Hi there I'm not suggesting you should be second guessing your vet,
but they have often been known to the wrong!
if Panda. Was my pig I would be asking your vet to get in touch with the knowledgeable Guinea pig vet like Simon Maddox
http://www.catandrabbit.co.uk/html/contact_us.html to discuss Panda's dosage protocols. He is very approachable and always willing to talk to all the vets regarding Guinea pigs.
Regarding the scar tissue, a few years ago a branch of the rspca successfully treated a pig with respiratory problems with a combination of baytril and septerin , but they would not put him out for adoption because his lungs were badly scarred, and he had a chronic weepy eye as a result of this.
And it was decided by them to put this pig to sleep, As long-term vet bills would be likely
luckily one of their volunteers, got in touch with a friend who in turn got in touch with me, and I agreed to take over the Vet bills and long term care and maintenance of this piggy,
Apart from his weepy eye's, he did experience breathing difficulties if there is a high level of dust in the air, for this reason and also for the well-being of my other pigs, I installed HEPA the air filters in my pig room, and devise my own dust hay extraction system ,
since I have kept a close watch on the dust levels in my pig room, the pig in question, plus another one that would hoot and wheeze like an old man, are now totally fine .
I don't know whether panda is an indoor or outdoor Piggie, but maybe keep an eye to the dust levels
Just a thought
I really hope you manage to fix pander