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Introduction to Medication Calculation

Student Success Immersion ProgramUniversity of Maryland, School of Nursing

Presentation created by Amanda Pfaff, RN, BSN

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Objectives Introduce different forms of medication

administration

Reading a drug label

Required conversion factors

Types of medication calculation

Rounding rules

Dimensional Analysis

Why is it important?Medication administration is one of the chief

responsibilities of a nurse

Nurses are often the “last line of defense”

Solid knowledge base helps prevent errors

Do Not Panic!

This is an introduction

You are not expected to know this material at this time

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Different Types of Medication

Oral Medications Supplied in a variety of forms Tablets are the most common If patient has difficulty swallowing some tablets

can be broken, crushed, or capsules can be opened

Enteric coated and sustained/extended release should NEVER be crush

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Oral Medications cont.Oral medications may also come in liquid form

Elixirs and oral suspension

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Parenteral MedicationsParenteral: Outside the GI tract

Given when they can’t be given orally or when a rapid onset is desired

Absorbed directly in the bloodstream

Parenteral RoutesSubcutaneous Injection: Beneath the skin, in fat

Intramuscular Injection (IM): in the muscle

Intradermal Injection: within the skin

Intravenously (IV): within the vein

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Parenteral FormsSupplied as a liquid or as a powder that needs

to be reconstituted

Ampules: single dose containers, need to be broken, made of glass

Vials: Glass or plastic container that is sealed with rubber stopper Vials often contain more than 1 dose of the

medication

Reconstitution Some drugs are unstable

in liquid form and must be in powder form until they are ready for use

Reconstituted: Dissolved with sterile diluents

Common Diluents: sterile water, sterile normal saline (NS), and 5% dextrose solution (D5W)

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Parenteral Forms

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IV AdministrationGravity infusion

Infusion pumps

IV push (IVP)

IV Piggybacks (secondary infusions)- medications infused in addition to regular IV fluids, smaller amount

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IV Administration

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IV AdministrationIV drip

(via gravity or infusion pump)

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Why do you need to round to a whole number?

IV Administration

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Why don’t you need to round to a whole number?

IV Push

Reading a Drug Label

1. Brand name2. Generic name3. Dose4. Manufacturer

5. Expiration

6. Safety warnings7. Form

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7

MeasurementsMetric System is system of choice

All answers expressed as decimals NOT fractions

More accurate and simplistic

Measurement Conversions1000 ml = 1 L

5 ml = 1 tsp

15 ml = 1 Tbsp

3 tsp = 1 Tbsp

30 ml = 1 oz

240 ml = 1 cup

8 oz = 1 cup

• 1000 mcg = 1 mg

• 1000 mg = 1 g

• 2.2 lb = 1 kg

At the time of your test it is expected that you will have these conversions memorized.

Common Metric Measures – Practice

Convert the following: 1 g = ____ mg

0.015 g = ____mg 750 mg = _____ g 0.5 L = ____ mL

0.0004 g = _____ mg 1.2 g = _____ mg

0.008 g = ____ mg

Common Metric Measures – Practice Answers

Convert the following: 1 g = 1000 mg

0.015 g = 15mg 750 mg = 0.75g 0.5 L = 500 mL

0.0004 gm = 0.4 mg 1.2 g = 1200 mg 0.008 g = 8 mg

Common Metric Measures – Practice

1. Convert 1.5 oz. into an equal volume of tablespoons (Tbsp.).

2. A patient weighs 154 lbs. What is this patient’s weight in kilograms?

3. The doctor instructed Bob to take 1 tablespoons of cough syrup every 12 hours. Bob only has teaspoons available to measure with. How many teaspoons should he take for each dose?

4. There are 2 bottles of milk of magnesia on the shelf at the pharmacy. One contains 10 oz. and the other has 300 mL. Which has the larger volume?

Common Metric Measures – Practice- Answers

1. 3 Tbsp.2. 70 kg3. 3 tsp.4. They are equal.

UnitsSome medications are measured in units

Common medications in units are: Heparin, Insulin, Epogen, Penicillin

Only insulin is measured and given in insulin syringes

Most other medications can be given in syringes marked in milliliters

Important to understand difference between units and other units of measure

Unit Syringes

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Pediatric Dosages Children differ from adults because of their weight,

height, metabolism of drugs, and immature body systems

Medications are calculated using the child or infant’s weight

Weight is always in kilograms

You will not be expected to do pediatric dosing in your first semester

Daily Dose Ranges Many drugs have “do not exceed” or “maximum doses”

given in a range

The nurse and/or pharmacist must calculate the high and low end of the range to determine accuracy

Any dose outside the therapeutic range is unsafe whether it is to high or to low.

Example: Vancomycin is unsafe to the kidneys if too high but ineffective against infection if too low.

Rounding BasicsRound up to the next highest number if

the digit to the right of the decimal is ≥ 5

The number stays the same if the digit to the right of the decimal is < 5

Rounding RulesRound all IV drip rates to a whole number

(by gravity or infusion pump)

• Round all other answers to the nearest tenth(includes IV push)

*If the question involves Kg, round Kg’s 1st, then continue problem with rounded weight. Round other calculations at the end of the problem.

Rounding examples2.667 = 2.7 (rounded up)

2.444 = 2.4 (stays the same)

3.579 = 3.6 (rounded up)

1.2214 = 1.2 (stays the same)

Rounding to the whole number

Same rules apply

Examples:

1.5666 = 2 (rounded up)

2.4566 = 2 (stays the same)

3.0999 = 3 (stays the same)

4.9010 = 5 (rounded up)

Dimensional AnalysisA format for setting up problems

Advantage: Only need one equation to set up ANY problem

Similar to Algebra!

Dimensional Analysis

• Place what you are solving for to the left of the equal sign

• To the right of the equal sign set up your equation• First numerator is information you have

about what you are solving for• First denominator is information you have

that relates to the first numerator• Unit of measure for second numerator is the

unit of measure for the first denominator

Example of Dimensional Analysis

The NP orders Augmentin 500mg PO daily. The drug arrives from pharmacy in 250mg tablets. How many tablets will you administer?

Solving for tablets.

= x

= x

= 2 tablets

Example of Dimensional Analysis

The physician orders quinidine 0.6 g PO q 4 hr. Quinidine is supplied in 200 mg tablets.

(A) How many tablets will you give for one dose? (B) How many tablets will you give in 24 hours?

Part A

= xx

= xx

= 3

Give 3 tablets for one dose

Part B

= x

You will give 18 tablets in 24 hrs

Infusion Pump RatesAlways mL/hr

x

x

=

Calculating Gravity Drip Rates

x x

x x

=

Always gtt/min

Advice for Medication Calculation

Make sure you are answering what the question is ASKING

Evaluate your own learning style and do what works best for you

Choose a method which you can do consistently and accurately

• When asked if a dose is safe, remember that going under AND going over a dose range is UNSAFE!

• You have to round IV drips to the whole number, you can’t calibrate ½ of a drop!

Remember: CONVERT, CALCULATE, AND MOST IMPORTANTLY…..CRITICALLY THINK (Does your answer make sense?)

Practice Makes PerfectMedication calculation is a skill

Don’t get frustrated

Math with a purpose (Patient safety!)

Questions?

Lets practice!