Thanks for the answers to my questions although I'm sorry I was off my computer when you responded back.
I, too, am concerned about his symptoms since it sounds as if he may be a little worse than he was or at the least, he doesn't sound as if he's improving, unfortunately. The various drugs that you mention are ones which I would have used in this situation in case you were wondering.
1. As to the drugs that he's taking, every vet is different, of course, in terms of what they prescribe. Tramadol has quite a wide dosage range which means that this drug can be increased, if necessary. 25 mg is at the low end of the range for a dog this size; he could be given 50 mg up to three times a day...or even 100 mg three times a day although I wouldn't go this high initially.
If his pain isn't being well controlled at 25 mg, then I'd increase it if he were my patient.
2. The dose of Pred is a bit on the higher side from what I'd have recommended for his body weight so there wouldn't be any advantage in increasing it.
3. Gabapentin also has a wide range of dosages; if he were my patient, the dose I'd have prescribed would be 50-100 mg twice a day although it could also be increased, if necessary. He may already be taking the appropriate dosage amount but I just wanted to mention it to be complete.
Sedation and balance issues are probably the most likely adverse effects seen in dogs when this drug is given so it's possible that his being "wobbly" is secondary to this drug although the muscle relaxant may also be at fault. Starting the dose at the lower end of the range and increasing with time may alleviate these effects.
I wouldn't worry too much about him not urinating or defecating although he may have done so since you posted your question about him.
At this point, without additional testing, medical treatment as he's receiving is the best course of action. Restricting his movement will also be critical although he may be doing this himself.
If he doesn't start to respond to his medication within the next few days and/or he continues to worsen, then I'm sad to say that his prognosis isn't good for a return to function. However, if only his hind legs are affected and his pain level can be controlled, then he may be a good candidate for a wheel chair...if this is something you might consider. I've seen a number of dogs with weakness or complete paralysis in their back legs do amazingly well with wheelchairs although I do understand they may not be for every dog or every owner. But, I did want to at least mention the possibility as something that you might want to consider if it comes to that.
I hope this helps although, again, my apologies for the delayed reply to you. Deb