When to Take Phosphate Binders, and What to Keep Away From Them

People on dialysis take a median of 19 pills a day, and phosphate binders make up about half of them. That’s from a 2009 study of 233 patients at three US dialysis units. When that many pills share a day, when to take phosphate binders, and what to keep away from them, affects how much of the rest you actually absorb.

I have stage 5 kidney disease and I’m on hemodialysis, so my blood work tells me every month whether my routine is doing its job. For months I took my iron with meals, right next to my calcium. I thought I was careful. My own app caught it, which is an awkward way to find a flaw in a routine you designed.

The meal wasn’t the problem. The calcium beside it was. This piece covers the easy part (binders go with food) and then the part most guides leave out: what each binder’s FDA label says to keep away from it. The labels don’t all agree, which is the best argument I know for taking your own list to a pharmacist.

When should you take phosphate binders?

With meals. Every binder label I read says so, with small differences in how you swallow it:

• Sevelamer (Renvela, Renagel): with meals. Renvela label.
• Calcium acetate: with each meal. Calcium acetate label.
• Lanthanum (Fosrenol): with or immediately after meals, chewed or crushed completely. Fosrenol label.
• Ferric citrate (Auryxia): with meals, swallowed whole. Auryxia label.
• Sucroferric oxyhydroxide (Velphoro): with meals, chewed or crushed. Velphoro label.

The reason is simple. A binder catches the phosphorus in the food you’re eating and carries it out of your body instead of letting it into your blood. That’s how the NIDDK describes them, as part of treating mineral and bone disorder in kidney disease. A dietitian writing for the Renal Support Network puts the usual window at within minutes before, or right after, meals and snacks.

Do phosphate binders work without food?

They’re built to work on a meal. The Fosrenol label says that to bind dietary phosphate, it must be taken with or immediately after meals. If you forget a dose or skip a meal, ask your dietitian what they want you to do. Don’t improvise by doubling up later.

Why a binder changes the timing of everything else

A binder is designed to grab things in your gut. Phosphorus is the target, but some medicines get caught too, and then less of them reaches your blood. Every binder label I read has some version of the same warning: if absorbing less of another oral medicine would matter for its safety or effect, consider taking the two at different times.

The sevelamer and calcium acetate labels both tell prescribers to counsel patients to take such a medicine at least 1 hour before or 3 hours after the binder. Then each label names specific drugs that need more, and that’s where it gets interesting.

What shouldn’t phosphate binders be taken with?

Here is what each label says about the medicines that come up most: an antibiotic (ciprofloxacin), a thyroid pill (levothyroxine) and iron. These are the labels’ own figures, not a schedule for you. Your pharmacist sets yours.

From each product’s current FDA label on DailyMed, linked in the sources below. The Synthroid and Cipro labels add their own rules, covered next.

Can phosphate binders be taken with antibiotics?

Ciprofloxacin is the antibiotic the labels name most. A single dose of sevelamer cut its absorption by about 50% in healthy volunteers, and so did calcium acetate and Fosrenol in their own studies. Auryxia cut it by about 45%, but its label notes there was no interaction when the two were taken 2 hours apart.

The Cipro label has a rule of its own: take it at least 2 hours before or 6 hours after sevelamer, lanthanum, or any product containing calcium, iron or zinc. Velphoro’s label, meanwhile, lists ciprofloxacin among the drugs it can be taken with. Velphoro contains iron. So the two labels don’t line up, and that’s exactly the kind of question a pharmacist should settle, not you or an app.

One more detail worth knowing: for short courses of these antibiotics, the Fosrenol label suggests prescribers consider dropping the binder doses that would fall near the antibiotic. That’s a call for your doctor, never one to make on your own.

Phosphate binders and levothyroxine

The Synthroid label lists phosphate binders by name (calcium carbonate, ferrous sulfate, sevelamer and lanthanum) and says to take levothyroxine at least 4 hours apart from them. It also tells patients to keep iron and calcium supplements and antacids 4 hours away.

The binder labels give different numbers. Fosrenol cut levothyroxine absorption by about 40% and its label says 2 hours either side. Velphoro says at least 4 hours before. Sevelamer’s label doesn’t give a number but reports raised TSH, a thyroid blood test, in people taking both. If you take a thyroid pill and a binder, ask which gap your team wants.

Phosphate binders and iron

This one surprised me. Sevelamer’s label lists iron among the drugs whose absorption sevelamer did not change in studies. So a sevelamer and iron clash isn’t something the label reports.

Two binders are iron themselves. Auryxia’s label says its iron is absorbed, that ferritin and iron saturation rose in trials, and that people also getting IV iron may need that IV iron reduced or stopped. And on dialysis, you may be given IV iron during treatment, according to the NIDDK. If you take Auryxia and an iron pill, it’s fair to ask whether you still need both.

Can you take iron and calcium together?

This is the mistake I made, and it’s behind a question that comes up over and over in my dialysis support groups: “Why isn’t my iron going up? I take it every day.”

In a 1991 study of 126 people, 165 mg of calcium in a meal, given as milk, cheese or a calcium salt, cut iron absorption from that meal by 50 to 60%. Larger amounts did about the same. That’s a single-meal effect.

Over the long run the picture is softer. A 2010 review found that studies giving people more calcium for long periods showed no change in their iron status, and suggests the body may adapt. So I won’t tell you that moving my iron fixed my numbers. I’ve moved the doses apart and I’m waiting on my next labs.

What about taking iron with food? For most people, MedlinePlus says iron is usually taken with food or right after a meal. The catch on dialysis is that meals are exactly when the binders go in, and some of those are calcium. If your binder is calcium acetate, its label also tells patients to avoid calcium supplements, including calcium-based antacids. There’s more on how the two compete in our calcium and iron pairing guide, and on each mineral in our iron and calcium pages.

Questions to take to your pharmacist

None of this is a reason to move a dose on your own. It’s a list of good questions. These are the ones I’d bring:

• Which binder am I on, and does its label name anything else I take?
• If I’m prescribed an antibiotic, should my binder doses move around it?
• Does my thyroid pill need 4 hours from my binder, iron and calcium, or 2?
• Should my iron go at a different time from my calcium?
• If I’m on Auryxia, do I still need a separate iron pill?
• Is anything I bought over the counter, like an antacid or a supplement, a problem for my kidneys?

Writing it all down helps more than you’d think. Once everything I take sat on one page with a time next to it, the overlap was obvious. Our medication list app page explains how to keep that list in one place.

Where Tavita fits

Tavita is the app I built, and the one that caught my iron mistake. It checks your medicines and supplements against each other and builds a daily schedule around the clashes it knows. For the pairs in this article, the schedule:

• keeps iron and calcium at different times
• keeps levothyroxine away from binders, iron and calcium
• places ciprofloxacin at least 2 hours before or 6 hours after sevelamer, the figures both labels give

There’s also a kidney setting (Mild, Moderate or Severe). Depending on the stage you pick, it flags potassium, magnesium, phosphorus, salt substitutes, electrolyte products, vitamins A and C, and creatine. At Moderate or Severe it blocks a potassium supplement from your schedule.

What it isn’t: a medical device, or a replacement for your pharmacist. It doesn’t set doses, and if your care team gives you a different gap than the app does, follow your care team. Treat it as a second check, and bring what it flags to your next appointment.

It’s free to start and you don’t need an account. The free plan includes one schedule build a month. Pro rebuilds anytime and costs $12.99 a month or $59.99 a year. Our pill reminder then tells you when each dose is due.

Common questions