Phosphorus binders are medications for individuals with advanced kidney disease, particularly those undergoing dialysis. Their primary function is to lower the amount of phosphorus the body absorbs from food, helping pass the excess out of the body before it enters the bloodstream. For people on dialysis, dietary changes alone are not enough to control phosphorus levels, making these medications a routine part of treatment.
The Role of Phosphorus in Kidney Disease
When kidneys function properly, they filter excess minerals like phosphorus from the blood, which is then removed through urine. In chronic kidney disease (CKD), the kidneys lose this ability, causing phosphorus to accumulate in the blood, a condition known as hyperphosphatemia. Dialysis can remove some phosphorus, but it is insufficient to keep levels within a safe range, especially considering the phosphorus content in many foods.
Persistent high phosphorus levels contribute to a complex condition called chronic kidney disease-mineral and bone disorder (CKD-MBD). This disorder disrupts the normal balance of calcium and phosphorus in the body. The body attempts to correct the high phosphorus by pulling calcium from the bones, which weakens them over time. This process increases the risk of bone pain and fractures.
Excess phosphorus and calcium can form hard deposits in soft tissues, including blood vessels. This process, known as vascular calcification, causes arteries and veins to stiffen, which can impede blood flow. It is associated with a higher risk of cardiovascular events like heart attack and stroke, which are significant causes of mortality in people with CKD.
How Phosphorus Binders Work
Phosphorus binders function locally within the gastrointestinal (GI) tract and are not absorbed into the bloodstream. They work like a magnet, binding with phosphorus from food while it is in the stomach and intestines. This action forms an insoluble compound that cannot be absorbed by the body.
The binder and the captured phosphorus then move through the digestive system and are eliminated from the body in the stool. This process effectively prevents dietary phosphorus from ever entering the bloodstream, helping to maintain safer levels in the body.
Types of Phosphorus Binders
Phosphorus binders are grouped into categories based on their primary component. The selection depends on an individual’s specific health needs, including their serum calcium levels and other co-existing conditions.
Calcium-Based Binders
Calcium-based binders, such as calcium carbonate and calcium acetate, are among the most commonly used types. They are effective at lowering phosphorus and are relatively inexpensive. However, a consideration is that the body can absorb some of the calcium, which can lead to elevated calcium levels in the blood, or hypercalcemia. Since high calcium can contribute to vascular calcification, calcium levels must be monitored closely in patients using them.
Non-Calcium-Based Binders
To avoid the issue of calcium loading, several non-calcium-based binders have been developed. Sevelamer is a polymer that binds phosphate. An added effect of sevelamer is its ability to bind bile acids, which can help lower LDL (bad) cholesterol levels. Its primary drawbacks are gastrointestinal side effects like nausea and a high pill burden for some patients.
Lanthanum carbonate is another non-calcium option that comes in a chewable tablet or powder form, an advantage for those who have difficulty swallowing pills. It is a potent binder, often allowing for a lower number of pills per day compared to other types. Although rare, there is a potential for lanthanum to deposit in tissues like bone and the liver over long-term use, though clinical toxicity has not been clearly demonstrated.
Iron-Based Binders
Iron-based binders, including sucroferric oxyhydroxide and ferric citrate, are more recent additions. These medications bind phosphorus and have the dual benefit of providing supplemental iron, which can be absorbed and help manage the anemia that is also common in kidney disease. A common and harmless side effect is the darkening of the stool color due to the iron content. Diarrhea can also occur but is often temporary.
Proper Administration and Common Side Effects
For phosphorus binders to be effective, the medication must be in the digestive tract at the same time as food to bind with the phosphorus it contains. This means binders should be taken within five to ten minutes before or immediately after meals and snacks. If a meal is skipped, the dose of the binder should also be skipped, as there is no dietary phosphorus to bind.
Phosphorus binders can cause side effects, most of which are gastrointestinal. Common issues include constipation, nausea, diarrhea, and gas. These side effects can be a reason some individuals struggle to take their medication as prescribed. Managing them often involves a conversation with a healthcare provider and dietitian.
For constipation, a doctor might recommend adjusting the diet to include more fiber or prescribing a stool softener. If nausea is an issue, experimenting with the exact timing of the dose in relation to the meal might provide some relief. Patients should communicate any side effects they experience to their healthcare team so that adjustments can be made, which may include trying a different type of binder that is better tolerated.