Pharmacy Math Question

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Comments (2)

Lorian43 in Apex, North Carolina

46 months ago

Heather,

What you want to do first is calculate what your original strength is per ml.
You have phenobarbital 20mg/5ml - if you divide 20mg by 5ml, that equals 4mg/ml

The formula for this problem is final volume over initial volume = initial strength over final strength.

Final volume is what you are solving for or (x)ml = 4mg is initial strength
Your initial volume is what you have on hand 100ml & 2mg is the final strength

Or (x)ml over 100ml = 4mg over 2mg; Then you cross multiply.

So that you would have 2mg times (x) = 100mg times 4mg or 2(x) = 400. Since you are solving for (x) you would divide 400 by 2 and you get 200ml. You already have 100ml so you would just need to add another 100ml of cherry syrup to your original 100ml to equal a concentration of 2mg/ml.

Hope that helps

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amy mal in Long Beach, California

25 months ago

The recommended dose of phenytoin sodium is 6 mg / kg / d administered in three equally divided doses. The phenytoin stock suspension is available in a 12 5 mg / 5 mL concentration. How much should be given to 44 lb. child for each dose?

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