Sorry to hear about Schroder. One question, why did your veterinarian switch from Rimadyl to Deramaxx? Was there a 'wash out' period of two weeks prior to the switch?
My thoughts are that either 1) the signs may be related to the medication switch or 2) it is unrelated. To rule out the later, I would recommend that you contact your vet as you have planned. If it is the former, I will explain some information for general switching of the this medication class but would still recommend you contact your vet.
Deramaxx, Rimadyl, Metacam, Previcox, Zubrin, Ketoprofen are all part of a drug class called NSAIDs (Non Steroidal Anti Inflammatory Drugs). There are many examples in human medicine (>30) which include: aspirin, tylenol, advil, celebrex etc... NSAIDs interact with two receptors: Cox 1 and Cox2. Cox 2 is related to pain and inflammation. This is why the medications help relieve these symptoms. Cox 1 receptors are involved with homeostasis (keeping the good things running in your body) such as kidney blood flow, stomach mucous production and stomach acidity. The goal of all companies is to create a NSAID that does not touch Cox1 - so far the companies have made ones that are more 'Cox-1' sparing than before but there are none that are completely without Cox-1 effects.
Why do we care about Cox-1? For a variety of reasons, but in this case it is important to realize that the 'pain' effects (Cox-2) are affected by the NSAIDs for 12-24 hours. The medication however can have lasting effects on Cox-1 for up to two weeks (this is a common period accepted by most specialists). When you combine any two NSAIDs - their negative effects on Cox-1 can be anywhere up to TEN TIMES worse than if you just doubled the dose of one of the drugs by itself. While each combination is different, the take home point is that there can be interaction which is worse when combined. When switching from one NSAID to another it is generally recommended to have a two week 'wash out' period. Obviously for reasons of patient comfort, this is not always done. Usually you can switch from one to another with little problem. So, if a vet does not do this, it is not necessarily wrong. Immediate switching can cause some problems and the most common is stomach upset. For mild problems, this can often be treated with pepcid (famotidine). For schroder I assume he is approximately 50lbs? For a 50lb dog, a dose of famotidine is 20mg by mouth every 24 hours. Please check with your veterinarian prior to administering this however!
Now, which NSAID is the BEST??! If there was one which worked best, there would not be so many on the market. There are some that have higher safety ranges and may be more Cox 1 sparing. But importantly, one may work great in one dog and poorly in another. Just like people - most people like advil for one thing, aspirin or pamprin for another. Also some come in various forms (chewable, non chewable, honey flavored liquid or dissolving tablet). So the big question is which one is best for you and your pet. This will be determined on three factors: 1) one that makes the pet feel better, 2) a form that the owner finds compliance easy, 3) one that does not negatively interact with the pet (this should be determined by blood testing with your veterinarian).
FWIW - there was a head to head test on Deramaxx, Rimadyl, Metacam and Previcox. Please note that the test was paid for by the makers of Previcox however usually when the data does not add up to what the makers like - they just do not release the information (as opposed to 'tampering' with data). Thus previcox came out with highest safety ranges. Also the oral tablet takes faster action than Rimadyl injectable. Metacam was the next safest, then Rimadyl and last Deramaxx. Safeness was determined by lowest number of side effects add a higher than normal dosing along with range of safety. As far as pain relief they all had similar effects with metacam and previcox as slightly higher. What was interesting was that the previcox longer term (over 2 months) had better pain effects than all the others. With that said, because of higher cost and it being a newer medication - it is not seen widely. I carry it but honestly prescribe Metacam the most. I like it because the liquid form is highly palatable and easy to dose with weight. I also have patients on Rimadyl (one of my own dogs - didn't switch her from it because she has always responded so well to it) and also patients on Deramaxx.
Final thought on human NSAIDs - please do NOT use these alone or especially in conjunction with the dog NSAIDs. Aspirin has long been used in dogs - I wish it was not used at all for pain. The dose we use to interfere with platelet function (where we want to help stop clot formation) is TEN times LESS than the dose needed for relief of pain. There was a study done that suggests that all dogs on pain doses of aspirin have some form of intestinal bleeding regardless of how 'normal' they are acting. As I am sure the other members here will also recommend is that to use the concurrent use of glucosamine, chondroitin, MSM and Omega 3 fatty acid (especially those that have high levels of EPA in them). If all of these are not enough and no surgery is indicated by your veterinarian, then tramadol is a great, safe, inexpensive pain medication that CAN be given with NSAIDs.
Good luck with Schroder! Let us know what your veterinarian says!