Question 1

AN ORDER READS 0.5 g BY MOUTH. THE PHARMACY SENDS 250 mg TABLETS. HOW MANY TABLETS DO YOU GIVE?

Accepted Answer

2 tablets. Convert first: 0.5 g is 500 mg. Then 500 mg desired divided by 250 mg per tablet gives 2 tablets. Skipping the gram-to-milligram step is the classic setup error that produces 0.002 tablets.

Question 2

TO CHANGE 2 g INTO mg, YOU MOVE THE DECIMAL POINT THREE PLACES TO THE ___.

Accepted Answer

RIGHT. Going from a larger unit (gram) to a smaller one (milligram) makes the number bigger, so 2 g becomes 2,000 mg: three places right, because there are 1,000 mg in a gram.

Question 3

A PATIENT IS ORDERED 0.125 mg OF DIGOXIN. THE TABLETS ON HAND ARE 0.25 mg EACH. WHAT DO YOU GIVE?

Accepted Answer

Half a tablet. 0.125 mg divided by 0.25 mg per tablet is 0.5, so half a tablet. The order is smaller than the tablet, which is your sense check that the answer must be under one.

Question 4

AMOXICILLIN 375 mg IS ORDERED. THE SUSPENSION ON HAND IS 250 mg PER 5 mL. HOW MANY mL DO YOU DRAW UP?

Accepted Answer

7.5 mL. Dose wanted over dose on hand times the volume it comes in: 375 divided by 250 is 1.5, and 1.5 times 5 mL is 7.5 mL. The dose is bigger than 250 mg, so the volume must be bigger than 5 mL.

Question 5

A CHILD WEIGHS 44 lb. THE ORDER IS 10 mg PER kg FOR ONE DOSE. WHAT IS THE DOSE?

Accepted Answer

200 mg. Weight-based doses use kilograms. 44 lb divided by 2.2 is 20 kg, and 20 kg times 10 mg per kg is 200 mg. Using pounds directly gives 440 mg, more than double the dose.

Question 6

1,000 mL OF NORMAL SALINE IS ORDERED OVER 8 HOURS ON AN INFUSION PUMP. WHAT RATE DO YOU SET?

Accepted Answer

125 mL/hr. Pumps run in mL per hour, so divide total volume by hours: 1,000 mL over 8 hours is 125 mL/hr. No drop factor is involved because the pump counts the volume for you.

Question 7

THE SAME 1,000 mL MUST RUN OVER 8 HOURS BY GRAVITY, USING TUBING WITH A DROP FACTOR OF 15 gtt/mL. WHAT DRIP RATE DO YOU COUNT?

Accepted Answer

31 gtt/min. Volume times drop factor over time in minutes: 1,000 times 15 is 15,000, divided by 480 minutes is 31.25, which rounds to 31 gtt/min because you cannot count part of a drop.

Question 8

THE ORDER IS 150 mcg. THE VIAL IS LABELLED 0.1 mg PER mL. HOW MANY mL DO YOU GIVE?

Accepted Answer

1.5 mL. Match units first: 150 mcg is 0.15 mg. Then 0.15 mg divided by 0.1 mg per mL is 1.5 mL. Leaving the order in micrograms gives an answer of 1,500 mL, which no injection could be.

Question 9

BEFORE USING DESIRED OVER HAVE, THE ORDERED DOSE AND THE DOSE ON HAND MUST BE IN THE SAME ___.

Accepted Answer

UNIT. The formula only cancels correctly when both doses share a unit. An order in grams and a label in milligrams has to be converted first, or the answer is off by a factor of 1,000.

Question 10

HEPARIN 1,000 units PER HOUR IS ORDERED. THE BAG HOLDS 25,000 units IN 250 mL. WHAT PUMP RATE DO YOU SET?

Accepted Answer

10 mL/hr. Find the concentration first: 25,000 units in 250 mL is 100 units per mL. Then 1,000 units per hour divided by 100 units per mL is 10 mL/hr.

Question 11

A 15 kg CHILD IS ORDERED 250 mg EVERY 8 HOURS. THE SAFE RANGE IS 20 TO 40 mg PER kg PER DAY. WHAT DO YOU DO?

Accepted Answer

Hold and clarify: 750 mg a day is above the 600 mg maximum

The safe range for 15 kg is 300 to 600 mg a day. Three doses of 250 mg add up to 750 mg a day, which is over the maximum, so the order is questioned before anything is given.

Question 12

IN DIMENSIONAL ANALYSIS, EACH CONVERSION FACTOR PUTS THE UNIT YOU WANT TO CANCEL IN THE ___.

Accepted Answer

DENOMINATOR. A unit cancels when it appears once on top and once underneath. Placing the unwanted unit underneath in the next factor removes it, leaving only the unit you want in the answer.

Question 13

WHICH OF THESE DOSES IS WRITTEN THE SAFE WAY?

Accepted Answer

0.5 mg. 0.5 mg has a leading zero, so the decimal point cannot vanish. A bare .5 can be read as 5, 5.0 can be read as 50, and U for units can be read as a zero or a four.

Dosage Calculation Conversions and Formulas