Question

A hospital pharmacist prepared thirty 100-mL epidural bags containing 0.125% of bupivacaine hydrochloride and 1 μg/mL of fentanyl citrate in 0.9% sodium chloride injection. How many (a) 30-mL vials of 0.5% bupivacaine hydrochloride, (b) 20-mL vials of 50 μg/mL of fen-tanyl citrate, and (c) 1-L bags of 0.9% sodium chloride were required?

Answer 1

Ans. Total volume of solution prepared by the pharmacist = 30 bags x 100 mL

            = 3000 mL = 3.0 L

A. Concentration of bupivacaine in final solution = 0.125 %

            Total amount = 0.125 % of 3000 mL = (0.125/ 100) / 3000 = 3.75 gram

Concentration of bupivacaine in original (undiluted) solution = 0.5 %

            Amount in 30 mL vial = 0.5 % of 30 mL = 0.15 g

Now,

            0.15 g is present in 1 vial

            Or, 1 g -           -    (1/ 0.15) vial

            Or. 3.75 f           -     (1/ 0.15) x 3.75 = 25 vials    

B. Total amount of fentanyl citrate in final solution = final concentration x final volume                

                        = (1 ug/ mL) x 3000 mL = 3000 ug

Amount of fentanyl citrate in 1 vial (20 mL) original solution = concentration x volume

                        = (50 ug/mL) x 20 mL = 1000 ug

Now, number of vials required = total amount in final solution / amount in 1 vial

                                                = 3000 ug/ 1000 ug = 3 vials

c. Total amount of NaCl in final solution = final concentration x final volume                    

                        = 0.9 % (w/v) x 3000 mL = 27 g

Amount of NaCl in 1 bag (1000 mL = 1L) original solution = concentration x volume

                        = 0.9 % (w/v) x 1000 = 9.0 g

Now, number of bags required = total amount in final solution / amount in 1 vial

                                                = 27 g/ 3 g = 3 bags