I have a big, somewhat portly tabby with a history of constipation. He's never needed an enema, but lactulose, pumpkin (which he won't eat
) and Metamucil have all been on the menu. He's been fine for a long time now. My cats do eat quality kibble, but they also get canned morning and night (and sometimes in between). An all-canned diet is optimal, so their gut is well hydrated.
Even if the problem is structural (megacolon), it can still often be managed by keeping tabs on the situation and acting quickly. This sometimes means lurking around the litter box
I never use any remedy for longer than necessary. You want their systems to function normally; the remedy is a kick-start (excluding really severe cases which may require prolonged treatment. But even then, try to get whatever dose and/or frequency down to a minimum, while still remaining effective).
So since he won't eat pumpkin, Badger gets two or three days of Metamucil mixed into his wet food - maybe a half-teaspoon - and when things get rolling again, I stop. Lactulose I reserve for when nothing else works (he hates the taste).
I would say don't panic, watch his diet and his litterbox activity and if he seems to be straining, dose him (one remedy at a time). All other things being equal (no fever, no loss of appetite, no blood in his stool), it is more a management problem. Or, maybe in your cat's case, it's a one-off? Time will tell.