Kitten and Giardia

My kitten was diagnosed with Giardia yesterday. I am not sure of the medication prescribed because the name of it is not written on the bottle. The medicine is liquid and is white and chalky. We are supposed to give this to him 2x a day for 7 or 8 days. Now my other cat who is a year and a half is def at risk of contracting this. She has shown no symptoms but sometimes the kitten will poop in her litter box. Now if my older cat Lizzy starts showing signs like persistent diarrhea is it safe to give her the same medication I am giving my kitten. It was very expensive to get a lab test for the kittens stool and was wondering if there is a cheaper way of treating my older cat

Answer by Kate
The answer is simply "absolutely not". Without a proper diagnosis it could be dangerous to treat with medication which is not prescibed.
You cannot know for sure what is wrong with your cat unless examined by a vet and guessing can be so dangerous.
I absolutely understand how hard it can be to afford the cost of vets bills, but it is one of the responsibilities we take on when we own a cat and that is why i have pet insurance because I have been stung before.
Please don't misunderstand me I am not preaching I am just telling the truth. If your cat is Ill they need to see a vet for themselves, sorry.

best wishes Kate