Amitriptyline? Has anyone ever had any experience with it and their cat?

We have a cat with an anxiety problem. We've used the Feliway diffusers to some degree of success, but he continues to have anxiety attacks. He will literally shake for 30 minutes or more, ears twitching all directions, and be super jumpy. He's frightened, but for no apparent reason. He was somewhat this way as a small kitten, but now he is about a year and a half old and more nervous than ever. He was neutered at 4 months old, goes to the vet every 6 months, and is in perfect health otherwise. Is this medication a safe option for him?