Question

how many milliliters of a 4% lidocaine hydrochloride topical solution contains 300mg of lidocaine hydrchloride?

Answer 1

The concentration of lidocaine is expressed in mass by volume percentage.That is the amount of lidocaine in a unit volume of the solvent(100mL).This is given by

Mass by volume percentage = Mass of the solution in g / Volume of the solution in mL x 100

4 = x / 100 x 100

x = 4 g

Which means 4 g(4000 mg) of lidocaine is dissolved in 100 mL of the solvent..

i.e; 4000 mg in 100 mL solvent.

Therefore, 1 mL for 1 ml solvent amount of lidocaine = 4000/100 = 40 mg lidocaine

Now,

In order to find out the amount of the solution which contains 300mg of lidocaine, the following calculation may be used:

We have ,

40 mg = 1 mL

300mg = x

40 x = 300

x = 300 / 40

= 7.5 mL

Therefore, 7.5 mL solution contains 300 mg of lidocaine hydrochloride.