Calculation Question

[khydroxide]

I am having trouble understanding e-value. This came from my kaplan review book. Seems pretty easy but I can't really understand how they came up with the answer.

How many grams of NaCl are needed for the following Rx. the E-value of phenylephrine is 0.32 . The Pharmacist obtains the chemical by dilution of a 1% isotonic phenylephrine solution.)

Rx:

phenylephrine 0.5%-30mL
Make isotonic with NaCl.


so here's what I did.
.5% x 30= 150mg x .32 = 48
.9% x 30 = 270mg
270 - 48 = 222 (my answer)

Correct answer is 135. I really hope someone could please explain this to me. Thanks.

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[ancienbon]

Here is how i solved it.. It says that the 1 % is isotonic so we would need 0.9/100X30= 0.27 g or 270 mg. so half percent of that solution would require 270/2 = 135 mg .

I am having trouble understanding e-value. This came from my kaplan review book. Seems pretty easy but I can't really understand how they came up with the answer.

How many grams of NaCl are needed for the following Rx. the E-value of phenylephrine is 0.32 . The Pharmacist obtains the chemical by dilution of a 1% isotonic phenylephrine solution.)

Rx:

phenylephrine 0.5%-30mL
Make isotonic with NaCl.


so here's what I did.
.5% x 30= 150mg x .32 = 48
.9% x 30 = 270mg
270 - 48 = 222 (my answer)

Correct answer is 135. I really hope someone could please explain this to me. Thanks.

 

[PTMDK]

I am having trouble understanding e-value. This came from my kaplan review book. Seems pretty easy but I can't really understand how they came up with the answer.

How many grams of NaCl are needed for the following Rx. the E-value of phenylephrine is 0.32 . The Pharmacist obtains the chemical by dilution of a 1% isotonic phenylephrine solution.)

Rx:

phenylephrine 0.5%-30mL
Make isotonic with NaCl.


so here's what I did.
.5% x 30= 150mg x .32 = 48
.9% x 30 = 270mg
270 - 48 = 222 (my answer)

Correct answer is 135. I really hope someone could please explain this to me. Thanks.

another way to interpret the question: I. phenylepi needed: 0.5% x 30ml = 150mg/1% = 15ml (15ml will be drawn from 1% isotonic phenylepi) -- since 1% phenylepi is already isotonic ==> no need to use E-value II. 30ml - 15ml = 15ml --> will need only 15ml of NS to make total 30ml soln 15ml x 0.9/100 = 135mg best rgds

 

[aboveliquidice]

I am having trouble understanding e-value. This came from my kaplan review book. Seems pretty easy but I can't really understand how they came up with the answer.

How many grams of NaCl are needed for the following Rx. the E-value of phenylephrine is 0.32 . The Pharmacist obtains the chemical by dilution of a 1% isotonic phenylephrine solution.)

Rx:

phenylephrine 0.5%-30mL
Make isotonic with NaCl.


so here's what I did.
.5% x 30= 150mg x .32 = 48
.9% x 30 = 270mg
270 - 48 = 222 (my answer)

Correct answer is 135. I really hope someone could please explain this to me. Thanks.

E value questions are 4 steps.

1 - Calculate how much total drug is present
2 - Calculate how much Na is equivalent to the total drug present
3 - Calculate how much Na is needed for an isotonic solution (if no drug was present)
4 - Subtract the Na equivalent calculated in step 2 from total Na needed calculated in step 3.

This problem has a major switch though - because the stock bottle used does not match the script (likely not on hand). So it becomes a logic problem, where you really don't even need the E-value.

0.5% * 30ml = 150mg... which is equal to 1% * 15ml

This covers the drug "needed" to fill the script - but you need 30 mls

So the na content needed is only for 15 mls (for a total of 30ml), as was alluded elsewhere.

0.9% = 900mg / 100ml = 9mg/ml *15ml = 135mg of Na must be added

You wont see this switch on the naplex though - the questions on the naplex are straightforward.