"A healthcare provider prescribes 500 mg of an antibiotic intravenous piggyback (IVPB) every 12 hours. The vial of antibiotic contains 1 gram and indicates that the addition of 2.5 mL of sterile water will yield 3 mL of reconstituted solution. How many milliliters of the antibiotic should be added to the 50 mL IVPB bag?

1.5 ml

Explanation:

Given that 500 mg of IVPB antibiotic should be administered every 12 hours. 500 mg = 0.5 gm

The antibiotic vial has 1 gm of antibiotic and when mixed with sterile water according to the instruction provided, resultant volume will be 3 ml. Thus, 3 ml of vial has 1 gm of antibiotic.

Required dosage is 500 mg or 0.5 gm so the volume should be halved. 1.5 ml of antibiotic solution should be added to the IVPB bag.  

not too sure but maybe in the hot springs.