Should be holding of on all meds unless it is known to be required.
Calves often have runny poop. I would say it is normal & especially when new to replacer for a few days at least, after a few days loose is still ok, but it should not be like a watery stream or burst or have blood, watch hydration closely if very loose and watery.
What you need to look for is behavior & changes and or departure from normal, changes can be subtle.
If the calf is energetic, taking its feed with vigour and showing no signs of dehydration, then just keep feeding them and watching. Follow the directions on powder amount and mixing on a quality milk replacer, do not be tempted to vary or feed a lot more.
As per cowgal, offer a starter pellet and mix in some chaff so they can nibble, also, a water source, they will still drink water too.
Make sure they get the milk, they need it. It is no 1.