@Zinnypig Water intake increased a bit. He's been doing better lately. The antibiotics did quite a number on him and we had to take breaks. No way to tell if he was even on the right medications, given that there wasn't a clear and sustained improvement and no lab tests were done. He did worse overall on Doxycycline. Baytril mixed with minimal simple syrup seemed to work best to help dry up his snot. He has had chronic dental issues, so I check his incisors weekly. His sinus infections seem connected to issues he's had with breakage and decay in his top incisors. Hoping he doesn't need a dental trim, but keeping a close eye in case he does. He's been off Baytril for a week now, finally, and has been pretty stable. Still runny nose and sneezing, but definitely getting by, especially considering chronic dental issues. Pellets prior to antibiotics and probiotics 1.5hrs after antibiotics have been key for helping his tummy cope along with only giving gassy/sugary veg after probiotics. Garden Select Guinea Pig Food (pellets) by Oxbow helped improve his poop too.
Just found some concerning links between the antibiotics he has been on and eye health, including vision loss and blindness in cats and humans. Seems much less studied (if at all) in guinea pigs... His vision has gotten worse and his iris and pupils look different in both eyes - misshapen pupils and darker irises than before. He's older and had an eye injury, so I think the changes didn't raise red flags to me until my friend questioned if there could be a connection to the antibiotics. His right eye had an injury (surface scratches and small ulceration) that was healing quite well. Now, he's lost all vision in the right eye, which makes him nervous at times, since he can't see what is happening on his right side and gets startled more easily because of that.
His appetite and energy levels/mood have been good these days, so that is good. He eats well as long as certain veggies are cut up. LOVES basil and most stemmed veggies, especially.
His vet has Baytril as needed and Metacam on his file if needed and a note to come in for a dental trim any time without need for an additional charge for physical exam. His condition has been chronic at this point and the vet is on board with that plan. Metacam does also carry risks (head tilt/balance, stomach ulcers, kidney problems), so that's really just a last resort if chronic dental issues (and possible arthritis in his hips) become a problem for his quality of life.