High Liver Enzymes, Weight loss, Thickened Gallbladder

At the start of December my cat  (Roo) began to vomit regularly and I realized he had lost 1.5lbs (already skinny to begin with). I took him to the vet and his blood work showed high liver enzymes (AST, ALT) and high eosinophiles. All else was normal. He has a history of skin allergies and asthma and has had high eosinophiles in the past. We had an ultrasound which showed hyperechogenic (thickening) gallbladder neck but no sludge. And he had a lymphocyte in his abdomen. All else was normal. For some reason the vomiting has ceased and his energy is fairly normal, maybe a bit more lethargic but still playful and sweet. He continues to eat, drink, and use his litter like normal. Vet recommended Panacure to rule out worms and changing his food to a new protein--he has been on duck/pea and salmon/pea. Vet also recommended an antibiotic, but I'm hesitant since he does not have an infection. I'm really worried about my little guy and want to take care of him. Anyone else had similar issues? Any luck using natural supplement as opposed to antibiotics and steroids?? I appreciate all feedback!