Kitty Cold?

So I have 2 cats. One is 11 months and one is 10 months. Booger (11 months) weights about 8 lbs. and Stitch (10 months) weighs about 12 lbs. Last week, Booger's health declined quickly. They both sneeze sometimes, but he started sneezing over and over where I was worried he wasn't breathing enough. Then, before I got him to the vet, he stopped eating and drinking. In less than a 12 hour period, he was fine, then he was so dehydrated by 3pm that the vet had to administer fluids and when I took him home, for 2 days, I had to use a syringe to give him water because he wouldn't move. The vet did blood work and a thorough exam and found absolutely nothing to be wrong with him. It appeared as if it were allergies, but he said sometimes, in cats, you just don't know what the problem is and it goes away on its own. The vet also gave him an antihistamine...chlor something. Long name. So that lasted a few days, and each day he was getting better. Stitch was fine during this. Yesterday was Booger's first "back to normal" days and Stitch started with the sneezing fits. I didn't use all of the antihistamine given to Booger, so I gave one to Stitch and it didn't help at all. I'm thinking dosage issues because Booger is small and Stitch is fat. Late last night he started breathing through his mouth. So I took him in the bathroom and turned on the shower to hot to steam it up for a few minutes. That didn't help. He's still eating and drinking, just doing some sneezing and mouth breathing. Do cats get colds? If so, can they pass it to each other? What we thought was allergies, is clearly not, because Booger is fine and allergies don't just go away after 3 days. I'm confident that whatever it was Booger had, Stitch now has. I just want to make him comfortable for the duration of this. If an antihistamine and steam doesn't help, how do you clear your cats nasal passageway?

Yes, cats can pass cold viruses to each other so it is quite likely that Stitch has the same thing Booger did.  However, he should still go to the vet, especially if the antihistamine didn't work.  It's possible to develop a secondary bacterial infection that requires an antibiotic.  Or he might require a different antihistamine or, as you suspected, a different dose.  You might also ask the vet about giving Stitch some L-Lysine, which boosts the immune system and will help him recover.

In terms of making him comfortable,  you could set up a humidifier near him so he is exposed to a constant level of steam.  Also, keep an eye on his water intake.  You might need to give Stitch water with the syringe if he's not drinking.

Yes cats can definitely share colds. My youngest cat had an upper respiratory infection (URI) and did not show any symptoms for an entire week.  By the time he started sneezing and his eyes got all goopy he had shared his URI with my other 3 cats.  Casey kept on acting like a normal kitten while he was sick including eating/drinking a lot, playing and normal elimination.  I took him to the vet right way when he showed symptoms and he was treated with an antibiotic for the URI and antibiotic ointment for the eye infection.  My oldest cat caught it really bad and also required vet care but never stopped eating or drinking.  My other 2 cats caught a very mild URI and were just sneezing a little so I just used the steam treatment to help them and they were better on their own in a few days.

I would definitely take Stitch to the vet since Booger's cold seems like it was pretty severe.  My cats have never stopped eating due to a cold but I have seen it happen with my friend's cat.   Some cats will not eat if they get to congested and can not smell their food.  I would not wait with Stitch even though he is eating now I would at least call the vet and let him know what is happening with Stitch.

I am not a vet but based on my own experience a cold that is mild tends to respond to steam treatment while the more severe ones require antibiotics to kick in before the steam treatment will help.

I am glad Booger is feeling better and hope things do not get as severe with Stitch.