dosage problems

• Dosage Problem

• D = S X O (Dosage = Supply X Order)

1. The doctor orders Amoxicillin 750 mg PO q 12 h. The stock supply (dose on hand) is Amoxicillin 250 mg/tab.

a. How many tablets will you give for the correct dose?

what equation will i use?

• D = S X O (Dosage = Supply X Order)

1. The doctor orders Aldomet 11 mg/kg/day in equally divided doses      q l2h. The dose on hand is 125 mg tablets. The patient weighs 98 lbs.

a. How many tablets will you administer for one dose? (Answer: 2 tabs)

what equation will i use?

• D = S X O (Dosage = Supply X Order)

Reconstitution

R= S X O (Reconstitution equals Supply times Order)

Supply is written as the yield.

•  (A vial with 1 g of drug is reconstituted with 4.9 mL of NS to yield 200 mg/1 mL.

Reconstitution

what is the supply stock?

• The supply is 200 mg/1 mL.

• The 1 g and the 4.9 mL added to the vial are extra information.)

1. The doctor orders Chloromycetin 0.5 gram to be added to 100 mL D-5-W IVPB to infuse over 30 minutes q 8h. The stock supply is a 4 g vial. Directions say to reconstitute with 9.8 mL of sterile water to yield 10 mL.

a. How many mL will you add to the IVPB for the correct dose? (Answer: 1.3 mL)

what equation is this?

• R= S X O (Reconstitution equals Supply times Order)

IV Flow Rates for the main IV

equation

• mL/h = iv/it (infusion volume divided by infusion time)

• gtt/min = DF X (iv/it) (Drop factor times [infusion volume/infusion time])

ROUND TO THE WHOLE #

1. The doctor orders 1000 mL D-5- W IV q 6h. The drop factor is 15 gtt/mL.

a. Calculate the flow rate in mL/h. (Answer: 167 mL/h

b. Calculate the flow rate in gtt/min. (Answer: 42 gtt/min)

What equation is this?

• mL/h = iv/it (infusion volume divided by infusion time)

• gtt/min = DF X (iv/it) (Drop factor times [infusion volume/infusion time])

IVPB Flow Rates

equation

• makes sure you use volume and time for the IVPB and not for the main/primary IV

  • mL/h = iv/it (infusion volume divided by infusion time)

  • gtt/min = DF X (iv/it) (Drop factor times [infusion volume/infusion time])

1. The doctor orders 1000 mL D-5-W IV q8h. The doctor orders Ceptaz 20 mg/kg to be added to 100 mL NS to infuse over 45 minutes q 6h. The stock supply of Ceptaz is a 1 g vial. The directions say to reconstitute with 4.8 mL of sterile water to yield a concentration of 200 mg/mL. The patient weighs 165 lbs. The drop factor is 20 gtt/mL.

1. Calculate the flow rate of the IVPB in gtt/min. (Answer: 44 gtt/min)

what’s the equation?

• gtt/min = DF X (iv/it) (Drop factor times [infusion volume/infusion time])

• Putting It All Together

• First, what is the question asking?

• Second, go to the order.

• Third, is there something memorized from the Dosage Table that you can use to convert from the unit given (order) to the unit asked for in the question?

. The doctor orders KC1 30 mEq to be added to 1000 mL D-5-W IV to infuse at 60 mL/h. The stock supply is 2 mEq/mL The drop factor is 15 gtt/mL.

a. How many milliliters of the drug will you add to the IV for the correct dose? (Answer: 15 mL)

b. Calculate the flow rate of the IV in gtt/minute. (Answer: 15 gtt/min)

what equation

a- Ml/ dose

b- drop factor x iv/ it

Special IV Flow Rates

mL/h = S X O

gtt/min = DF X S X O

RUZ

rounding

• Round IV flow rates (mL/h and gtt/min) to the whole number

  • 41.66666 mL/h → 42 mL/h

  • 33.33333 gtt/min → 33 gtt/min

• Round all other types of problems to the tenths place

  • 1.42 mL/dose → 1.4 mL/dose

  • 3.56 mL/dose → 3.6 mL/dose

RUZ

 Units

• Correct Units are a must! Answers are incorrect if the unit is incorrect.

RUZ

zero rules

• No trailing zeros (if the answer is 2, do not put 2.0)

• Always use a leading zero if the answer is less than 1 (if the answer is .2, you must put 0.2)

Supply

• What is available for the order to be given from

• May also be called stock supply, dose on hand, strength, yield 

• Must have drug amount and the drug form (5 mg/1 mL = 5 mg of drug per 1 mL of liquid; 500 mg/tab = 500 mg of drug per 1 tablet)

• Rounding to the tenths place

• For example:  1.36

• Since that number is 5 or higher, the number in the tenths place (3) rounds up to 4. 

• Rounding 1.36 to the tenths place = 1.4

• Rounding to the whole number

•  If that number is 5 or higher, then the number to the left of the decimal rounds up. 

• For example:  26.8

• That number is 8. Because that number is 5 or higher, the number to the left of the decimal (6) rounds up to 7. 

• Rounding 26.8 to the whole number = 27

• Rounding to the whole number

• #2

• Another example:  9.4

• That number is 4. Because that number is less than 5, the number to the left of the decimal point (9) remains the same and is not rounded up, and the decimal is dropped. 

• Rounding 9.4 to the whole number = 9