Cerenia & Metronidazole Causing Counteracting Anti-Nausea Effect?

Hey everyone, 
I'm brand new here so please excuse any post naivety. I've googled many things about my cats over the last 2 years and your forum has consistently popped up with awesome insight so I finally thought I'd join. 

My question is for my little guy Buddy, neutered, Maine Coon cross. He was a foster fail so I don't know a lot about his health history prior to him becoming my fur babe but he is estimated to be about 4 years old and I've had him since he was 2. As of Saturday night, Buddy threw up a little hairball along with some bile. I didn't panic as both him and his brother are still shedding their winter coats as we've had irregular heat this spring/summer and despite my brushing, they both will have the occasional hairball. However, at about 5 am Sunday he threw up more bile. And then again about an hour or so later. Same thing and almost same exact timing today, plus more (twice consecutively) after giving him 6ml of water with a syringe.

So I went in to see the vet who ran a Snap test that came out negative for pancreatitis. Since I found Buddy in this same situation a little over a year ago, the vet is thinking he may just have a sensitive GI or a blockage.

Anyway, we decided on symptomatic treatment for the time being and my main concern is that despite being given a Cerenia shot almost 5 hours ago, he is still refusing to eat and he's actually showing less interest in his food than he was yesterday. At least yesterday he was super interested, seemed hungry, but as soon as he smelled the dish he would smack his lips and walk away. I've read some posts here saying that one of the symptoms is a suppressed appetite which I find surprising since I thought it's supposed to act as an anti-nauseant as well.  

He is also on an antibiotic called Metronidazole which I'm not familiar with so I'm wondering if the combination is what's causing him to still lack an appetite? Thoughts? How long can he go without eating? The last I saw him eat was Saturday night so I'm getting super worried...

Thanks in advance! 

Sniffing food, lip smacking and walking away are signs of nausea.  Cerenia works by inhibiting neurokinin (NK) inhibitors. In other words, it works by blocking the stimulation of the part of the brain that instigates vomiting.  So it is not truly an anti-nausea medication, it is an anti-emetic.    Your  kitty may do better with Ondansetron(Zofran), which is a human drug used to combat nausea in chemotherapy patients.  It has been used very effectively in kitties, my Tiger did very well with a combination of Cerenia for her vomiting and Ondansetron for nausea. 

Metronidazole is an antibiotic, typically  it is given for diarrhea.   I don't see that you mentioned your kitty having diarrhea so I am not sure why it is being given. It can be constipating as well. When did your kitty last poop?  Constipation can cause vomiting.  Metronidazole,  I can tell you, it is horrible tasting, especially if given in a liquid form, your cat will hate the taste. And most antibiotics are hard on the stomach, you might want to ask your vet why it is being given and if it could be countered with a good probiotic.

We need to get your kitty eating--can you try offering baby food, I keep jjars of BeechNut Turkey and Chicken around.  But he needs to eat whatever  he will eat! If he is not going to eat you might need to get him back to the vet. Sending healing and feel better vines.

Thanks Ruth! Both take-home meds I was given are pill form. He only gave him one Cerenia shot during the visit.

And, yes Buddy's stool was a little soft yesterday, then this morning there was diarrhea but if it is going to irritate his stomach more, I don't understand why it would be given either. He did mention being worried about a worm earlier in the appointment (I was there for over an hour and a half waiting for the blood work) but he didn't revisit it when discussing medication. Maybe I'll give him a call tomorrow morning. I don't have any baby food on hand but I'm going to go out quickly to get some, really hoping he eats something before bed 

You could also try poaching chicken breast meat(no onion or garlic) or even deli roasted chicken might work?  When my kitten Buster quit eating, the vet  gave him AD and he loved it.

I tried 3 different baby foods, he liked zero but his brother liked all 3 haha. Go figure. I syringe fed him 6ml of the Chicken and Broth flavour just to see if he could keep it down and he did. So I went to the emergency vet and bought 2 cans of the AD, managed to syringe feed him about 1 and a quarter ounce of it mixed with some water. Not great but it's something. He was smacking his lips a lot so I called it quits - figured it's pointless to feed him more than he can handle since he might throw it up. So far so good though, fingers crossed it's enough to bring back his appetite in the morning! (And wards off that awful fatty liver disease!)

Thanks again Ruth