Question

Rx Tetracaine HCl 0.5% Epinephrine bitartrate 1:1000 Boric Acid qs Purified Water ad 45 mL M. Ft. Isotonic Solution E-values: Tetracaine HCL (E=0.18); Epinephrine Bitartrate (E = 0.18); Boric Acid (E = 0.52) How many milligrams of boric acid are need to prepare this prescription? The amount of boric acid = ______ mg.

Answer 1

Rx Tetracaine Hydrochloride 0.5%

Sol.Epinephrine bitartrate( 1:1000 ) 10

Purified Water ad 45 mL

E value of tetracaine Hydrochloride (E = 0.18)
tetracaine Hydrochloride calculated as shown below

0.5×45/100 =0.225

0.225 x 0.18 = 0.0405 g of sodium chloride represented by tetracaine Hydrochloride

0.18 g - 0.0405 = 0.1395g of sodium chloride

required to make the solution isotonic
But because the prescription calls for boric acid:
0.1395 g ÷ 0.52 (sodium chloride equivalent of boric acid) = 0.268 g of boric acid to be used