I'm sorry your little guy is so sick, Giardia is a nasty little bug that makes you feel horrible, but luckily it is easily treated with the correct medication, which he's on, and hopefully he'll start to feel better soon, if for no other reason than the Giardia count is being pushed out of his intestines by the meds.I hope you have completely disinfected his entire enclosure, inside and out, everything in his enclosure, including his light fixtures, and put down paper towels as his substrate that are replaced at least once daily. The medication doesn't actually kill the Giardia, but rather speeds up the time it takes to be eradicated from his gastrointestinal tract, as people and animals that contract Giardia and get no treatment at all will most likely survive and be rid of the Giardia eventually, but without the medication it takes between 2-3 months for the Giardia to naturally be flushed out of the intestinal tract. People and animals who have been known to have "died from Giardia" did not die from Giardia, they died from usually dehydration, sometimes a combination of dehydration and malnutrition, as Giardia causes the structures on the inside lining of the small intestines that are responsible for the absorption of nutrition to basically shrink or shrivel up, therefore the person or animal doesn't absorb much nutrition from the small amount of food they are able to force themselves to eat...so the medication he's on both speeds up the process of flushing the Giardia out of his body and also should make the side effects of the Giardia a bit less harsh, like the diarrhea, any vomiting or bloating, etc. But the med is also harsh itself.
Luckily Giardia dies very quickly with either antibacterial soaps or just the alcohol-based hand cleaners, I worked with Giardia quite a bit when I worked at the Animal Diagnostics Lab at Penn State, they had labs set up to do research and mass testing, each lab and staff was educated and trained in one specific microbe so they were specialists on that particular bug, they had an entirely separate Avian Influenza testing and research lab, then a few smaller labs that both researched and tested local area farmer's herds/flocks for them...I specialized in Giardiasis and PRRS, a disease caused by a virus that effects the reproductive and respiratory systems in young pigs. Anyway, Giardiasis has a very high recovery rate so no worries there, but I suspect the medication he's on is causing his lack of appetite just as much as the actual Giardia is, it's a very, very effective medication and definitely the right one for a bearded dragon with Giardia, but it's also a pretty nasty drug.
Are you still giving him probiotics? If not, you absolutely need to. Giardia causes extreme stomach pain, cramping, bloating from excess gas, and definitely does not in any way make for a good appetite, lol. If you give him a good probiotic every single day, this should increase his appetite a little more each day. And I'm going to look this up very quickly and confirm it for you after I post this response, but I'm 99% sure that the medication he's on will not be effected negatively by probiotics the way that most antibiotics are, meaning that you can actually give him the probiotic BEFORE you offer him food, and if you do this pre-meal probiotic dose in the form of non-dairy soy yogurt, it will coat his upset stomach and should settle it so that when you offer him food and water he should be a lot more willing to eat some of it, it may even cause him to feel a little hungry. I tend to buy Silk brand non-dairy Soy Yogurt when my guys are on medications and it works very well. Any Walmart and most grocery stores sell the Silk brand Soy Yogurt in the regular yogurt section, and my guys seem to like the fruit flavors, like Strawberry, Raspberry, Blueberry, etc. You can offer him the non-dairy Soy Yogurt first thing in the morning but after his lights have been on for at least an hour or two. I typically just open up the container of Soy Yogurt, mix it up really well to kind of thin it up a bit, and then it should be thin enough to be sucked-up in an oral syringe or eyedropper (I tend to use an eyedropper for this because I'm not putting it inside their mouths, just dripping it on their nose so it runs over their lips). Typically they really do like the fruity Soy Yogurt, hopefully he'll like it, and you should give him as much as he'll eat (realistically he's not going to eat a bunch of it, but even a small amount will coat his stomach, help to neutralize the stomach acid, will boost his blood sugar, which is bound to be low, and hopefully make him hungry for his regular food). Then wait like 10 to 15 minutes after he eats the Soy Yogurt to see how he reacts to it, hopefully that will perk him up a bit, and then offer him his live bugs, greens, veggies, etc. ABSOLUTELY BE SURE THAT ANY SOY YOGURT YOU GIVE HIM IS NON-DAIRY, AS LACTOSE INTAKE IS A VERY, VERY, VERY BAD THING WHEN YOU HAVE GIARDIA...it's not pretty at all...
Because Giardia typically does cause dehydration in most cases, and it is particularly dehydrating to bearded dragons because they get most all of their
hydration from their live bugs and greens and don't actually drink water out of a bowl or
bath, I would also pick up 2 more items to try to keep him
hydrated with in addition to the non-dairy Soy Yogurt: #1) Some Pedialyte or the generic, store-brand version of Pedialyte, and #2) Some beardie-safe fruit.
Pedialyte is sugar-free, and will provide both fluids and much-needed electrolytes to your beardie while he's suffering from both the Giardia and the side-effects of the medication. Even if you only get him to drink/lick off a very small amount of the Pedialyte, a very small amount of Pedialyte is a lot more
hydrating than a very small amount of water, so this is a no-brainer. You can offer it to him the same way you have been offering the water or fruit juice, by using an eyedropper to drip it down over his lips and seeing if he'll lick it off, or you can try get just a little bit in his mouth by using an oral syringe (NEVER DO THIS WITH A GLASS EYEDROPPER BECAUSE THEY CAN CHOMP DOWN ON IT). This method is actually quite easy and not stressful to him at all, unlike some of the other force-feeding methods, like using a piece of cardboard, etc. All I do is put a very small amount of the Pedialyte or slurry or whatever it is that I'm giving them in a plastic syringe (either an oral syringe, or better yet I go to Tractor Supply and buy a box of 6 disposable, plastic syringes, the LEUR-SLIP type with the longer tip, not the leur-lock type, and usually get either the 1ml or the 3ml ones, 3ml is better). A box of 6 disposable, plastic, 3ml Leur-Slip syringes (no needles obviously) at Tractor Supply costs like $1, lol. Suck-up only a small amount of the Pedialyte into the 3ml syringe, like 0.5ml of pedialyte, because you can safely push this tiny amount into his mouth without causing stress or without him choking on it. All you do is put 0.5ml of the Pedialyte in the plastic syringe, then using the tip on the end of the syringe, push up his upper lip on the side of his mouth, back near his ear, at the very end of his mouth. Have your thumb on the plunger and be ready to slowly push the Pedialyte into his mouth...once you have the tip of the syringe under his upper lip on the side of his mouth/face, gently just slide the tip of the syringe up his mouth, keeping it under his upper lip the entire time, towards the front of his mouth in the middle of his face. For whatever reason, when the tip of the syringe reaches the middle of his mouth under the tip of his snout, he will pretty much automatically open his mouth up wide. They all do it, I don't know why but in my experience they all do. Since the tip of the syringe was already under his upper lip and stayed there the entire time as you slid the tip up to the middle of his mouth, all you have to do when he opens his mouth is slowly but steadily and firmly push the plunger, the tip of the syringe will already be inside his mouth when he opens it. You're pushing such a small amount of Pedialyte that he'll hardly notice that he's
drinking anything, but you'll see him lick a bit, then close his mouth again. Once you do this a few times it's very, very easy and will go so smoothly from this point on, so if you every need to force fluids or even slurries or Critical Care again in the future, it will be simple, quick, and stress-free for both of you. Force-feeding can be so stressful on both the beardie and the person doing it that it backfires, which is why I don't use the other methods, like prying their mouths open with the tip of the syringe, or inserting a piece of flat cardboard between their lips and teeth until they open up, these methods may work for some, but once you do this a couple of times you'll realize what I mean when I say it's simple, quick, and not at all stressful. You'll need to do this a few times since you're only giving him 0.5ml of Pedialyte or whatever at a time, but this is both the safe way to do it, and the easy way, as you're giving them so little that they hardly know they're eating or
drinking anything. I'd try to get 2-3ml of the Pedialyte in him at a time, and I'd do this twice a day until he starts eating normally again. The extra electrolytes provided to him by giving him 4-6ml of Pedialyte a day will help him recover much more quickly and make the illness and the medications much easier on his kidneys. If you can comfortably get him to take more of the Pedialyte throughout the day then by all means do so, but I always try to give no more than 2-3ml in one sitting, again 0.5ml at a time, because this is so much less stressful than trying to give him larger amounts at one time. So if you give him 2-3ml of Pedialyte in the morning after his lights have been on for at least an hour or so (you can also give him the Soy Yogurt this way, and actually at the same time by thinning the Soy Yogurt with the Pedialyte, so you only have to do this to him once), then give him another 2-3ml around lunch, another 2-3ml at dinner, and a last 2-3ml before bedtime (try to leave his lights on for an hour after giving him the last serving of Pedialyte, water, food, etc. so he digests it), he'll get a good amount of fluids, electrolytes, and the Soy Yogurt containing the probiotics, and he'll get them all in very small amounts over time which is not only quicker but also much less stressful. You can try a fruit-flavored Pedialyte, sometimes they actually really like it, just like they like regular fruit juice, or you can just use the unflavored Pedialyte, doesn't matter.
The second thing I suggest is buying some fresh fruit and offering it to him along with his fresh greens. I know that younger beardies don't typically eat a lot, if any greens and veggies. Some love them and they have lucky owners, but most won't touch them, which is a bummer when they're sick because of all the
hydration they would get from greens and veggies. However, they usually all like at least one or two types of fruit, and fruit contains more
hydration than greens, veggies, and even the live bugs. The only issue with feeding them a lot of fruit is that it also contains a lot of natural sugar (fructose). That being said, since your poor little guy isn't eating a whole lot of anything and is also in danger of becoming very dehydrated, there is no danger in giving him a little fruit each day until he starts eating regularly. He will feel quite a bit better after eating some fruit each day, not only because it's very
hydrating, but also because he could use the extra sugar. You can give him many different types of fruits, but never ever give him ANY Citrus fruits. Other than not giving him any citrus fruits, they pretty much seem to love fresh Strawberries, Raspberries, Blueberries, Apple Slices/Cubes, Blackberries, Grapes (SEEDLESS), Cherries (SEEDLESS/PITLESS), Mango, and any types of Melon like Cantaloupe, Honeydew, etc., and my little 5 month old Dee Dee goes absolutely insane for Banana!!!! He loves bananas more than any live insect, any day of the week. I have no idea why, my 2 other guys won't touch banana, but Dee Dee would eat an entire, full-size banana if I let him, lol. Every beardie is different in their tastes, just like people are, so I always buy little variety fruit cups at the grocery store that have cubes of all different types of fresh fruit and usually some grapes, and I cut them up into tiny little pieces and let them all try them all, and look to see who ate the most of what. Of course they all like something different, lol. But actually I forgot to mention that, that cutting up both greens/veggies and fruits up into different sized pieces can also help them eat more, because some of them like them cut up into tiny little pieces, and others like them a little bigger. So you can try it all different ways and see what trips his trigger.
By the way, I just googled the medication he's on, and probiotics will not interfere with it at all, so you do not have to wait a certain time period before giving it to him. So if he's taking the medication orally (I don't remember if you said orally or by injections) I would make sure his lights are on for at least an hour in the morning, then give him the non-dairy Soy Yogurt to coat his stomach, wait like 10-15 minutes for the yogurt/probiotics to settle, and then give him his dose of medication. That will make it so much easier on his poor little tummy...
I've rambled enough now, sorry, I just know a lot about Giardia and how to combat it, and I have been following your story since you first posted it and he's been struggling so, I want to help in any way I possibly can. Plus I know how Giardia tends to cause very horrible dehydration and malnutrition/weight loss in both people and animals/reptiles, and how important
hydration and nutrition are to getting over Giardia, because technically the medications available do not "cure" or kill the Giardia, they just speed up the process of flushing it out of the body.