Struggling with Pharmacy Calculations

[pharm313]

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Hey guys,

I've been struggling with pharmacy calculations this past semester and wanted to know if any of you knew of good resources to help learn the material and/or provide good practice problems.

Some of the material in particular I have been struggling with:
- mEq
- milliosmoles
- half-lives
- conversions between pints, fluidrams, ounces, ect
- how to compound a cream with a certain % of the drug when you have 2 different %'s of the drug

 

[mustang sally]

We learned all of our pharmacy math from the Stoklosa book, Pharmaceutical Calculations. I thought it was a pretty good reference and it covers everything you mentioned above with the possible exception of half lives (that fell more under kinetics in our curriculum). I would ask your professor, a classmate, or a teaching assistant to explain any problems you don't understand.

There's also the SDN 120 calculations packet floating around somewhere on here for extra practice problems. You can probably find it in the licensing and exams forum.

 

[cjb56]

We also used the Ansel/Stoklosa book, but for a more basic and clear pharm calc book, try Pharmaceutical Calculations by Joel Zatz. You'll find much better explanations in Zatz, with easier examples. After you master the Zatz material, move on to the more advanced Ansel/Stolosa book and you will find those practice questions easy to do.

 

[Old Timer]

There are books? You need more than one page? 99.999999999999999999999% of all pharmacy calculations are algebra 1.

Most problems are word problem variations on the algebra one ratio and proportion problem.

Conventions

1. Any number divided by itself is one.

2. Any number multiplied by 1 is that number.

3. A fraction is a division problem where the denominator (bottom number) is divided into the numerator (top number).

4. Anything you do to one side of the equation you must do to the other side.

All problems are a variation on the following word problem:

A train is going 60 miles per hour. How long will it take to travel 300 miles?


60 miles 300 miles
---------- = ------------ Ratio & Proportion
1 hour X hours

Now you cross multiply to solve for X. So the equation becomes:

60 X = 300

Now using the principles we learned above, divide both sides of the equation by 60:

60X 300
------ = -----
60 60

So we divide both sides by 60 getting

X=5 hours

If the problem has two parts, always start buy figuring out what you need. Once you have determined what you need, you can determine how to get it from what you
Accepted information:

1 teaspoonful....................5 ml or 5 cc

1 kg...................................2.2 lbs

1 gr....................................60 mg

1 oz....................................30 ml

%.........................................gm/100 ml

%.........................................gm/100 gm

1 tablespoonful....................15 ml

U-100 insulin.......................100 units/ml

Let's take your cream problem. You need to make 30GM of Hydrocortisone cream 1% and all you have is the 2.5%.

Step one: What do you need? 1gm/100gm=x gm/30gm then cross multiply and solve for x.

100x=30 so x=0.3gm

Step Two: What do you have? 2.5gm/100gm=0.3gm/x gm. Cross multiply and solve for X. 2.5X=30 x=12gm

Result: So you would need 12 gm of hydrocortisone cream 2.5% and 18gm of base to make 30gm of Hydrocortisone cream 1%

You are always given 3 parts of the problem, You need to solve for the 4th part.

 

[pharm313]

Very helpful info, thank you all so much! 🙂

 

[Sparda29]

This is the one part of pharmacy school that I loved.

 

[WVUPharm2007]

There are books? You need more than one page? 99.999999999999999999999% of all pharmacy calculations are algebra 1.

Back last year when bicarb solution went off the market and we had the "club soda" incident(s), I had to bust out some Calculus and figure out the appx rate of drug deterioration given the pH of the substituted solution to figure out how long the drug was actually good for (to my shock, it was probably still good for a weekend or so)...and then I had to figure out a new way to do it without the syringes...all by myself...at like 4AM...in a retail pharmacy.

See...you can be a science nerd in any pharmacy setting.

 

[Sparda29]

Back last year when bicarb solution went off the market and we had the "club soda" incident(s), I had to bust out some Calculus and figure out the appx rate of drug deterioration given the pH of the substituted solution to figure out how long the drug was actually good for (to my shock, it was probably still good for a weekend or so)...and then I had to figure out a new way to do it without the syringes...all by myself...at like 4AM...in a retail pharmacy.

See...you can be a science nerd in any pharmacy setting.

Couldn't they just use sodium acetate instead?

 

[WVUPharm2007]

Couldn't they just use sodium acetate instead?

Well, it's pKa is lower, which would lead to lower stability when used for omeprazole/lansoprazole solutions as in a retail setting...not to mention the fact that it would probably taste like salty vinegar.

 

[Sparda29]

Well, it's pKa is lower, which would lead to lower stability when used for omeprazole/lansoprazole solutions as in a retail setting...not to mention the fact that it would probably taste like salty vinegar.

Ah for the retail setting and compounding that stuff. I thought you meant for IV solutions.

 

[rxlea]

Bicarb shortage was a pain in the ass. Nothing like making bicarb IV from the powder we already had

 

[WVUPharm2007]

Bicarb shortage was a pain in the ass. Nothing like making bicarb IV from the powder we already had

I don't even want to imagine what it did to critical care units. Those things are in every crash cart in the country.

 

[rxlea]

I don't even want to imagine what it did to critical care units. Those things are in every crash cart in the country.

It was ****ing horrible