How do phosphate binders actually work?

A phosphate binder is a molecule that grabs onto phosphorus in your stomach and intestine and forms a compound your body can't absorb. That bound phosphorus leaves in stool instead of entering your blood.

Which is why timing decides whether the pill works at all. Taken with the first bites of a meal, the binder is mixed in with the food it's supposed to grab. Taken an hour later, the phosphorus has already been absorbed and the dose is largely wasted.

Different binders use different partners — calcium, lanthanum, iron, or a resin like sevelamer — and one drug class (tenapanor) works differently again, by tightening the gut wall so less phosphorus slips through.