Question

A diphenhydramine elixir contains 12.5 mg drug in one teaspoon. The volume of

oral vehicle that is to be added to 100 ml of this elixir to reduce its strength by one

half its original strength is:

Answer 1

SOLUTION:

1 teaspoon of elixir contains 12.5mg drug

or 4.93 mL of elixir contain 12.5mg drug

Because 1 teaspoon = 4.93 mL

This can be equated as

4.93mL elixir = 12.5 mg Drug

1 mL of elixir = 12.5 / 4.93 = 2.53 mg

It mens 1 mL of elixir contains 2.53 mg of drug

Therefore 100 mL of elixir will contain = 2.53 X 100 = 253 mg of drug.

So the strength of elixir = 253mg/100mL

To reuce the strength to half i.e. 126.5mg/100mL we have to add 100mL oral vhucle ,

so the total volume = 100mL elixir + 100mL oral vehicl = 200ml

Strenghth (in mg/100mL0 = (mass of drug / total volume ) X 100 = ( 253 / 200) X 100 = 126.5 mg/100mL