The formula for an ophthalmic ointment is as follows: Sulfacetamide Sodium 10% w

Question

The formula for an ophthalmic ointment is as follows:

Sulfacetamide Sodium   10% w/w

Prednisolone Acetate   0.2%

w/w Phenylmercuric Acetate   0.0008%

w/w Mineral Oil   1%

w/w White Petrolatum, qs ad   3.5 g

How much of each ingredient would be needed to manufacture 2000 such tubes of ointment?

The answers from the book are

700 g sulfacetamide sodium

14 g prednisolone acetate

56 mg phenyl mercuric acetate

70 g mineral oil

Will you please, show me the steps for the calculation? Thank you!

6215.944 g white petrolatum

Explanation / Answer

For 2000 such tubes of ointment, we need total 7000 grams of all ingredients (if we consider white petrolatum 2000 X 3.5 = 7000 grams but we need to substract it from the total of rest of the ingredients).

Sulfacetamide Sodium 10% = 7000 X 10/100 = 700 g sulfacetamide sodium

Prednisolone Acetate 0.2% = 7000 X 0.2/100 = 14 g prednisolone acetate

Phenylmercuric Acetate 0.0008% = 7000 X 0.0008/100 = 56 mg phenyl mercuric acetate

Mineral Oil 1% = 7000 X 1/100 = 70 g mineral oil

White Petrolatum, qs ad   3.5 g = 2000 X 3.5 = 7000 grams. So, 7000 - (700 + 14 + 0.056 + 70) = 6215.944 grams. Therefore, 6215.944 g white petrolatum.

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