DRUG DOSE CALCULATION Dr.Soe Aung Myint .

Introduction Errors in calculating drug dosages can cause significant harm to patients, particularly neonates, infants and children, therefore it is essential.

Learning Objectives Ratios and Proportions Desired Dose…DD Concentration…….W/ V, W/ W ,V/ V Calculation The mL……(D / H )x Q(V)=amount to give Drip Rates……(mL x gtt factors) / minute Dopamine Drip Rates….(μg x Kg) / 25 Lidocaine Clock….60 gtt /set, 4mg/ mL Dosage Calculation….(D / H) x V(Q) =Amount to give

What are the human errors that can happen during a drug therapy? Why to know Drug Dose calculation?(high risk) What to know before calculating a dose?(Abbreviations and metric conversions) How to calculate the dose?(Formula) Examples of drug dose calculation

Type of medication Error Wrong…..Drug,Dose or freguency,route Wrong…...Formulation,Label,storage, omitted,passed expiry date Wrong……Patient - Allergic to Treatment Wrong…….Contraindication

Overview Abbreviation Metric Conversions Disired Dose Concentrations Drip Rates Medication (Dopamine and Lidocaine)

Abbreviations cc.cubic centimeter DD.Desired Dose gm.gram gtt.drop/drops IM.Intramuscular IO.Intraosseous IV.Intravenous IVP.Intravenous Push

Abbreviations Kg.Kilogram L.Liter mcg.microgram mEq.miliequivalent mg.miligram ml.mililiter µg.microgram µgtt.micro drop

Abbreviations D5NS – 5% dextrose in 0.9% sodium chloride Cl – Chloride Na – Sodium Mg – Magnesium K – Potassium SO4 – Sulfate mEq – milliequivalent mmol - millimole

Metric Conversions .Kg, g, mg, mcg (μg) Lbs to Kg L to ml

Kg, g, mg, mcg To convert if going from large value to smaller value, move the decimal point 3 places to right for each conversion. If going from smaller value to larger value move the decimal point 3 places to the left for each conversion. 3.0Kg=3→0 → 0 → 0 g=3000 g 3.0Kg→=3 → 0 → 0 → 0 → 0 → 0 → 0 mg=3,000,000 mg 3.0Kg=3-0-0-0-0-0-0-0-0-0 mcg=3,000,000,000 mcg (μg)

Lbs to Kg There are two methods that may be used to convert pounds to kg Lbs/2.2=Kg 3 a.m rule (Lbs/2) - 10%=Kg Therefore if you need to convert Kg to Lbs Kg x2.2= Lbs or (Kg x 2)+10%=Lbs

L to ml 1L=1→0 →0→0=1,000 mL 500mL=5←0←0=0.5L

Conversions to mg 300 mcg=0.3 mg (Small to Large value) 6 Kg =6,000,000 mg (large to small value) 450 g=450,000 mg 0.42Kg=420,000 mg 14 g= 14,000 mg 1,000mcg=1 mg Miligram (mg) is commonly used in medication.

Conversion to μg 1g =1,000,000 μg( Large to small value) 0.452 mg =452 μg 0.074 Kg =74,000,000 μg 0.010 mg =10 μg

mL v. cc A mL and cc have the same value. Therefore 1mL = 1cc 400cc=400mL

Basic Clinical Pharmacology It is important that you should pay full attention to this class. Solution is made up of solute(example ..NaCl) dissolved in a solvent (example..water).

Expression of Strengths Percent(%) Solution contains = grams per 100ml of solution Example….1%atropine = 1g/dl …..2%lignocaine=2g/dl Ratio Solution(Example..1:1000)means=1gm of solute in 1000ml of solvent 25%Glucose Solution=25g/100ml=(25x1000mg)/100ml=250mg/ml 1:1000 adrenaline =1g/1000ml=1000mg/1000ml=1mg/1ml

Ratios and Proportions A ratio states a relationship between two quantities. Example: 5 g of dextrose in 100 ml of water (Dextrose 5% in Water often abbreviated as D5W) A proportion is two equal ratios Example: 5 g of dextrose in 100 ml of water equals 50 g of dextrose in 1000 ml of water 5 g 50 g 100ml = 1000ml If you know three of the four terms you can calculate the fourth.

Ratios and Proportions A vial of drug contains 40mg/2ml. How many milliliters (ml) are required to obtain 300mg of drug? 1. 40mg = 300mg 2. (40mg)(X)= (2ml) (300ml) 2ml X 3. X = (2ml)(300mg) 4. X=15ml (40mg)

Concentrations and Dilutions Terminology - 5% dextrose in water is the same as D5W. - 0.9% sodium chloride (NaCl) is the same as normal saline (NS). - Half-normal saline is half the strength of normal saline (0.9% NaCl), or 0.45% NaCl. - This may also be referred to as 1/2NS

Concentrations and Dilutions Concentration expressed as percentage Percent weight-by-weight (w/w) is the grams of drug in 100 grams of the product. Percent weight-by-volume (w/v) is the grams of drug in 100ml of the product. Percent volume-by-volume (v/v) is the milliliters of drug in 100ml of the product.

Examples Example 1: 0.9% sodium chloride (w/v) = 0.9 g of sodium chloride in 100 ml of solution. Example 2: 5% dextrose in water (w/v) = 5 g of dextrose in 100 ml of solution. Example 3: 23.4% sodium chloride (w/v) = 23.4 g of sodium chloride in 100 ml of solution

Examples Example 4: How many grams of dextrose are in 1 L of D5W? Known ratio: D5W means 5g in 100ml Unknown ratio: X in 1000ml Write the proportion and solve for X: X 5g X = 50 g 1000ml = 100ml

Desired Dose The amount of a particular medication to be administered. The symbol “/” stands for per

Desired Dose A patient with chest pain needs to be given 4 mg of Morphine Sulfate for Chest Pains. 4 mg is the Desired Dose

Desired Dose A hypotensive patient needs to be given Dopamine at 10μg/kg/minute IV, patient weight is 220 Lbs (220/2.2)=100Kg 1,000 μg/min is the desired dose.

Concentration The concentration is found by dividing the weight by volume (Ex..50 mg/2mL) The answer will result in the concentration /ml of medication (50/2)=25 25 mg/ml

Concentration Phenergan is ordered 12.5 mg.It is supplied 25 mg/2mL.What is the concentration? (w/v) 12.5 mg/ml

Concentration Lidocaine is ordered at 2 mg/min. It is supplied 2g/500 mL. What is the concentration? (w/v) 0.004 g/ml or 4 mg/ml

Calculation the mL to be given There is a very simple mathematical equation to calculate the mL to be given. (D/H) x Q (or) V Dose you want to give (mg/μg) What do you Have it supplied in (mg/μg) What Quantity does it come in (mL)

Medication Calculation Phenergan is ordered 12.5 mg. It is supplied 25 mg/2 mL. How many mL will you need to give? (D/H) x Q(V) Dose you want to give is 12.5mg(D),supply is 25mg(H) and quantity(volume) is 2ml(V) (12.5 mg/25 mg) x2 mL 0.5 mg x 2 mL 1mL

Adenosine is ordered 12 mg IVP after no response to 6 mg dose Adenosine is ordered 12 mg IVP after no response to 6 mg dose. Adenosine is supplied 12 mg/4 ml. How many ml will you need to give? (D/H) x Q (V) (12/12) x 4 4 mL

Lidocaine is ordered 1 mg/kg to a patient that weights 150 Lbs Lidocaine is ordered 1 mg/kg to a patient that weights 150 Lbs. It is supplied 100 mg/5mL.How many mL will you need to give? (D/ H) x Q (V) Dose you want to give is 1mg/kg …for 150lbs(or)68.18kg patient =68.18mg(D),supply is 100mg(H) ,Quantity is 5ml(V) 150/2.2=68.18Kg, (68.18mg/100mg)x5mL 3.4 mL

Drip Rates First, remember that you are going to be mixing a medication into fluids, you must first withdraw the amount of fluid from IV bag that you will be replacing with the medication, so that the concentration will remain the same originally calculated.

For example, if lidocaine comes 1g/25 mL,you will mix 1g in your 500mL IV bag, first withdraw 25 mL of fluid from IV bag, then replace it with the 25mL containing to 1g of lidocaine. The volume will still be 500.Otherwise it would be 525 altering the mg/min you will give.

Drip Rates (mL x gtt factors)/minutes Example: 500 mL using 15 gtt set over 1 hour (500x15)/60= 125 gtts/min

Drip Rates A physician orders 500 mL LR to be infused over 2 hours.You have a 15 gtt IV tubing set.How many gtts/minute will you give? (mL x gtt factors)/ minutes 500 is (mL), 15 is (gtt factors) ,2hrs is 12o(min) (500 x 15)=(7500)/120=62.5 63 gtts/min(Ans)…….Another way ………1ml is 15gtts so 500ml is 7500gtts is needed for within 120min…so 63 gtts for 1min

Dopamine In order to give the correct dose, you must first find the concentration. Remember to use a 60 gtt IV tubing set when you are giving medications 60 gtt IV tubing set=1 mL=60 drops Although there are several ways to determine gtts/min, the easiest way to determine gtts/minute of dopamine, if using a (1600μg/ml concentration) is (μ g x Kg)/25 μgxKg/25

Dopamine A patient with impaired renal function is to receive 2μg/kg/ min. You have 800mg of Dopamine and a 500mL IV bag of Normal saline, along with 60 gtt IV tubing set. Your patient weights 250 Lbs. How many gtts/minute will you give? (μ g x Kg)/ 25……2(mcg) is needed for 1kg,250lbs is 113.63kg(Kg) (2μg x113.63)=227.26 ( 227.26)/25=9 9 gtts/min

Lidocaine The use of the lidocaine clock is easiest to use. The use of a 60 gtt/set is required to use the clock. You concentration must also be 4 mg/ mL.

Lidocaine Clock 4mg=60gtts 3mg=45gtts 2mg=30gtts

Lidocaine A patient with multiple PVC’s is to receive 2 mg/minute of Lidocaine. You have 1g and a 250mL bag of normal Saline, along with a 60 gtt set. How many gtts/minute will you give? Lidocaine 1g(1ooomg)/250ml is concentration 4mg/ml..,1ml is equal 60drops..,4mg is 60drops….2mg is 30gtts/min(Ans) 4mg---1mL—60 gtts(Lidocaine clock) 2mg---0.5mL---30 gtts 30 gtts/min(Ans)

Drug Dose Calculation Part (2)

Dosage Calculations Using Dimensional Analysis Anyone can do it!

Outcomes: Understand the learning components needed for student’s success in performing dosage calculations. Utilize dimensional analysis to calculate dosage. Potential resources for teaching dimensional analysis in the classroom.

Ways to calculate dosage: Formula Method Amount to Give Challenge: Must remember the extra step of changing D and H to same unit of measurement. Also may have extra variables such as body weight, times per day, etc.

Ways to calculate dosage: Ratio and Proportion Linear Ratio and Proportion Fractional Ratio and Proportion 500mg : 1 tab :: 1 g : x tabs Product of the means equals the product of the extremes. The products of cross multiplication in a proportion are always equal

Dimensional Analysis Dimensional Analysis involves setting up a series of fractions. All information is in one problem Students do not have to remember multiple steps Students ask four simple questions to set up their dimensional analysis problem.

Necessities for Student Success in Dosage Calculations Review of basic math functions – fractions and decimals Adding Subtracting Multiplication Division Students must memorize equivalents

The 4 main questions What is the order? (D) What is on hand? (H) Do you need any equivalents? Where are you going? (or what are you being asked to give?)(V)or(Q)

Start with conversion 240 mg = ______ grains

Start with conversions 240 mg = ______ grains 4 4 grains 1

Order: Lasix 40 mg PO daily Dose on Hand: 80 mg/10 ml What is the order?(D)

Order: Lasix 40 mg PO daily Dose on Hand: 80 mg/10 ml What is on hand?(H)

Order: Lasix 40 mg PO daily Dose on Hand: 80 mg/10 ml Do you need any equivalents?

Order: Lasix 40 mg PO daily Dose on Hand: 80 mg/10 ml Where are you going? (or what are you being asked to give?)(V)or(Q)

Order: Lasix 40 mg PO daily Dose on Hand: 80 mg/10 ml Begin by cross canceling labels

Order: Lasix 40 mg PO daily Dose on Hand: 80 mg/10 ml Labels left should be “what you are looking for”

Order: Lasix 40 mg PO daily Dose on Hand: 80 mg/10 ml Do the math 1 5 5 2 1

Choose your method You can use ratio,proportion and fractions method or formula method in drug dose calculation. The options you need to choose which you like best It doesn’t meeter the answer will be the same

What about problems with different units of measurement? Order: digoxin elixir 0.05 mg PO daily Label: Digoxin 50 mcg per ml How many milliliters will you give?..(D/H)x V 20 ml 1 1

Complex Problems Order: Augmentin 12.5mg/kg PO every 12 hours. Child weighs 22 lbs. Pharmacy sends a 75 ml bottle of Augmentin labeled 125mg/5ml. How many milliliters will you pour from the bottle?.....(D/H) x V….. 5 ml

Augmentin Dose you want to give is 1kg for 12.5 mg Therefore 22lb (or) 10kg for 125mg(D) 125mg is (H)…dose on hand 5ml is (V)… Put into the formula……..(D/H) x V………(125/125) x 5) is 5ml(Answer)

25 What about IV problems? Order: 250ml 5% D/W IV in 2.5 hours. Tubing package reads 15 gtts/ml. How many gtts/min will you adjust the IV? (mLxgtt factors)/minute 25

Physicians order Daypro 1200 mg bid. cap 1

Order: Estratab 1250mcg daily 1.25 mg=1250 mcg

The order reads: Administer 1000cc of D5NS over 10 hrs The order reads: Administer 1000cc of D5NS over 10 hrs. The drop factor on your tubing is 15 gtts/cc. How many gtts/min? …..(ml xgtt factors)/min 25 1 25 gtts/min 4 or 1

Questions For Practice

Desired Dose(Q1) A paediatric patient is to receive Atropine 0.02 mg/kg, patient weight is 18Kg .What is the DD? 0.02 x 18 =0.36 0.36 mg

Concentration(Q2) Dopamine is ordered 5μg/kg/min to a 220Lbs patient. It is supplied 800 mg/500 mL. What is the concentration? (w/v) 800/500=1.6 1.6 mg/ml or 1600μg/mL

(Q3) Amiodarone is ordered 150 mg IVP over 10 minutes.It is supplied 200 mg/10 mL How many mL will you need to give? (D/H) x Q(V)=150/200x10=7.5 7.5 mL

(Q4) Epinephrine 0.3 mg 1:1,000 SQ is ordered to a patient with anaphylaxis.It is supplied 1 mg/1 mL.How many mL will you need to give? (D/H) x Q(V)=0.3/1x1=0.3 0.3 mL

Drip Rates(Q5) A physician orders 200mL of 0.9% Sodium Chloride be infused over one hour. You have a 10 gtt IV drip set. How many drops/minute will you give? (mL x gtt factors) /minutes (200 x 10)=(2000)/60=33.33 33 gtts/min

Dopamine(Q6) A hypotensive patient is to receive 10μg/kg/ min. You have 400 mg of Dopamine and 250 mL Normal Saline, along with a 60 gtt set. Your patient weights 220 Lbs. How many gtts/minute will you give? (μ g x Kg)/25 10μg x(220/2.2)=1000 (1000)/25=40 40 gtts/minute

Lidocaine(Q7) After successful resuscitation of a patient in V Tachy,you are ordered to start a Lidocaine drip at 3mg/ min. Your premixed Lidocaine is packaged 2g/500mL.You also have a 60 gtt set. How many gtts/min will you give? 4mg---1mL----60 gtts(lidocaine clock) 3mg---3/4mL—45 gtts 45 gtts/minute

Your patient may receive Dilaudid 3 mg IM q3h for pain Your patient may receive Dilaudid 3 mg IM q3h for pain. Dilaudid is supplied in 1-ml ampules containing 4 mg. How many milliliters will you administer?..(D/H )x V ¾= 0.75 ml

The physician orders heparin 2500U SQ. You have heparin, 5000U per ml The physician orders heparin 2500U SQ. You have heparin, 5000U per ml. How many ml will you administer? ..(D/H) x V 1 ml 2

Your patient needs morphine gr 1/6 SQ stat for chest pain Your patient needs morphine gr 1/6 SQ stat for chest pain. You have a 20 ml vial labeled 15mg/ml. How many milliliters will you give?..(D/H) x V ml 0.67

A patient with tachycardia has an order for Brevibloc to be started at 50 mcg/kg/min. The concentration is Brevibloc 5 g in 500ml of D5W. The patient weighs 176 pounds. How many ml/h should the IV pump be programmed for?..(D/H) x V 24 ml/hr 1 2 25 12 1 80 24 1 2 40 1 1 1

Exercise (Q.1)..Aminophylline IV 10ml containing 25mg/ml was given to asthmatic Patient weighing 50 Kg in 10 minutes.Calculate the dose of aminophylline in mg/kg/min. Dose of amino is 25mg/ml So that in 10ml,dose= 250mg In 50 kg----------250mg In 1 kg------------250/50=5 mg In 10min---------5mg In 1min-----------5/10=0.5mg Therefore dose of aminophylline is=0.5mg/kg/min

Exercise (Q2)..How much distilled water will be required to prepare atropine solution of 100mg/ml?Amount of atropine given is 1 gram. Amount of atropine =1g=1000mg Strength of atropine=100mg/ml 100mg of atropine in 1ml of solution 1g(1000mg) of atropin in …? 1000/100x1=10ml Therefore answer is ..10ml of distilled water

Exercise (Q3)You are provided 200mg of dopamine dissolved in 500ml of normal saline.How many drops per minutes would be to a cardiogenic shock patient weighing 60kg to maintain a dosing rate of 12mcg/kg/min.(1ml=16drops) Dosing rate 12mcg/kg/min For 60kg..Dosing rate is 12x60=720 mcg/min 200mg (200x1000mcg) of dopamine in 500ml N/S 720 mcg of dopamine in……………………..720x500/200000=1.8ml/min 1ml = 16 drops So that..1.8 ml …?..=16x1.8=28.8 drops = 29 drops/min(answer) Formula method……(mcg x kg) /25……. (12 x 60)/ 25 =28.8 drops =29 drops/min(answer)

Resources for teaching Dimensional Analysis IV Calculations site  http://www.geocities.com/Heartland/Valley/3049/iv/clcltns.html  Math tutorials  http://www.utep.edu/nurs4710/tutorials/  IV drip rate problems and dosage calculation problems  http://www.dalesplace.net/iv.htm  

Nursing Math Simplified “Math Magic” Author: Susan Garner Moore ISBN: 0-943202-22-1 53 page book – basics on what they call “Math Magic”

Quick & Easy Dosage Calculations Quick & Easy Dosage Calculations: Using Dimensional Analysis by: Christina Wu Nasrawi, Judith Ann Allender, Maura Conner   Product Details Paperback: 318 pages ; Dimensions (in inches): 0.75 x 10.00 x 8.50 Publisher: W B Saunders; 1st edition (February 15, 1999) ISBN: 0721671330

Clinical Calculation Made Easy Clinical Calculations Made Easy: Solving Problems Using Dimensional Analysis : Softbound By Gloria Craig Edition: Second ISBN: 0-7817-3099-6 Pub Date: February 2001 Pages: 272 Illustrations: 245

Medical Dosage Calculations Medical Dosage Calculations June Looby Olsen, Leon J. Ablon, Anthony P. Giangrasso, Anthony Patrick Giangrasso ISBN: 0805356053 Format: Paperback, 336pp Pub. Date: January 1995 Publisher: Benjamin-Cummings Publishing Company Edition Description: Older Edition

Dimensional Analysis for Meds Dimensional Analysis for Meds Anna M. Curren, Laurie D. Munday ISBN: 076685938X Format: Paperback, 319pp Pub. Date: November 2001 Publisher: Delmar Learning Edition Description: 2ND BK&CDR Edition Number: 2

Dosage Calculations Dosage Calculations : A Simplified Approach Billie Ann Wilson, Billie E. Wilson, With Margaret T. Shannon   ISBN: 083859297X Format: Paperback, 219pp Pub. Date: December 1996 Publisher: Appleton & Lange Edition Description: 3rd Edition Edition Number: 3

Calculating Drug Dosages Calculating Drug Dosages: An Interactive Approach to Learning Nursing Math Sandra Luz Martinez De Castillo, Sandra Luz Castillo, Maryanne Werner-McCullough ISBN: 0803605781 Format: Other Format, 128pp Pub. Date: January 2002 Publisher: Davis F A Edition Description: BK&CD-ROM Edition Number: 1

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