© 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill Math and Dosage Calculations for Health Care Third Edition Booth & Whaley Chapter

© 2010 The McGraw-Hill Companies, Inc. All rights reservedMcGraw-Hill

Math and Dosage Calculations for Health Care Third Edition

Booth & Whaley

Chapter 11: Calculations for Special Populations

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Learning Outcomes

11.1 Explain why dosages for special populations must be based on theindividual patient.

11.2 Identify factors that affect the absorption, distribution,biotransformation, and elimination

of drugs in special populations.

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11.3 Determine safe doses for special populations.

11.4 Calculate patient dosages based on body weight.

11.5 Find a patient’s body surface area (BSA).

Learning Outcomes (cont.)

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11.6 Calculate patient dosages based on a patient’s BSA.

11.7 Describe volume and medication limitations for special populations.

11.8 Calculate infusion rates based upon body weight.

Learning Outcomes (cont.)

11-4


Introduction

Two populations requiring extra consideration when calculating medication dosages Pediatric (less than 18 years old) Geriatric (over 65 years old)

Risk of harm is far greater due to the way they break down and absorb medications.

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Introduction (cont.)

Clarify all confusing drug orders

Calculate with absolute accuracy

Verify that dose is safeSeek assistance from your

supervisor

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Do not take short cuts with medication calculations.

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Factors That Impact DosingStandardized doses based on

assumptions The patient’s body and age Body systems are fully developed and

functioning

Assumptions do not hold true for all populations or situations

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Factors That Impact Dosing – PHARMACOKINETICS

Study of how drugs are used by the body Absorption Distribution Biotransformation Elimination

Understanding these processes allows for adjustments for special populations

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Factors That Impact Dosing – PHARMACOKINETICS (cont.)

Absorption Process that moves a drug from the

site where it is given into the bloodstream

IV medications bypass the absorption process

Oral medications – digestive system

Topical – through the skin

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Distribution Process that moves the drug from the

bloodstream to other body compartments

Target site – where the drug produces its desired effect

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Biotransformation Process that chemically changes the

drug in the body

Occurs primarily in the liver

Helps to protect the body from foreign chemicals including drugs

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Elimination Process where the drug leaves the

body Main route – urine Other ways

Air that we exhaleSweatFecesBreast milkOther body secretions

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Adjust dose If one of the four processes are not

functioning within certain limits

Made according to nature and severity of patient’s condition

May by higher or lower than standard doses

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Factors That Impact Dosing (cont.)

Conditions that impact dosing Stomach or intestinal disorders Liver disorders Obesity Kidney disease

Functions of body systems change over the life of a person.

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Factors That Impact Dosing (cont.)

Newborns – systems not fully developed pH of stomach is

lower Thinner skin Liver still

developing Less circulation to

muscles

Geriatrics – systems deteriorate Skin and veins

become fragile Decreased liver

function Decreased kidney

function Poor circulation

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Working with Special Populations

Other Considerations Parent or caretaker may be

administering or assisting with medications.

Educate regarding medications

Geriatric patients may have decreased awareness or understanding.

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Working with Special Populations – GERIATRIC PATIENTS

Show respect

Listen to their concerns

Encourage them to Use the same pharmacy to fill all

prescriptions Have one primary care physician to monitor

and approve all medications Keep a list of all medications

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Special Populations – GERIATRIC PATIENTS (cont.)

Decreased dexterity Injections Eye drops Open bottles

Difficulty swallowing Drugs that cannot be crushed Foods that can be mixed with drugs

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Hearing loss Do they understand instructions? Have them repeat information back to

you

Difficulty reading small print Labeling Tablet colors

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Short-term memory loss Written instructions Medication calendars Pill dispensers

Avoid OTC or herbal meds until discussing with physician.

Do not take expired meds or borrowed meds.

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Teaching Patients About Medications

1. Name of the medication

2. Purpose

3. How to store it

4. How long to take the medication

5. How and when to take it

6. How to know if it is effective

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Teaching Patients About Medications (cont.)

7. Required follow-up tests, doctor appointments

8. Possible side effects and what to do

9. Interactions with other drugs and foods

10. Symptoms to report to the doctor

11. What to do if a dose is missed

12. Keeping a list of all medications

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Dosages Based on Body Weight

Amount of medication per

Weight of the patient per

Unit of time

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Dosages Based on Body Weight

Rule 11-1Rule 11-1 Calculating dosage based on body weight:

1. Convert the patient’s weight to kilograms

2. Calculate the desired dose D by multiplying dose ordered by the weight in kilograms such as

dose desired kg or dose desired kg xkg

mcgx

kg

mg

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Dosages Based on Body Weight (cont.)

Rule 11-1Rule 11-1 (cont.)

3. Confirm whether or not the desired dose is safe by checking the label, package insert, or product literature.

4. Calculate the amount to administer, using fraction proportion, ratio proportion, dimensional analysis, or the formula method.

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Calculate the amount to administerto a 3-year-old weighing 34 lb.

Ordered: hysocyamine sulfate 5 mcg/kg subq 1 h pre-anesthesiaOn hand: hysocyamine sulfate 0.5 mg/mL

Convert 34 lb to kg = 15.5 kg

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Example Example

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Find the desired dose:

77.5 mcg = D

Find the amount to administer:77.5 mcg = 0.0775 = 0.08 mg

Amount to administer =

0.16 mL

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Example (cont.) Example (cont.)

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Pediatric InjectionsStage of Development Maximum Volumes for

IM Injections

Infant 0.5 – 1 mL

Toddler, walking for at least 1 year

1 mL

Preschooler/elementary school age

1 – 1.5 mL

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Ensuring Safe Dosages

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Ensuring Safe Dosages (cont.)

Rule 11-2Rule 11-2 Ensuring Safe Dosages

When working with special populations, always check the package insert, drug label, or product literature to ensure the safety of the dose to be administered.

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Error Alert !

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Error Alert !Weight 8 lb 6 oz Convert 6 ounces to pounds

using as the conversion

Therefore 8 lb 6 oz = 8.375 lb

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Practice

Determine whether the following order is safe. If safe, calculate the amount to administer.

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Patient: Child who weighs 14.5 kgOrdered: Amoxil 75 mg PO q8hOn hand: Usual child dose 20-40 mg/kg day q8h

Answer Dosage doesn’t fall within recommended dosage range; contact the physician.

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Dosages Based on Body Surface Area (BSA)

BSA calculations

Provide more accurate dosage calculations that are specific to the patient’s size and severity of his/her illness.

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Dosages Based on BSA – CALCULATING BSA

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Dosages Based on BSA – CALCULATING BSA (cont.)

Rule 11-3 Rule 11-3 Calculating the BSA using a formula:

1. If you know the height in cm and weight in kg, calculate

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Rule 11-3 Rule 11-3 (cont.)

2. If you know the height in inches and weight in pounds, calculate

If the result is less then one, round to nearest hundredth.

If the result is greater than one, round to nearest tenth.

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Find the body surface area for an adult who is 5’6” talland who weighs 168 lb.

BSA = 1.88 m2

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Example Example

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Rule 11-4 Rule 11-4 Calculating BSA using a Nomogram:

Using a straight edge, align the straight edge so it intersects at the height and weight.

Doing so will create an intersection in the BSA scale.

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Find the body surface for a baby who is 24 in and weighs 14 lb and 8 oz.

Use the “Child’s Nomogram”

BSA = 0.21 m2

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Example Example

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Calculating Dosage Based on BSA

Rule 11-5 Rule 11-5 Calculating dosage based on BSA:1. Calculate the patient’s BSA.

2. Calculate the desired dose:

dosage ordered per m2 x BSA = desired dose

3. Confirm whether the desired dose is safe.

4. Calculate the amount to administer, using fraction proportion, ratio proportion, or the formula method.

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Calculating Dosage Based on BSA (cont.)

Ordered: CeeNU (1st dose) 140 mg now for a child 38 in tall and

weighing 47 lbAccording to the package the first dose is a single

oral dose providing 130 mg/m2 .

BSA = 0.76 m2

Desired dose should be 98.8 mg (based on recommended dosing)

Ordered dose of 140 mg is too large for the patient.

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Example Example

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PracticePatient: 34 cm tall, 5 kgOrdered: Cerubidine 5.5 mg IV weeklyOn hand: Cerubidine injection 5mg/mL when

reconstituted Recommended pediatric dose 25 mg/m2

If dose is safe, calculate amount to administer:

BSA = 0.22 m2 Desired dose = 5.5 mg

Dose ordered is a safe dose

Amount to administer = 1.1 mL

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Daily Maintenance Fluid Needs (DMFN)

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Daily Maintenance Fluid Needs (DMFN)(cont.)

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Daily Maintenance Fluid Needs (DMFN) (cont.)

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Amount of maintenance fluid required varies by weight

Replacement fluids Based on patient’s condition

VomitingDiarrheaFever

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Rule 11-6 Rule 11-6 To calculate daily maintenance fluid needs (DMFN) based on weight:

1. If the patient weighs up to 10 kg, find

2. If the patient weighs 10 to 20 kg, find

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Rule 11-6Rule 11-6(cont.)

3. If the patient weighs over 20 kg, find

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Find the DMFN for

a patient weighing 16 kg.

DMFN mL =

DMFN mL = 1000 + 300

DMFN mL = 1300 mL

Find the DMFN for a patient weighing 24 kg.

DMFN mL =

DMFN mL = 1500 + 80

DMFN mL = 1580 mL

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Examples Examples

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Rule 11-7Rule 11-7For pediatric patients and critically ill patients, the amount of solution in the IV tubing must be considered when determining infusion times and volumes.

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Standard IV tubing contains 10 mL of solution per five feet. When using a volume control chamber

and standard tubing, medication will not reach patient until this 10 mL infuses.

Low-volume tubing contains only 0.3 mL of solution per five feet.

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Practice Mrs. Robin had an oral intake of 750 mL. She

weighs 145 lb How much more is required for the patient’s DMFN?

Convert wt to kg: 65.9 kg = 66 kg

DMFN = = 2420mL

2420 mL – 750 mL = 1670 mL

She requires 1670 mL to meet her DMFN.

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Creatinine Clearance

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Creatinine Clearance (cont.)

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Diseases that can damage kidneys Hypertension Diabetes Congestive heart failure

Drugs that alter or change kidney function Lasix Aminoglycoside antibiotics

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Ideal and Actual Body Weight Geriatric patients – decreased proportion

of lean body mass and water Alters distribution of drugs Monitor serum drug levels

Some water-soluble drugs strongly bound to lean tissue

Fat-soluble drugs distributed to body fat Slower release into circulation Residual effects

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Ideal and Actual Body Weight (cont.)

Water soluble drug doses for Overweight patients – based on ideal

body weight

Underweight patients (below ideal body weight) – based on actual weight

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Ideal and Actual Body Weight (cont.)

Rule 11-8 Rule 11-8 Determining safe dosages for geriatric patientsCheck the package insert or product literature and check if dose ordered is safe based on renal function and ideal or actual patient weight.

If the dose is safe, calculate the amount to administer.

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Determine Safe Dosages for Geriatric Patients

A 78-year-old male is 5’4” tall and weighs 180 lb. (Ideal weight range is

122–157 lb.) He has normal renal function and has a nonlife-threatening infection.

Ordered: Garamycin 85 mg IM q 8hOn hand: Garamycin injection, 40 mg/mL (usual

dosage is 1 mg/kg)

Convert ideal body weight to kg: 55 to 71 kg

Safe dosage range = 55 mg to 71 mg

85 mg does not fall within this range.

Contact the physician.

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Example Example

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Error Alert!

For medications that are strongly bound to lean body tissue, calculate an overweight patient’s dose on ideal body weight, not actual weight.

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PracticeMr. Adams weights 172 lb (at ideal body weight). He

is 5 ft, 7 in tall. CLCR 60 mL/min

Ordered: Vancocin HCl 150 mg IV q6hDaily recommended dosage for patients with normal

renal function 2g in divided doses. Recommended daily dose for patients with creatinine clearance of 60 mL/min is 925 mg/24 h.

Is dose ordered safe?

Yes 600 mg/24 h, which is less than 925 mg/24 h

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Polypharmacy

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Drug Interactions

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Drug Interactions (cont.)

Rule 11-9Rule 11-9 To identify cases of polypharmacy and reduce the risk of drug interactions, ask elderly patients about:

1. All medications they take which are prescribed by either their primary physician or specialists

2. Any over-the-counter medications they take

3. Any social drugs which they use

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Rule 11-9 Rule 11-9 (cont.)

4. Medications that they borrow from family and friends

5. Herbal and home remedies that they use

6. Bringing all medications they take to be checked.

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Factors causing adverse drug reactions Advanced age

Small body size

Multiple illnesses

Multiple medications

Living alone

Malnutrition

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Drugs to Avoid in Specific Diseases

Severe Risk Drugs

Benign prostatic hypertrophy

Antihistamines, anti-Parkinson’s drugs, GI antispasmodics, antidepressants

Cardiac dysrhythmia Tricyclic antidepressants

Clotting disorders Antiplatelet drugs, aspirin

COPD Hypnotics, sedatives, beta blockers

GI diseases NSAIDs, aspirin

Seizures Metoclopramide (Reglan)

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Drugs to Avoid in Specific Diseases

Less Severe Risk Drugs

Benign prostatic hypertrophy

Narcotics

ConstipationAntihistamines, anti-Parkinson’s drugs, GI antispasmodics, antidepressants

Diabetes mellitus Steroids, beta blockers

GI diseases Aspirin, potassium supplements

Insomnia Decongestants, bronchodilators, some antidepressants

Seizures Antipsychotics

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Apply Your Knowledge

True or FalseA baby who weighs 6 lb 8 oz weighs

6.8 lb.

A baby who weighs 9.5 lb weighs 9 lb 8 oz.

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Answer False

Answer True

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What are three resources you can consult to see if the calculated dose is a safe dose to administer?

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Answer 1. Drug label2. Package insert3. Drug literature

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Pediatric dosages should be rounded to the nearest: a. Tenthb. Hundredthc. Thousandth

What two things are pediatric dosages often based on?

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Answer Weight and BSA

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Answer

Daily maintenance fluid needs (DMFN)

What is the amount of fluid the patient needs over a 24-hour period called?

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Which age-related change would indicate a need to consider a smaller needle length for an IM injection?a. thinner, more fragile skinb. loss of subcutaneous tissuec. decreased muscle massd. difficulty swallowing

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The test used to measure the rate at which the kidneys filter the blood is called:a. kidney function test creatinineb. renal function testc. creatinined. creatinine clearance

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True or FalseFor medications that are strongly bound to lean body tissue, calculate an overweight patient’s dose on the ideal weight, not actual weight.

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Answer True

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Polypharmacy occurs when a patient:

a. uses too many pharmacists

b. takes many medications at a time

c. borrows a medication from a friend

d. sees only one physician

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End of Chapter 11

Perfection consists not in doing extraordinary things, but in doing ordinary things extraordinarily well.

~Angelique Arnauld

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© 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill Math and Dosage Calculations for Health Care Third Edition Booth & Whaley Chapter