How you take the ketamine does not matter for bladder damage; it's the metabolite nor-ketamine that causes the damage to the bladder and no matter how you take it; your liver wíll metabolize it and once your (daily..) dose gets too high your bladder will suffer and it is not pretty. Mild symptoms are shrinkage of the bladder so you will pee more often; once that starts there's really only one thing that prevents further issues: cut down.
I must add, issues typically only occur when using serveral grams a day and usually only with daily use, although when you have a proper tolerance abusing too much ketamine for like 3-4 days can also cause bladder issues. Cutting down to less then a gram a day or taking a one or two week break will have the symptoms heal up again, atleast if they aren't too bad yet. A friend of mine no longer has any benefit from breaks, his bladder has been messed up for months and I fear for him some of the damage is truly permanent where in my own caze, a 7 day break will have my bladder return almost to pre ketamine awesomeness and I have often enough used amounts most people consider to be very insane (weeks of daily use of 3-5 grams a day in the summer and since then just weekend binges but often 10 grams in a weekend and those aren't the most insane weekends either, tolerance is evil).
Either way just use ketamine incidentally, like twice a month or less at most; never use more then a gram in a night or so and drink a lot of water. Water helps, the shorter the nor-ketamine stays in the bladder the less damage it does. Dehydration + a lot of ketamine + some stimulant for more dehydration can mean messed up bladder after one night but 3 grams of ketamine a day for 4 days when drinking loads and loads of water and taking good care of the body can have you symptom free afterwards if lucky, I however do not recommend such amounts, just saying that water really makes quite a difference. Be safe and avoid daily or even weekly use (although I doubt half a gram on the saturday evenings would hurt much; it could lead to a more serious habbit as ketamine can be pretty proper fucking addictive, it's the only drug I truly struggle with and the drug that caused me the most pain having sufferd through k-cramps lasting up to almost a week at a time for 15+ times and K-cramps redefine pain, haven't had them in months, cutting down helps
). Also after a month or two of daily usage of serveral grams each day I was peeing blood and even solid matter that appeared to be the inside of my bladder wall. It took only 3 days of no ketamine, proper painkillers (because it hurt a LOT) and patience for that to clear up, never got it that bad again because after that I returned to weekend use only which so far has prevented most issues; only had K-cramps once since then and bladder issues after one weekend of dehydration and too much K; never blood again though. Don't do what I did; I did it out of addiction and ketamine addiction is strange because you are very dissociated 24/7 if you use all the time and that is not a healthy mindset at all.
By the way, using IM would just increase tolerance faster I'd guess which would be considered a bad thing. You want tolerance as low as possible so the amounts you use are as low as possible, much more easily avoiding (serious) bladder issues.
Other then bladder issues there is the risk of K-cramps when doing too much at a time and I'm not excagerating if I say that redefined my concept of pain; the first time I got them I honestly thought I was dying; K-cramps are your gallbladder and related tubes (can't think of the right word; just woke up, just got over opiate withdrawal; I am sorry and I hope I'm clear enough in my explanation) reacting to too much K and while it's not actual damage, it is the most painful experience I have ever been through or can imagen; the only thing that even slightly helps too is more ketamine (or strong opiates; which is about as bad of an idea to treat it with as is more ketamine)
Tl;dr: If you are worried; use only occasionally, like once or twice a month and never too much in a sitting and drink a lot of water. ROA does not matter, all routes can and will cause bladder damage if you simply do too much. Best way to avoid ketamine bladder issues is just avoid a high tolerance; lower doses and occasional usage are extremely mild on the body but once you go past that 'more then a few grams in a day or so' problems do start and they become very serious very quickly.
Sorry for the long post; I have extensive experience with ketamine health issues; both on myself and on people I know having had both K-cramps often and bladder issues to somewhat of a severe degree. I haven't had K-cramps since late september though and my bladder did restore even though I still use ketamine every weekend. Not nearly as much and after the upcomming one month break hopefully just once or twice a month myself too but I have a lot to write on the subject so when it comes up I tend to do so. I still love ketamine even though what I had it do to me, not counting lsd or dmt it is still my favorite drug and I crave it CONSTANTLY. All the time. Every time. It is always on the back or front of my mind. If souls existed, I'd sell mine for ketamine. Ketamine cravings are insane, really all I want is the dissolve in the dissociative space...
