Reconstitution Question!!

Hi everybody,

I am half way done with my nursing calculations course, and thus far I have understood everything pretty well, but we have just moved on to reconstituting powdered medications and I am completely confused. For example:

Order: Give gr xv Geopen IM STAT

Information on label:

Geopen - equivalent to 2g

IM Use: Reconstitute with at least 4ml of sterile water. In order to faciliate reconstitution, up to 7.2 ml of sterile water can be used.

Amount of diluent to be added to the 2g vial:

• 4.0ml
  
• 5.0ml
  
• 7.2ml
  

Volume to be withdrawn for a 1g dose:

• 2.5ml
  
• 3.0ml
  
• 4.0ml
  

What I can't understand is how do you know how much diluent to use when it is variable and doesn't just say one amount.

If this doesn't make any sense, another question is:

Order: Prepare Penicillin G Potassium to give 300,000 U IM q6h to an adult.

Information on label:

Penicillin G Potassium - 1,000,000 U

Add Diluent Concentration of Solution

-9.6ml 100,000 Units/ml

-4.6ml 200,000 Units/ml

-1.6ml 500,000 Units/ml

Any insight on any of this would be very helpful.

Thanks!