Fahrenheit: C = ( F – 32) x 5/9 Example: It’s 23 °F outside. What is that in °C? C = ( F – 32) x 5/9 C = (23 – 32) x 5/9 C = -9 x 5/9 = -9 x 5 = -5 °C 9 Temperature Celsius Fahrenheit Freezer Refrigerator -20 to -10° 2 to 8° -4 to 14° 36 to 46° Controlled Room Temperature 20 to 25° 68 to 77° Temperature It’s 30 °C outside. What is that in Fahrenheit? C = ( F – 32) x 5/9 30 = (F - 32) x 5/9 9 x 30 = (F – 32) x 5 x 9 5 9 5 270 = (F – 32) 5 54 = F - 32 F = 54 + 32 = 86 °F Concentration – mg/ml • Concentration = amount of drug per unit volume • Mg/ml is the most common way that concentration is expressed • 20mg/ml solution --- each milliliter contains 20mg of drug These are acceptable temperature ranges as defined by the USP. Concentration - Ratio • • • • • • • Concentration can also be expressed as a ratio The ratio is defined as grams per ml 1:1000 = 1 g / 1000 ml 1:100 = 1 g / 100 ml 1:10 = 1 g / 10 ml 1:200,000 = 1 g / 200,000 ml Epinephrine is one of the few drugs still expressed in ratio concentrations. Concentration – Ratio • Converting ratio concentrations to mg/ml • 1:1000 = 1 g / 1000 ml = 1000 mg/1000 ml = 1 mg/ml • 1:100 = 10 mg/ml • 1:10 = 100 mg/ml • Shortcut: Multiply numerator (top number) by 1000 and divide to get mg/ml 4 1/17/2015 Concentration - Percent • Concentrations can also be expressed as percents, or parts per 100. • Percent concentration is defined as g / 100ml. • 1 % = 1g/100ml = 1000mg/100ml = 10mg/ml • 10%=10g/100ml=10000mg/100ml=100mg/ml • Shortcut: To convert a % concn. to mg/ml, multiply by 10. • • • • Concentration Percent (g/100ml) Ratio (g/ml) Mg/ml 0.01% 1:10000 0.1 mg/ml 0.1% 1:1000 1 mg/ml 1% 1:100 10 mg/ml 10% 1:10 100 mg/ml 50% 1:2 500 mg/ml Concentration Dosage Calculations Most drugs are expressed as mg/ml Some drugs use other measures of “weight” Heparin and insulin are measured in units/ml Electrolytes are often measured in mEq/ml (e.g sodium bicarbonate) or mmoles/ml (e. g. potassium phosphate) • Set what you have or already know EQUAL TO what you want or need. • HAVE = WANT • Make sure units on both sides are the same. If not, convert. • Use cross multiplication to solve the equation. Dosage Calculations Dosage Calculations Example # 1 : Retail pharmacy Example # 2: Hospital pharmacy You have a bottle of diphenydramine oral solution that is labeled “12.5 mg / 5ml”. The Rx reads “Take 50 mg bid po for 5 d”. (take 50mg twice daily by mouth for 5 days) What is the patient’s dose in ml? How many ml total are needed to fill the Rx? HAVE = WANT 12.5 mg = 50 mg 5 ml x ml Units on both sides match. Cross multiply. 12.5 (x) = 5 (50) 12.5 (x) = 250 x = 20 ml is the patient’s dose. To fill the Rx: 20 ml x 2 doses/day x 5 days = 200 ml You have a vial of calcium gluconate labeled “10%”. Your IV label says to prepare an IV with 2 g calcium gluconate in 100ml NS. How much calcium gluconate do you need to draw up? HAVE = WANT 10 % = 2 g x Change 10 % to mg/ml. Change 2 g to mg. 100 mg = 2000 mg ml x 100 (x) = 2000 (1) x = 20 ml 5 1/17/2015 Dosage Calculations Example # 3: Dosing by weight A baby weighs 8.8 lb. The baby has an order for furosemide 20mg/kg/day, to be given every 6 hours. What is the baby’s daily dose? How much will it get every 6 hrs? HAVE = WANT 20 mg = x__ kg 8.8 lb Units are not the same. Convert lb to kg. ( 1 kg = 2.2 lb) 20 mg = x kg 4 kg 20 (4) = x (1) x = 80mg daily Every 6 hours = 4 times daily 80mg/4 = 20 mg every 6 hours IV Calculations • Finding the flow rate • Use FLOW RATE = VOLUME / TIME • Example: an IV is 500ml and is given over 2 hours. What is the flow rate in ml / min? • flow rate = volume / time • Flow rate = 500 ml / 2 hours • Convert hours to min (1 hour = 60 min) • Flow rate = 500 ml / 120 min • Flow rate = 4.2 ml / min IV Calculations Example # 2: An IV is running at 10ml/min. Total volume is 1000 ml. How long will it run in hours? FLOW RATE = VOL/TIME 10 ml = 1000 ml 1 min x min Units are the same. 10 (x) = 1000 (1) x = 100 min. Convert min to hours (1 hour = 60 min) HAVE = WANT 1 hour = x__ 60 min 100 min 1 (100) = x (60) 100 / 60 = x = 1.67 hours IV Calculations • FLOW RATE = VOLUME / TIME • Examples of IV flow rates: 60 ml / hr 1 ml / min The flow rate tells how rapidly the IV is being administered. IV Calculations Finding the duration of an IV (how long will it run?) Use FLOW RATE = VOLUME / TIME Example #1: A Protonix drip is running at 25 ml/hr. It is a 250ml IV bag. How long will it run? FLOW RATE = VOLUME / TIME 25 ml = 250 ml 1 hr x hr Units are the same. 25 (x) = 250 (1) x = 10 hours IV Calculations IV sets are calibrated in gtt/ml (drops/ml). Typical sets are 10, 15, 20 or 60 gtt/ml. Pharmacy uses a flow rate of ml/hr or ml/min But nurses use flow rates of gtt/min. Steps: 1. using FLOW RATE = VOLUME / TIME, find the flow rate for the IV in ml / min 2. Multiply flow rate (ml / min) by the set calibration ( gtt / ml). Answer will be flow rate for IV in gtt / min. ml x gtt = gtt min ml min 6 1/17/2015 IV Calculations IV Calculations Example: A nurse has an IV of 150ml that needs to be infused in 1 hour using a set that is calibrated at 15 gtt/ml. What should she set the drip rate at (in gtt/min)? FLOW RATE = VOL / TIME 150ml / 1 hour = 150 ml / 60 min = 2.5 ml / min 2.5 ml x 15 gtt = 37.5 gtt / min min ml Another example: Nurse has an IV of 150ml of NS to administer over 3 hours. She is using a set calibrated at 60 gtt/ml. What flow rate in gtt/min should the nurse use? Flow rate = volume / time 150 ml / 180 min = 0.83 ml / min 0.833 ml min x 60 gtt = 50 gtt/min ml Questions? Category: Weight and Volume Conversion Conversion • 1. How many mcg in a mg? • 2. How many mg in 2 g? • 3. How many ml in an ounce? • 4. How many ounces in 120 ml? • 5. How many lb in a kg? • 6. How many ml in a liter? 7 1/17/2015 Conversion Category: Temperature • 1. Which is larger: a mg or a mcg? • 2. If patient weighs 50 kg: is it a baby or an adult? • 3. How many mg are in half a gram? • 4. If an adult weighs 50kg, are they fat or thin? • 5. How many grams in a 2 oz tube of cream? • 6. A 64.8 mg tablet is how many grains? Temperature • 1. Water freezes at ? °C • 2. Water boils at ? °C ? °F ? °F Temperature 1. - 4 °F is how many degrees C? 2. A properly working refrigerator should register between what range in °C? 3. A properly working refrigerator should register between what range in °F? • 3. Body temperature is ? °C ? °F 4. If the A/C is broken and the pharmacy is at 90 °F, is it too hot to store drugs safely? • 4. Give the formula to convert between °C and °F. 5. If the heat is broken and the pharmacy is at 55 °F, is it too cold to store room temperature drugs? • 5. 50 °C is how many °F? 6. The freezer is registering -5 °C. Is it working properly? • 6. Which is lower, 0 °C or 0 °F? Category: Concentration Concentration 1. D5 is what percentage strength of dextrose? How many mg/ml is this? 2. 20% is how many mg/ml? 3. A 5 % tube of ointment has how many mg of drug in each mg of ointment? 4. 1:100 is the same as how many mg/ml? What percent? 5. What is 10% written as a ratio concentration? 6. What is 0.1% written as a ratio concentration? 8 1/17/2015 Concentration Category: Dosage Calculations 1. A vial label says “40 mEq in 20ml”. How many mEq in 1 ml? 2. 900mg/6ml is equivalent to how many mg/ml? What percent concentration? 3. A solution that is 5% strength has how many mg/ml? 4.Which is more concentrated: 1:100 or 1:1000? 5. Which is more concentrated: 1:1000 or 1mg/ml? 6. Normal saline is what percentage strength of sodium chloride? How many mg/ml is this? Dosage Calculations 1. You have a 2 mg/ml solution of Drug X. Patient needs 4 mg. How many ml is this? Dosage Calculations 1. A prescription states “Take 1 cap q 6hr”. How many caps for a 10 day supply? 2. A prescription states “Take 3 ml po ac for 10 days”. How many ml to dispense? 2. Now the patient needs a 5 mg dose. How many ml? 3. Now the patient needs a 1 mg dose. How many ml? 3. A patient weighs 100 kg. Their dose is 3mg/kg/day. How many mg will they get in a day? 4. If this drug is to be given 3 times a day, how many mg will be in each dose? 4. An IV needs 100 mg of Drug X added to it. How many ml to add? 5. A prescription states “Take 2 tabs bid”. How many tablets for a 30 day supply? 5. A baby weighs 4.4 lb. It needs Drug Z dosed at 15mg/kg/day. How much drug will baby receive daily? 6. If Drug Z is to be given q 4 hr, how many mg in one dose? 6. A prescription states “Take 3 tabs qhs”. How many tablets for a 90 day supply? Category: IV Calculations IV Calculations 1. Give the basic formula used in all IV calculations. 2. What is the flow rate in ml/hr for an IV of 600 ml to be given over 10 hours? 3. What is the flow rate in ml/min for this IV? 4. How long will it take for a 1000ml IV running at 200ml/hr to run out? 5. How long will it take for a 100 ml IV running at 2 ml/min to run out? 6. The doctor told the nurse to infuse 500ml of D5 at 50ml/hr. The bag has been hanging for 2 hours and has run out. Is there a problem? 9 1/17/2015 IV Calculations 1. Pharmacy IV labels typically have flow rates in ? 2. If a nurse is manually setting the flow rate, she will typically use a flow rate in ? 3. If an IV is to run at 1 ml/min and the nurse has a set calibrated at 10gtt/ml, she should set the flow rate at ? 4. A flow rate of 90 ml/hr is how many ml/min? 5. If an IV is to run at 90 ml/hr with a set calibrated at 30 gtt/ml, what will be the flow rate in gtt/min? Learning assessment: Posttest 1. How many ounces are in 120ml of amoxicillin? 2. What is the acceptable temperature in Celsius that your refrigerator should register in the pharmacy? 3. If a patient weighs 100kg and his dose is 6mg/kg/day. How much total drug will he get per day? 10