Are they showing signs of hypocalcaemia? If yes, I would inject under the skin over the ribcage, and 50 to 80 ml is the recommended dose ((Calciject 20CMD) in at east two different locations. Also warm the solution up. It does sting and they don't like it!
If severe (as in they are down) I would call out the vet to do it by IV - they respond much quicker.