giardia and my cats

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

Regarding the medication name: Telephone your vet. Ask what it is. The staff at the desk can look it up in your chart. Then write it on the bottle. Giardia is a parasite, so the drug is designed to kill it.
   
IMPORTANT: There is no cheap way to diagnose a pet. If Lizzy starts showing symptoms, you will HAVE to get the test done on her; I looked it up & the test isn't easy to do. You can't take the chance that she MAY have Giardia, you have to KNOW before you drug ANY cat.
   
Do NOT give Lizzy any of the kitten's medication. The medication was measured out for a kitten, that kitten. There will be very little extra medication, & you won't know the dosage for an adult cat. The kitten MUST have the entire course of treatment so that the Giardia bug will be sure to be eliminated.
   
In fact, I'd have Lizzy tested anyway, as not all cats with Giardia actually show symptoms.
   
How expensive is "expensive"? $50, $100? $50-$80 is a normal price for a test. Remember, you don't have health insurance on your pet, so you pay the entire cost. Humans with health insurance have no idea what medical procedures actually cost; vet care shows you what real costs can be.
   
By the way, you can get pet health insurance, you can look into it on the web.