First what you need to do is start a sketch, what i did is i made a square on the top plane and filleted the edges, and just eyeballed it so it would look like it does in the game.
Then i made another plane and made lower than the original one and made a smaller square and filleted the edges again.
After that i made a plane slightly lower than that and made a circle.
Then i lofted all three of those together and i got the shape that i have in the picture.
Once you have done all of that you will have the basic shape of the plasmid.
** I'm sorry for the weird resolution pictures i don't know how to screencap just one of my monitors. **
Step 1: Adding the Extra Details.
Know you want to chamfer the top edge of that circle I set the diameter of mine to 0.075 Inches, and the angle to 55 degrees.
The plasmid is starting to take shape know.
Once you have all the previous things finished you will want to draw another circle on top of the circle you just extruded and extrude that higher than the previous one.
(Again you can just eyeball, just image search bioshock plasmids on google, and you can get a good idea of the height of things).
Once you have that extruded you will want to chamfer that as well. I chamfered mine 0.04 inches on the diameter and 60 degrees for the angle.
Step 2: Adding the Curls on the Side.
Once you have that you want to extrude the sketch so it looks like it does in my first picture.
We want to circular sketch pattern the extrude that we just did so there are 4 total curls and it looks like it does in my picutre
Now just fillet the curls to your liking (or don't at all) and then you will be good!