Ask the Pharmacist

Q.   My kidney specialist mentioned I need to watch my intake of phosphate. Why is that and what can I do about that?

A.   People that suffer from chronic kidney disease are unfortunately unable to rid the body of phosphate. This in turn can lead to high blood levels of phosphate in the body which can then make you more likely to be diagnosed with hypocalcemia (i.e. low calcium blood levels which makes your bones more susceptible to a fracture), hyperparathyroidism, renal bone disease and vascular calcification. It has also been linked to a higher mortality. To help prevent this occurrence, it is best to maintain a low phosphorous diet by limiting the consumption of the three main sources of dietary phosphorous.

First, there are natural phosphates that are found in certain foods such as fish, meat, dairy and grains. Second, some foods have phosphates added to them during the manufacturing process such as processed foods, fast foods, ready-to-eat foods and dark colas. Lastly, there are phosphates that are found in supplements and some medications. It is believed that natural phosphates such as the ones found in the foods mentioned above are not as bioavailable (not as readily absorbed) and do not have nearly the same impact on our blood levels as the other forms of phosphate that we consume. Therefore, you do not have to strictly avoid those foods as they may provide you with other health benefits.

Given how prevalent fast food is in our diet perhaps it is not surprising to learn that most people who have chronic kidney disease need to rely on phosphate binders to help control the phosphate levels in their body. A simple, inexpensive phosphate binder is calcium carbonate which many people can find readily as a supplement or in the stomach remedy area (Tums). It requires regular dosing of 2 to 3 tablets with each meal (not to exceed 1500mg of elemental calcium each day) and because it is a calcium supplement, it can lead to hypercalcemia, or too much calcium which may be associated with vascular calcification. Due to this fact, even if calcium levels are not a big concern for you, it is recommended to limit the dose of calcium-based phosphate binders.

There are a few other alternatives that can be used instead. Ideally, the phosphate binder should be well tolerated and not be affected by the pH (or level of acidity) in your gut, all while being inexpensive. Aluminum hydroxide suspension is an effective yet inexpensive choice and it does not affect the calcium level in the body.

Unfortunately, it is known to be constipating which, in severe cases, can lead to fecal impaction. If that doesn’t steer you away from taking aluminum hydroxide on a regular basis, perhaps the risk of aluminum toxicity, dementia, encephalopathy, osteomalacia and anemia will. Due to these potential long-term effects, it is suggested to only use aluminum containing binders on a short-term basis.

Other phosphate binders to consider are sevelamer calcium (Renvela) or sevelamer hydrochloride(Renagel), since they will not raise calcium levels in the body. Sevelamer carbonate is preferred as it is not associated with a side effect known as metabolic acidosis while its counterpart is. Both however, may bind with fat soluble vitamins such as vitamins A, D, E and K and therefore it is important to take a vitamin supplement and to take the binders at a different time of the day. A last choice for a phosphate binder is lanthanum carbonate (Fosrenol) which is very convenient with its dosing schedule of one chewable tablet per dose but it is also very costly.

As you might have guessed with the name phosphate binders, not only does it bind with phosphate to reduce the phosphate level in the body, but there is also a risk of that they will “bind” with other medications and thus prevent their absorption. It is therefore highly recommended to take other medications at least 1 hour before or 3 hours after taking any of these binders.