"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.  

thinking it would be d not too sure but i think it's right