Can i take pepcid (famotidine) ac if i'm allergic to shell fish?

Yes,: there is not an interaction between the two. Actually there is very slight benefit of taking pepcid in shellfish allergy. Because it blocks histamine (but not at the places where MOST of the allergy occurs) there is potentially some small effect of pepcid. Better, though, is taking an anti-histamine ... such as benedryl or claritin (loratadine). Of courrse avoiding shellfish is really the best policy.

Prophylaxis: It depends on the severity of the allergy. Some people try to use pepcid (famotidine) before eating shellfish to ward off allergic symptoms. Pepcid (famotidine) is a histamine blocker so it may be used for treatment of allergic reactions when they occur but I awoud advise you not to rely on their ability to prevent them especially if your shellfish allergy involves airway compromise or any breathing difficulty.

Some help: If you are exposed to fish by accident, then you will be best suited by taking benadryl (diphenhydramine) or another H1 blocker instead of Pepcid AC(this is an H2 blocker). Different antihistamine medication have different antiallergy potential. Remember antihistamine therapy doesn't always prevent allergies from progressing, so you still may need to seek urgent help!