The tylan is an antibiotic. It was original used for chickens. You can buy it on Amazon for $40. It will last a long time. My vet told me no long term effects. At one point, Lexie was on it for 3 years. No side effects and she has a very sensitive tummy. It was the only thing that helped her with mushy poo.
Just my opinion, since the tylan helped him before, it would be worth to try again.