PTCB Practice Question

A prescription is written for a hydrocortisone 5% in zinc oxide compound. The total quantity to be dispensed is 50 g. On stock you have 50 mg of hydrocortisone tablets.

How many hydrocortisone 50 mg tablets will you need to triturate for this compound?

The answer is 50 tablets, but what is the formula you use to get the answer on these problems?

Thanks!

Comments for PTCB Practice Question

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Answer
by: Anonymous



The correct answer is 1000 tablets. Double check to see if that's one of the answer choices.

MATH:

You need to dispense 50g of hydrocortisone. There are 50,000mg in 50g. In stock, one tablet has 50mg. 50,000mg ÷ 50mg = 1,000 tablets.

1(tab)/50mg = x(tab)/50,000mg
1*50,000 = x*50
50,000 = x50
50,000 ÷ 50 = x50 ÷ 50
1,000 = x

You need 1,000 tablets

CHECK YOUR WORK:
50,000mg ÷ 1,000tab = 50mg per tablet

50,000 = 50g

the answer is 50 tablets
by: NY

The answer is 50 tab.
The amount of hydrocortisone in 5% zinc oxide compound 50g is 2.5g.
(5g:100g=2.5g:50g or 50gx0.05=2.5g)
2.5g=2500mg
2500mg/50mg=50


isn't the answer 100 tablets?
by: Anonymous

In sorry but isn't the prescription asking for 5% hydrocortisone to be added to the zinc compound and that the total weight would be 50g. So wouldn't the answer be 100 tablets?

2nd answer is correct
by: Dang

Answer 2 is correct, because it is asking for 5% of hydrocortisone inside a 50g compound of both zinc and hydrocortisone therefore 50g x 5% = 2.5g

First things first
by: Kathryn

In EVERY mathematical equation the FIRST thing you do is get all your UNITS OF MEASURE to be the same for all numbers given. THEN proceed with the calculations. It is UNWISE to wait till the end of your calculations to convert.

Find the units that the medication is given in that you will be needing, and use that as your standard. In this case the tabs are in mg so convert the ointment mass from grams to mg, before anything else!

ALWAYS write your units in every calculation so you know your answer is correct. Units cross multiply just like numbers. Learn how to do stoichiometry. Set up all your calculations as multiplications with units of conversion and you will never be wrong.

50g ointment = 50000mg ointment
5% hydrocort/ointment = .05 hydro/ointment

Calculation:

A. 0.05(hydro/ointment) × 50000mg(ointment) = 2500mg of hydrocortisone

(Notice the ointment units cancelled out to leave me with just the units mg, and hydrocortisone so I know my answer is correct.

B. 2500mg hydro × 1tab/50mg hydro = 50tabs

(Notice mg and hydro were both in the numerator and denominator so they cancelled out to leave the unit "tab")

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