I agree with chico that there are foods with much better ingredients than Hill's. Prescription diets are a big scam and vets really shouldn't be giving out nutrition advice, given their lack of knowledge on the subject. Here are the ingredients for S/D (which is typically "prescribed" for cats with struvite crystals in their urine, by the way):
Pork By-Products, Pork Liver, Water, Chicken Fat (preserved with mixed tocopherols and citric acid), Rice, Corn Starch, Ground Whole Grain Corn, Calcium Sulfate, Powdered Cellulose, DL-Methionine,....
Heavy on the plant matter, low on quality protein. Completely inappropriate ingredients for an obligate carnivore, but especially one with intestinal issues. I strongly suggest finding a grain-free canned food like the Wellness
that chico mentioned (there's a store locator on their website), or something with a novel protein source like Innova Evo 95%
venison or duck, or Nature's Variety Instinct
(which also comes in rabbit and lamb). The ultimate would be a raw food diet, which has saved the life of many a cat suffering from bowel inflammation. I urge you to read this link: http://www.catnutrition.org/index.php
And here is more info on feline nutrition in general: www.catinfo.org
Also just want to add a warning about the Metacam. Has your cat had blood work and a urinalysis done to check how his kidneys are doing? Metacam has been known to cause kidney damage in some cats and should never be used in cats with pre-existing renal insufficiency. Buprenex or Fentanyl are safer choices.