calculation for compounding

mehdimons wrote the following at 15:56 on 6/7/10;

Hello everybody , I'm a pharmacy tech student and I didn't understand how to resolve this probleme .

A prescription is written for levothyroxine Na 2.5 mcg/ml, 100 ml to be compounded from crushed triturated with glycerin 40 ml ( levitating agent and rinse for mortar and pestle ) and water ( q.s 100 ml). This compound is stable for eight days when stored at 4 deg C. in amber bottles. How many 0.1 mg levothyroxine tablets are needed to prepare this compound ???

moderator wrote the following reply at 07:59 on 6/25/10;

If you are trying to make levothyroxine 2.5 mcg per mL, then if you are trying to make 100 mL, you will multiply 2.5 mcg by 100 mL or 2.5 mcg/mL x 100 mL = 250 mcg. (read carefully to avoid using the extra numbers they throw in to confuse you such as 40 mL, 8 days, 4 deg C, etc.)

If 1 mg = 1000 mcg, then 0.1 mg = 100 mcg. Therefore, 0.1 mg tablets are 100 mcg each. (memorize your conversion tables)

If you need 250 mcg of levothyroxine and each tablet is 100 mcg, then you'll need 3 tablets since the question asks how many 0.1 mg tablets, not how much levothyroxine. If it asks how much levothyroxine you need, then the answer is 250 mcg. Therefore, the answer is 3 tablets. (carefully read the question)

Therefore, if you read carefully and memorize your conversion tables, you should do fine on other similar pharmacy math problems.

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