Laryngeal Paralysis

Anyone here with a lab that has this condition? My 12yo boy, Henry, was just diagnosed. The prescribed Doxepin and he's been on it for 3 days now and I'm really worried about the side effects, having had an ad worse reaction to a tricyclic antidepressant myself.

Tonight he started whining and trying to howl, pacing, drooling and panting. He seems very agitated. He's also been much more clingy than usual. I'm worried they prescribed too high a dose. He's 25kg and they prescribed 100mg twice a day. That just seems like way too much to me, but I don't know anything.

Would appreciate any advice or your experiences with this drug, if it actually does anything and whether it is just too much.

I have a message in to my vet and am just waiting for a call back.