I only read the first post here so sorry if this is echoed advice. I have a bun who deals with chronic slow gut motility and full blown Stasis at least once a month or 2.
Make sure your pellets are by Oxbow. They have the highest fiber content.
The antibiotics were likely prescribed to kill off any build up of bad bacteria in the gut which can happen when stagnant contents just lay in there (hence the stink that comes out when the gut gets moving again). The Baytril is fine but you should never give a bunny any type of cillin or cephalosporin antibiotic because it can throw off their gut flora. I have heard it can be safe when injected so it bypasses the gut flora, but double check with a rabbit wise vet. I would take him off the Penicillin ASAP.
Cecal dysbiosis, that nasty, goupy, yellow mucus that starts to come out after a bout of bloat/stasis - is the build up of bad bacteria and the key to getting bunny through it is hydration and Bene-Bac, works better than throwing them on antibiotics which is quite stressful to them. Go to any local pet store, buy the 4 little tubes (make sure they are not expired). Give 1 tube twice, 3 days apart. I've also noticed that when my bun is *starting* to get constipated or lose his appetite, Bene-Bac sometimes prevents a full-blown attack. Bene-bac is probiotics, "good" bacteria for the gut.
The key to getting a bun through stasis is keeping him hydrated and not in pain - and when you have to force-feed, do it with small amounts at a time because too much can just make them more in pain. simethicone (in infant drops, 0.3ml) can help break up gas buildup and the metacam is also a good idea.
The motility meds should only be used for a week, maybe 2 weeks at most, but in my experience, any longer than that and your bun can become dependent on it and the bun can have rebound stasis when you stop giving it to him after such longterm use and he gets dependent on it. To help combat this I use motility meds as a last resort, with extreme caution, and I switch between Cisapride and Metoclopromide interchangably when I do have to use them.
when I HAVE to resort to motility meds, I try to figure out if he is stopped up in the upper GI tract or the lower GI tract. If upper, Reglan (metoclopromide) helps, but I am careful to only use it for a few days to a week or 2, and if he is constipated in the colon with poops, I would reach for the Cisapride and again, no more than a week or 2.
But I usually try other ways first - removal of pellets for the first day, enticing with more varieties of hays (oat is very tasty to buns and great in stasis) and WET leafy greens, sub-Q fluids (or syringe feeding him pedialyte) (I have had to learn to administer subQ fluids myself due to the frequency of my bun going through this), simethicone, metacam, Critical Care, and gentle but aggressive belly rubs. Make sure bun is also allowed to get a lot of exercise - it can promote motility in his gut and make him work up an appetite.
When this slowdown happens (and sometimes before resorting to risky motility meds) I have given 1-2mL of medical grade Mineral Oil laxative by mouth, only once per bout of stasis. you don't want to give him diarrhea. You can get it at any pharmacy. If your bun is bigger than 3lbs, 2mL would probably be more appropriate. It takes a day to work, but it usually does.
Finally, when I am desperate, I administer about 3mL of medical grade Mineral Oil laxative as an enema into my bun's colon with a small syringe - administered through his anus. You can also use an infant's ear dropper bulb and mix 3mL of the mineral oil with about 5mL room temperature (lukewarm) water and shake up into the infant bulb syringe (or ear bulb syringe). to administer, all you do is get bun on his back, find the anus (it's the hole that winks back at you), insert, and gently and slowly administer..... then keep bun on his back for a few minutes, grab him by the hind quarters and lift them up a bit so as to get all of the enema to travel as far up the lower GI tract as possible, keep it there for a few more minutes, rub his belly and then set him down in his litterbox. If successfull....He should produce poops by then. The lukewarm water itself will help stimulate the GI tract and hydrate the dried up compaction inside and the mineral oil, as a laxative will ease the fecal matter out.
That said, the following I am going to write to you for FUTURe reference..............It sounds like your bun is very young and for him to be experiencing stasis issues already is kind of a bad sign - my bun is not even a year old yet and has been in stasis at least 5 times. The key to keeping it under control is lots of hay (oat hay is GREAT for stasis buns because rabbits love the taste and it is nutritionally similar to timothy, so mix that with the timothy!), keep them on Oxbow pellets and only give those in tiny amounts through-out the day so they don't load up on the pellets and make themselves constipated. With these kinds of buns, daily greens is also a must....and usually herbs like cilantro and basil combined with endive, carrot TOPS (not the orange carrot part) and escarole are the least risky (some greens can have side effects if given regularly...these greens I've found to be very safe to use on a longterm basis). My bun also has to have at least a few hours of exercise, so you might need to figure out a place where he can run, binky, jump and hop around for a few hours a day.
Because my bun nearly became dependent on the motility meds (which is BAD because it will stop working after a while and you are then unable to take them off due to dependency) I give him 1 small tube of Bene-Bac every other day. (the small tubes that come in the packages of 4). So, diet, benebac and exercise so far has been my routine, and when he shows signs of slowdown, I start with 2 tubes of the Benebac, a belly rub, simethicone and fluids/remove pellets/add more hay and veggies, let him run around and get moving..... if no better despite that, I administer the 1-2mL oral Mineral Oil laxative and metacam with small amounts of Critical Care through out the day, keeping him warm and hydrated (again, I do subQ fluids) if he still then gets worse just keep him hydrated and keep rubbing his belly and when all else fails...... the motility meds. WHen THOSE fail (in my bun's case it was because he was on them too long- I feel that 2 weeks is the max for those drugs) that's when it's enema time. It'd also be a good idea to ask the vet to have motility meds available for recurring bouts of bloat, I have done this. So if it's a weekend and all else is failing, they are there in my cupboard for him. But again, after he started to get dependent on them I use them with extreme caution these days.
I hope your bun gets better soon----and remember, once he gets the yuck out it's BeneBac time! Feel free to PM me if you need any help, and contact any local rabbit rescues for their advice as they often deal with their buns going into stasis on the weekends when vets are often unavailable.