Sodium Polystyrene Sulfonate works by swapping sodium for potassium in your intestines — the potassium sticks to the resin and leaves your body through your stool, lowering the amount of potassium in your blood.

That's the short version. If you want to understand exactly what's happening in your body when you take this medication — and why your doctor chose it — keep reading. We'll explain the mechanism of action in plain language, without the medical jargon.

What It Does in Your Body

Sodium Polystyrene Sulfonate is a cation-exchange resin. Think of it like a sponge that's already soaked with sodium. When it travels through your intestines, it releases its sodium and grabs onto potassium instead. This process is called ion exchange.

Here's how it works step by step:

1. You take the medication — either by mouth (mixed with liquid) or as a rectal enema.
2. The resin reaches your intestines — primarily the large intestine (colon), where most of the exchange happens.
3. Sodium is released, potassium is captured — The resin gives up its sodium ions and binds to potassium ions that are present in the intestinal fluid.
4. The potassium-bound resin is eliminated — You pass it out in your stool, taking the excess potassium with it.

Each gram of Sodium Polystyrene Sulfonate can exchange roughly 1 mEq of potassium in your body. So a standard 15 g dose removes approximately 15 mEq of potassium.

It's Not Perfectly Selective

One important thing to understand: Sodium Polystyrene Sulfonate doesn't only grab potassium. It can also bind to calcium and magnesium in your intestines. This is why your doctor monitors your electrolyte levels while you're on this medication — to make sure calcium and magnesium don't drop too low.

For more on what this means for side effects, read our side effects guide.

It Stays in Your Gut

Unlike many medications, Sodium Polystyrene Sulfonate is not absorbed into your bloodstream. It works entirely within your digestive tract. This is why it has relatively few systemic side effects — but it can cause gastrointestinal issues like constipation, nausea, and in rare cases, bowel damage.

How Long Does It Take to Work?

Sodium Polystyrene Sulfonate is not a fast-acting medication. Here's what to expect:

• Oral dose — Effects begin within a few hours, but it may take 6 to 24 hours to see meaningful reductions in blood potassium levels.
• Rectal enema — May work slightly faster since it's delivered directly to the colon, but onset is still measured in hours, not minutes.

This is important: if your potassium is critically high and causing heart rhythm problems, Sodium Polystyrene Sulfonate alone isn't fast enough. In emergencies, doctors use IV calcium (to protect the heart immediately), insulin with glucose (to shift potassium into cells quickly), and then Sodium Polystyrene Sulfonate to remove the excess potassium from the body over the following hours.

How Long Does It Last?

The potassium-lowering effect of a single dose lasts roughly 4 to 6 hours. That's why many patients take multiple doses throughout the day — or a larger once-daily dose, depending on their doctor's instructions.

The resin itself passes through your system and is eliminated in your stool. There's no buildup in your body over time.

Your doctor will check your potassium levels with blood tests (usually a basic metabolic panel) to determine how often you need to take it and when it's safe to stop or reduce the dose.

What Makes It Different From Newer Alternatives?

Sodium Polystyrene Sulfonate has been around since the 1950s. It works, and it's affordable — but it's not the only option anymore. Two newer potassium binders have entered the market:

Patiromer (Veltassa)

Approved in 2015, Patiromer uses calcium instead of sodium for the ion exchange. It's more selective for potassium (meaning it binds less calcium and magnesium), has fewer GI side effects, and is generally better tolerated. However, it costs $600-$900/month compared to under $20 for generic Sodium Polystyrene Sulfonate.

Sodium Zirconium Cyclosilicate (Lokelma)

Approved in 2018, Lokelma is a non-polymer crystalline compound that traps potassium in its crystal structure. It's more selective for potassium than Sodium Polystyrene Sulfonate, works faster (onset within 1 hour), and is well-tolerated. It costs $500-$800/month.

So why do doctors still prescribe Sodium Polystyrene Sulfonate? Mainly because of cost and availability. It's been used safely for decades, it's available as an inexpensive generic, and it does the job for most patients. For a full comparison, see our guide on alternatives to Sodium Polystyrene Sulfonate.

Why Does Your Doctor Monitor Your Labs?

Because Sodium Polystyrene Sulfonate removes electrolytes from your body — not just potassium — your doctor needs to track several blood levels:

• Potassium — To make sure it's coming down (but not too far). Hypokalemia (low potassium) is dangerous too.
• Calcium — The resin can bind calcium, potentially causing low levels.
• Magnesium — Same concern as calcium.
• Sodium — Since the resin releases sodium, it could theoretically contribute to sodium overload in patients who are fluid-restricted.

Regular blood work is essential while taking this medication. Don't skip your lab appointments.

Final Thoughts

Sodium Polystyrene Sulfonate works through a straightforward mechanism: it trades sodium for potassium in your gut and carries the potassium out in your stool. It's not fancy, it's not fast, but it's effective and affordable.

Understanding how it works can help you take it correctly and recognize potential issues. If you have questions about whether this medication is right for you, talk to your doctor or nephrologist.

Need to fill your prescription? Use Medfinder to find Sodium Polystyrene Sulfonate in stock at a pharmacy near you. For more information, explore our guides on uses and dosage, drug interactions, and saving money on your prescription.