Medication Calculations Randall Stennett RN MSN Medication Calculations

Medication Calculations Randall Stennett RN, MSN

Medication Calculations • Learning objectives • You should be able to: – calculate weight in Kilograms – calculate Therapeutic dose – calculate Concentration/Dilution – calculate Rate of administration – Take the appropriate action based on your calculations

To complete this presentation you will need: • • Pencil Paper Calculator Drug references

• References • Lefever-Kee, J, and Marshall, S. M. , (2009), Clinical Calculations with Applications to General and Specialty Areas. (6 th ed. ) St. Louis: Elsevier. • Morris, D. G. , (2006). Calculate with Confidence, (4 th ed. ) St. Louis: Mosby • Gahart, B. and Nazareno, A. (2009). Intravenous Medications (23 rd ed. ) St. Louis: Mosby • Lexi-Comp Online http: //online. com/crlonline

st 1 order of business • This presentation is divided into 3 ‘sections’. • Each section will address 2 -3 topics. • The content will be reviewed during the first three weeks of class.

• Week 1 Weight in kilograms/Therapeutic dose • Week 2 Concentration/Rate of Administration • Week 3 Taking appropriate action/ Putting it all together (Multifaceted problems)

• Medication errors account for at least 7, 000 deaths in the United States each year. • Medication errors occur in nearly 1 of every 5 doses given to patients in the typical hospital. * *Barker KN, Flynn EA, Pepper GA, Ph. D, Bates DW, Mikeal RL. Medication errors observed in 36 health care facilities. Arch Intern Med 2002; 162: 1897 -1903.

Calculation Quizzes ► There will be 4 quizzes throughout the semester (each is comprehensive) ► 25 questions on each quiz ► 1 hour for each quiz ► Each question = 1 point ► Point total for all quizzes will become your 9 th theory exam and will be factored into your final theory grade

►I am available for any help you may need. ►I will be happy to work with you oneon-one, or in small groups. ►In the past, small groups, at the end of lecture periods, has worked well. ►Randall Stennett – Office 122 – Phone 797 -0955 ext 246 – Email through Scholar 360 – I will attempt to return email within 1 -2 days

Review • There are 3 ways to work your calculations – Basic Formula – Ratio and Proportion and – Fractional Equation • You, most likely have your preferred method , use what works for you! • Here is a quick review of the methods.

Review • Basic Formula (BF) D H x V = X (amount to give) D: desired dose or drug dose ordered H: on-hand (drug dose on label) V: vehicle- form and amount in which the drug comes

Review • Ratio and Proportion (RP) Known H : Desired V : : D : X means extremes • H & V – known quantities (dose on hand vehicle) • D & X – the desired dose and the unknown amount to give • Multiply the means and the extremes. • Solve for X

Review • Fractional Equation (FE) H V = D X H: dose on hand V: form in which the drug comes D: desired dosage X: the unknown amount Cross multiply and solve for X

BF: D X V H Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

BF: D X V H Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

RP: H : V : : D : X Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

RP: H : V : : D : X Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

FE: H V D X Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

FE: H V D X Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

Find the method that works for you and stick with it!

Medication Calculations Step wise approach • Weight in Kilograms • Therapeutic dose/range Ki. TCAT • Concentration/dilution • Rate of Administration • Take the appropriate action based on your calculations

A 42 pound, 6 year old patient, is to receive vancomycin (Vancocin) 382 mg IV every 12 hours. Pharmacy sends a syringe labeled: Vancomycin 380 mg in 100 ml of NS. Drug reference states: Therapeutic dose is 40 mg/kg/24 hours. Concentrations greater than 5 mg/ml are not recommended. A single pediatric dose is given over 60 minutes. The appropriate nursing action would be to A. B. C. D. administer the medication at 50 ml/hr. administer the medication at 100 ml/hr. notify the physician. notify pharmacy.

Calculate: • Weight in K ilograms • Therapeutic dose/range • Concentration/dilution • Rate of Administration • Take the appropriate action Ki. TCAT

Conversion Factors • 1 kg = 2. 2 lbs. (pounds to kg ÷ ) (kg to pounds X ) • 1 kg = 1000 mg. • 1 lb = 16 oz. • 1 tsp = 5 ml.

Weight in Kilograms • Our example: (pounds to kilograms) 42 pounds ÷ _____ = _______ kg.

Weight in Kilograms • Our example: (pounds to kilograms) 42 pounds ÷ _____ = _______ kg.

Weight in Kilograms • In the nursery, babies are weighed in grams. • Suppose our patient weighed 3000 grams, what’s the pt weight in kg? • Remember, 1 kg = 1000 grams

Weight in Kilograms • Suppose our patient weighed 3000 grams, what’s the pt weight in kg?

Weight in Kilograms • Another weight conversion that will be helpful to you is converting lb and ounces to kilograms 16 oz = 1 lb • Convert 14 lb 6 oz to kg

Weight in Kilograms • Convert 14 lb 6 oz to kg

Weight in Kilograms • You just weighed a baby at 7. 4 kg and the Mom asks you how much her child ‘really’ weighs?

Weight in Kilograms • 7. 4 kg is how many pounds and ounces?

Practice 15 pounds = _______ kg 53 pounds = _______ kg 4244 grams = ______ kg 598 grams = _______ kg 10 lb 7 oz = _______ kg 14 lb 2 oz = _______ kg 12. 8 kg = ______pounds _____ ounces Round to the nearest tenth.

Calculate: • Weight in Kilograms • T Ki. TCAT herapeutic dose/range • Concentration/dilution • Rate of Administration • Take the appropriate action

Therapeutic dose/range • In adults, therapeutic dose = ‘usual dose’ • In most adult cases, the range is already calculated

Therapeutic dose/range • What about pediatrics? – Age

• AGE • Infants have: • immature liver and kidney function • (delays metabolism & elimination). • decreased gastric emptying (<3 y. o. ) • (alters drug absorption) • lower concentration of plasma proteins • (can cause toxic effects in drugs that bind to proteins) • less total body fat & more total body water • ( lipid-soluble drugs may require lower doses and • water-soluble drugs may require larger doses)

Therapeutic dose/range – Body Mass

• BODY MASS • to maintain a desired drug concentration in individuals of various sizes, the drug dose MUST BE adjusted for body mass. • As children grow, changes in fat, muscle, body water, and organ maturity can alter pharmacokinetic effects of drugs. • This is why pediatric doses are measured in mg/kg • Let’s look at vancomycin

• What is the PEDIATRIC dose/range? • What is the THERAPEUTIC dose/range for our patient?

• What is the PEDIATRIC dose/range? • _____ mg/kg/_____ • What is the THERAPEUTIC dose/range for our 19. 1 kg patient? ______mg/24 hr

Therapeutic dose/range • What is the THERAPEUTIC RANGE? • _____ to ______ mg/kg/ ____

Therapeutic dose/range • What is the THERAPEUTIC RANGE? • _____ to ______ mg/kg/ ____

• Let’s calculate a therapeutic dose/range for our 42 pound patient • Patient weighs ______ kg, so… • ____ kg X ____ mg (min. dose) = ____ mg/day • ____ kg X ____mg (max. dose) = ____ mg/day • Therapeutic dose/range is _____ to _____ mg/DAY

• Let’s calculate a therapeutic dose/range for our 42 pound patient • Patient weighs ______ kg, so… • ____ kg X ____ mg (min. dose) = ____ mg/day • ____ kg X ____mg (max. dose) = ____ mg/day • Therapeutic dose/range is _____ to _____ mg/DAY

Triangle method Child’s wt 19. 1 kg X X 50 mg (min. ) 75 mg (max) (from drug reference) = = 955 mg 1432. 5 mg The therapeutic range is: 955 mg to 1432. 5 mg/DAY

Ki. TCAT • Methylprednisolone (Solu-Medrol) 100 mg IV as loading dose, for status asthmaticus. • Patient is 110 lbs • Is this a therapeutic dose?

Ki. TCAT K: T: • Methylprednisolone (Solu-Medrol) 100 mg IV as loading dose, for status asthmaticus. • 110 lb • Is this a therapeutic dose?

Ki. TCAT K: T: • Methylprednisolone (Solu-Medrol) 100 mg IV as loading dose, for status asthmaticus. • 110 lb • Is this a therapeutic dose?

• Penicillin G Aqueous 325, 000 units IV every 6 hours. • Patient is a 28. 5 lb, with a mild bacterial infection. • Is this a therapeutic dose?

• Penicillin G Aqueous 325, 000 units IV every 6 hours. • 28. 5 lbs K: T: • Is this a therapeutic dose?

A 42 pound, 6 year old patient, is to receive vancomycin (Vancocin) 382 mg IV every 12 hours. Calculate: Patient weight in kg = ______ kg Therapeutic dose/range = ______ mg/DAY

A 42 pound, 6 year old patient, is to receive vancomycin (Vancocin) 382 mg IV every 12 hours. Calculate: Patient weight in kg = ______ kg Therapeutic dose/range = ______ mg/DAY

• A 42 pound, 6 year old patient, is to receive vancomycin (Vancocin) 382 mg IV every 12 hours. • Our therapeutic dose/range is 764 mg/DAY • Our ordered dose is 382 mg Q 12 hours • There is one more step to know if our DOSE is therapeutic

• Therapeutic dose/range is 764 mg/DAY • Ordered dose is 382 mg Q 12 hours • The next step is to ÷ our calculated dose by the # of doses/day • 764 ÷ 2 = 382 mg every 12 hours

Calculate: • Weight in Kilograms • Therapeutic dose/range – Is the dose therapeutic? • Concentration/dilution • Rate of Administration Ki. TCAT • Take the appropriate action

Correct this formula with a single stroke 5 + 5 = 550 This ends the 1 st section.

Calculate: • Weight in Kilograms Ki. TCAT • Therapeutic dose/range • C oncentration/dilution • Rate of Administration • Take the appropriate action

Concentration/dilution • Concentration – The strength of a reconstituted medication • Dilution – The fluid added to a reconstituted medication to make it less concentrated or less strong

Concentration/dilution • Ultimately what we are looking for is how much medication (milligrams, micrograms, etc. ) is mixed in one milliliter of fluid (mg/ml, mcg/ml).

Concentration/dilution • Compare the dilution of the ordered medication with the recommended dilution in drug reference • Watch for key words: – MUST BE further diluted – MAY BE further diluted – FINAL CONCENTRATION of, or CONCENTRATION of

A 29 lb. patient is to receive 350 mg of ceftriaxone (Rocephin) IV every 12 hours for a wound infection. Ki. TCAT K: Patient weight= _____ kg T: Therapeutic dose range: _____- _____mg/DAY or Is the dose ordered therapeutic? _____- _____mg/DOSE

A 29 lb. patient is to receive 350 mg of ceftriaxone (Rocephin) IV every 12 hours for a wound infection. Ki. TCAT K: Patient weight= _____ kg T: Therapeutic dose range: _____- _____mg/DAY or Is the dose ordered therapeutic? _____- _____mg/DOSE

Pharmacy sends an IVPB labeled: Ceftriaxone 350 mg in 25 ml of D 5 W What is the concentration of our medication? Amount of drug in mg ÷ volume in ml = concentration of medication in mg/ml 350 mg ÷ 25 ml = 14 mg/ml Ki. TCAT K: 13. 2 kg T: 330 -495 mg/dose C: ____ mg/ml

Pharmacy sends an IVPB labeled: Ceftriaxone 350 mg in 25 ml of D 5 W What is the concentration of our medication? Amount of drug in mg ÷ volume in ml = concentration of medication in mg/ml 350 mg ÷ 25 ml = 14 mg/ml Ki. TCAT K: 13. 2 kg T: 330 -495 mg/dose C: ____ mg/ml

Concentration/dilution • What? ? !!

Concentration/dilution • What is the recommended concentration? • Is our medication appropriately diluted?

• Back to our original problem… Pharmacy sends an IVPB labeled: Vancomycin 382 mg in 100 ml of NS. What is the concentration of our medication? ____ Is our medication appropriately diluted? ____

• Back to our original problem… Pharmacy sends an IVPB labeled: Vancomycin 382 mg in 100 ml of NS. What is the concentration of our medication? ____ Is our medication appropriately diluted? ____

Concentration/dilution • Weight in Kilograms • Therapeutic dose/range Ki. TCAT • Concentration/dilution • – Is the concentration correct? ___ Rate of Administration • Take the appropriate action

Calculate: • Weight in Kilograms Ki. TCAT • Therapeutic dose/range • Concentration/dilution • Rate of A dministration • Take the appropriate action

Rate of Administration Volume to be infused X tubing drop factor = gtts/min infusion time in minutes Macrodrip sets drop factor will vary. Check the packaging! Microdrip infusion sets: 60 gtts = 1 ml 60 minutes = 1 hour, therefore gtts/min = ml/hour

Rate of Administration • IV injection = IV push • Intermittent IV = IVPB • Key phrase: must be equally distributed • Calculate the rate for a 25 ml IVPB of Unasyn with a microdrip set. Unasyn

Rate of Administration • IV injection = IV push • Intermittent IV = IVPB • Key phrase: must be equally distributed • Calculate the rate for a 25 ml IVPB of Unasyn with a microdrip set. Unasyn

Rate of Administration • Back to our original problem… Pharmacy sent an IVPB labeled: Vancomycin 380 mg in 100 ml of NS. • What is the recommended rate? • What is the rate of administration for our vancomycin dose?

Rate of Administration • Back to our original problem… Pharmacy sent an IVPB labeled: Vancomycin 380 mg in 100 ml of NS. • What is the recommended rate? • What is the rate of administration for our vancomycin dose?

Calculate: • Weight in Kilograms Ki. TCAT • Therapeutic dose/range • Concentration/dilution • Rate of Administration • Is the rate of administration ok? ___ • Take the appropriate action

This ends the 2 nd section.

Calculate: • Weight in Kilograms Ki. TCAT • Therapeutic dose/range • Concentration/dilution • Rate of Administration • T ake the appropriate action

Take the appropriate action Perform your calculations, then answer these questions… Is the dose ordered therapeutic? Is the concentration correct? Is the rate correct? Are you really ready to administer that medication?

Are you really ready to administer that medication? • Check for any – Warnings – Precautions – Contraindications

A 42 pound, 6 year old patient, is to receive vancomycin (Vancocin) 380 mg IV every 12 hours. Pharmacy sends an IVPB labeled: Vancomycin 380 mg in 100 ml of NS. Drug reference states: Therapeutic dose is 40 mg/kg/24 hours. Concentrations greater than 5 mg/ml are not recommended. A single pediatric dose is given over 60 minutes.

Putting it all together • These problems will help reinforce previous work and also illustrate some issues that are unique to pediatrics. • Work these problems on your own and we will go thru them in class.

A 97 pound, 11 year old with a diagnosis of osteomyelitis, is ordered to receive Nafcillin 800 mg IV every 4 hours. The most appropriate nursing action would be to: A. notify the physician of an incorrect dose. B. notify pharmacy of an incorrect concentration C. administer the medication by IV pump at 50 ml/hour. D. administer the medication by IV pump at 100 ml/hour.

K: T: C: A: T: A 97 pound, 11 year old with a diagnosis of osteomyelitis, is ordered to receive Nafcillin 800 mg IV every 4 hours.

• A 28 year old is diagnosed with a complicated urinary tract infection. Levofloxacin (Levequin) 250 mg IV daily is ordered. IV label reads: Levofloxacin 250 mg in 50 ml of Normal saline. Administer at a rate of 100 ml/hr. The most appropriate action would be to A. Notify the physician of an incorrect dosage. B. Notify pharmacy of concentration. C. Notify pharmacy of incorrect rate. D. Administer the medication at 25 ml/hour.

K: T: C: A: T: • A 28 year old is diagnosed with a complicated urinary tract infection. Levofloxacin (Levequin) 250 mg IV daily is ordered. • IV label reads: Levofloxacin 250 mg in 50 ml of Normal saline. Administer at a rate of 100 ml/hr.

My baby weighs 22 pounds and usually takes ¾ teaspoon of Tylenol elixir, but it doesn’t seem to be working. What should I do? Tylenol elixir 120 mg/5 ml The most appropriate answer would be A. “ Give your baby 1 teaspoon of Tylenol every 4 -6 hours. ” B. “ Give your baby 2 teaspoons of Tylenol every 4 -6 hours. ” C. “Try giving some Motrin now. ”

K: T: C: A: T: • My baby weighs 22 pounds and usually takes ¾ teaspoon of Tylenol elixir, but it doesn’t seem to be working. What should I do? • Tylenol elixir 120 mg/5 ml

The order for a 14 pound infant reads: 2. 5 ml of Tylenol with Codeine elixir every 4 hours prn for pain. Is this a therapeutic dose?

K: T: C: A: T: • The order for a 14 pound infant reads: 2. 5 ml of Tylenol with Codeine elixir every 4 hours prn for pain. • Is this a therapeutic dose?

Bactrim (sulfamethoxazole/trimethoprim) 7. 5 ml orally every 12 hours has been ordered for a 32 pound, 18 month old. Drug reference states the usual pediatric dose is 6 -12 mg of the trimethoprim component/kg/day, given every 12 hours. Medication label reads: Bactrim (sulfamethoxazole 200 mg/ trimethoprim 40 mg/5 ml) The most appropriate action would be to A. administer 7. 5 ml every 12 hours. B. administer 3. 75 ml every 12 hours. C. notify the physician of an inappropriate dose. D. request the tablet form due to the volume required for therapeutic dose.