Amoxi-drops For Cats Very Sick Cat...hoping For A Vet's Advice...?

Very sick cat...hoping for a vet's advice...? - amoxi-drops for cats

Took my cat to the emergency room last night, not eating, do not respond well and pulled up or driven to a kind of dark green liquid.
ER Vet could not be determined what is wrong with him except that he was) very dehydrated (10%, depending on the test. You want to "wait and see hope," and that a competent professional to give me a second opinion.
The tests that were given with the results:
2.6 points
BUN 70 +
PHOS 4.4
FeLV negative
FIV - negative
280 meters
They gave me amoxicillin to the drops until they are gone, administer 1.5 ml twice daily. Any other tips? It's Sunday, so that he can be a regular vet tomorrow.