At the one hospital I work, We mix our pit this way: 15 units in 250cc D5W........there is always a bag of LR/NS as a main line which literally does not run when the pit is high, but there nonetheless for safety and if other meds must be given in the same IV (you can flush, you know)....with 250cc, you go up 1 unit, 1 cc. It decreases fluid load this way.
Yes, You can also reconfigure the amt of MGSO4 in the bag, so as to run at a slower rate.......but that must be done w/pharmacy consultation and doctor orders, of course. That it is more concentrated does not bother me if you are running it at the ***proper rate** and do not plan to BOLUS it!
At the other hospital I work we do 20U in 1L LR......it can get tricky, for sure. I like the 15 U in 250cc method better. But then I believe the MGSo4 is mixed differently. I have to check now, I forget! anyhow, there are two suggestions.