You want to buy Grapefruit-Seed-Extract by NutriBiotic - they are the original developers. I have liquid (very bitter but can be added to citrus juice). I have also used their capsules. Follow directions on bottle. I get mine at the health food store.
For anyone who has allergies get the pills w/echinacea added -- it's great and clears up the sinuses, but if you have nose parasites, that's a different story.