Phosphorus binders, also called phosphate binders, are medications taken to reduce the amount of phosphorus the body absorbs from food. Available in forms like tablets, powders, and liquids, they are used by individuals with health conditions that impair the body’s natural ability to filter this mineral.
The Role of Phosphorus Binders in the Body
Phosphorus binders are used to treat hyperphosphatemia, or high levels of phosphate in the blood. This condition is a frequent complication for people with chronic kidney disease (CKD) because their kidneys can no longer effectively remove excess phosphorus. When kidney function is compromised, even normal dietary phosphate intake can lead to elevated blood levels. Healthy kidneys are responsible for balancing this mineral, which is necessary for building strong bones and helping cells produce energy.
Unmanaged hyperphosphatemia leads to significant health problems. Excess phosphorus pulls calcium from the bones, making them weak and brittle. This imbalance contributes to mineral and bone disorder, increasing the risk of bone pain and fractures.
The consequences of high phosphorus extend to the cardiovascular system. The calcium that is drawn from the bones can form deposits in soft tissues, including on the walls of blood vessels and the heart. This process, known as vascular calcification, causes arteries to harden and stiffen. This condition raises the risk of serious cardiovascular events, including heart attack and stroke, and is associated with increased mortality in patients with CKD.
How Phosphorus Binders Work
Phosphorus binders function locally within the gastrointestinal (GI) tract to prevent dietary phosphorus from being absorbed into the bloodstream. These medications are not meant to be absorbed by the body in any significant amount. Instead, they travel through the stomach and intestines, where they intercept the phosphorus released from food during digestion.
The mechanism can be thought of as a magnet or a sponge. The active ingredients in the binders attract and bind to phosphorus molecules, forming a new, insoluble compound. This compound is too large to pass through the intestinal wall and enter the bloodstream.
Once the phosphorus is locked into this new form, it continues through the digestive system. The bound phosphorus is then eliminated from the body as part of the stool. This process blocks dietary phosphorus from reaching the blood, helping to maintain safer levels.
Common Types of Phosphorus Binders
There are several categories of phosphorus binders, which are generally grouped into two main classes: those that contain calcium and those that do not. The selection of a binder depends on a person’s specific medical needs, including their serum calcium levels and the stage of their kidney disease.
Calcium-Based Binders
Calcium-based binders are a common choice and include medications like calcium carbonate and calcium acetate. Calcium carbonate is widely available and is also found in common antacids. These binders work effectively by using calcium to bind with phosphorus in the gut.
A consideration with these binders is the amount of calcium they add to the body. Since some calcium can be absorbed, there is a potential for elevating blood calcium levels, a condition known as hypercalcemia. This can contribute to vascular calcification, so blood calcium levels are monitored.
Non-Calcium-Based Binders
This class of binders was developed to avoid adding to the body’s calcium load. Common types include:
- Sevelamer: A polymer available as sevelamer carbonate and sevelamer hydrochloride that binds phosphorus in the intestines without containing calcium or metal.
- Lanthanum carbonate: A chewable tablet that uses the element lanthanum to bind with dietary phosphorus.
- Iron-based binders: A newer category including sucroferric oxyhydroxide and ferric citrate that use iron to bind phosphorus and may increase the body’s iron stores.
Proper Administration and Side Effects
For phosphorus binders to be effective, their administration must be timed correctly. These medications need to be taken with food, either just before, during, or immediately after a meal or snack. This timing is necessary because the binders need to be present in the gastrointestinal tract at the same time as the food to bind with the phosphorus that is released during digestion. Taking a binder on an empty stomach will not have the intended effect, as there is no dietary phosphorus to bind.
The dosage often varies depending on the size of the meal; larger meals may require more binders than smaller snacks. If a dose is forgotten, it may be helpful to take it up to 30 minutes after eating. If more time has passed, it is better to skip the dose and wait until the next meal.
The most frequently reported side effects of phosphorus binders are related to the gastrointestinal system. These can include constipation, diarrhea, nausea, and gas. Some side effects are specific to the type of binder; for example, iron-based binders can cause stools to appear dark or black. Anyone experiencing persistent or bothersome side effects should discuss them with their doctor, as adjustments to the type or dose of binder may be possible.