Large dog with cancer. Any recommendations for vets open to euthanasia in Bangkok? TIA!

Have you talked with the vet who made the diagnosis?  In my experience, the only Thai vets who will perform this humane act are those who have treated the pet, know its history and the owner's belief.  

 

I'm from Chiang Mai and just before Covid, I took my cat to Kasetsart University in Bangkok for outpatient cancer treatments not available in Chiang Mai.  When Covid hit, the professors permitted me to admit the cat and encouraged me to return to CM, given my age (the cat was fairly young).  The cat's condition declined and eventually was put on life support (ventilator and kidney dialysis).  Not my wishes, but apparently I'd signed something. The professors were communicating with my CM vet, not me.  The CM vet knew the cat and me very well, and after the third, yes third CPR, she told them "no more, the owner and the cat are Christian no more CPR".  They let the cat pass.  

 

I so regret taking him to Kasetsart or wish I'd taken him earlier.

 

Gamma Exotic will, but they've moved the clinic out from On Nut towards Nong Bon. 

 

I think Sukhumvit Veterinarians on Sukh 51 does as well.

 

But as was already said, they will want a medical history with the animal first.