In the name of Allah the Inspirer of truth
Gelatin has been considered haram according to the majority of scholars unless it is from a vegetarian [f: or halal-slaughtered] source. This unfortunately cannot be determined here. What needs to be done here is that a suitable alternative has to be found. Calcium and vitamin C is probably not a difficult combination to find in caplet form rather than in a capsule.
The doctor can also be consulted along with the pharmacy to find a suitable alternative. The doctor may be able to change the prescription or the pharmacy can substitute the original ones for the non-gelatin type.