By David S Goldfarb, M.D.
Director, Kidney Stone Prevention Program, St. Vincents Hospital
Professor of Medicine and Physiology, NYU School of Medicine
Alkalization of the urine is important in cystinuria because it increases the solubility of cystine, meaning that more cystine can be dissolved in a given amount of urine. Alkalization means neutralizing the acid in the urine by adding base. When acid is neutralized there are fewer H+ molecules (also called protons) and the pH rises. pH is a measure of the amount of acid in the urine. Human urine can have pH ranging from about 4 (acid) to about 8 (alkaline). When urine pH rises above 7, cystine becomes much more soluble, so achieving a urine pH of 7.5-8 for a good part of the day is desirable. Measuring and recording your urine pH at various times of the day is very helpful to you and your doctor to show whether you are getting to the desired range.
You can alkalinize your urine by decreasing the amount of acid you take in. You can lower the amount of acid you eat (and therefore the amount of acid your kidneys have to get rid of) by eating less animal protein. Protein is what muscle is made of, and includes fish, beef, chicken and pork. These products also contain some cystine, so limiting your intake of these has 2 benefits.
You can also take in more base to alkalinize your urine. If you eat more fruits and vegetables when you reduce your protein intake, you will take in more base. Base comes in the form of molecules called “organic anions”, such as citrate and malate. They are converted to bicarbonate by the liver. Bicarbonate is the blood’s form of base. One citrate is converted to 3 bicarbonates. So taking citrate and bicarbonate are equivalent. Some of the citrate also is found in the urine where it helps prevent calcium stone formation in non-cystinuric people with the more commonly found calcium oxalate stones. Citrus fruits like oranges and lemons and all fruits and vegetables contain these organic anions.
For most people adequate alkalization does not occur without taking in extra base. It comes in many preparations. Potassium (K) citrate is preferable to sodium citrate preparations because sodium may increase cystine excretion. This is also why I don’t usually prescribe baking soda, which is sodium bicarbonate. But the alkalinizing effect, if it works, could override the increase in cystine excretion. If you are doing well with sodium preparations I would not change your prescription.
The major reason why I sometimes prescribe sodium citrate instead of potassium citrate is if there’s too much potassium in the blood, which is rarely a problem in young people with normal overall levels of kidney function. Another reason to use sodium citrate is taste. Some people prefer it. A third reason is gastrointestinal tolerance. Some people find that potassium citrate causes heartburn, or diarrhea, or abdominal cramps. These are not usually serious side effects but can be avoided by changing preparations.
Sodium bicarbonate comes as baking soda and in pill form. Sodium citrate can be taken as Bicitra, Shoal’s solution. Polycitra (NOT the same thing as Polycitra-K!) has both sodium citrate and potassium citrate in it. All three contain sodium citrate and citric acid. Why is it OK to take citric acid if you are trying to avoid acid? Because the citric acid provides both base (citrate) AND acid, which neutralize each other. It has no net effect on urine pH, unlike the citrate in food which has only the base part, not the proton (H+) part. Why is it there then? To help dissolve the sodium citrate.
Potassium citrate comes in various preparations. Polycitra-K comes as a liquid and in crystals (packets) that you mix in water. It comes in several flavors which are worth trying. In either case they can be sufficiently diluted or mixed into other juices to minimize the taste. Another option is K-Lyte which comes as an effervescent tablet that dissolves in water, like an Alka-Seltzer. It also comes in different flavors worth trying on your kids. It’s a combination of potassium citrate and potassium bicarbonate; that’s OK because citrate and bicarbonate are equivalent. It also comes as “DS” or double strength. (You DON’T want K-Lyte/Cl which is potassium chloride and has no alkalinizing property). Another popular form of potassium citrate is Urocit-K, a pill form. They are actually in a wax matrix from which the drug dissolves. People often see the unabsorbed, undissolved wax in their bowel movements; this does not mean the mineral is not being absorbed.
Compare doses of these preparations in milliequivalents (mEq) of bicarbonate equivalents; ignore the number of milligrams. Most people need anywhere from 20 to 120 mEq per day, but measuring the urine pH is the way to determine how much you need. Bicitra and Shohl’s solution are 15 mEq per tablespoon (1 tbsp=15 cc, cubic centimeters), or 1 mEq per cc. Polycitra liquid has 2 mEq per cc (half as sodium, half as potassium). Polycitra-K liquid is 2 mEq per cc, all potassium. Polycitra-K crystals come as 30 mEq per packet. Urocit-K comes in 5 and 10 mEq tablets. K-Lyte comes as 25 mEq per tab, and 50 mEq for the “double-strength” DS. The standard generic sodium bicarbonate tab (325 milligrams, like an adult aspirin) is about 4 mEq.
I know that people often hesitate when a doctor reaches for a prescription pad. I tell my patients that potassium citrate is more like a vitamin, not a drug. Potassium and citrate are in all of your cells, and all the fruits and vegetables you eat. Both are normally found in urine in significant amounts because we take in more than we need. You can’t be allergic to these minerals, though rarely people are allergic to dyes in the preparations. If your blood potassium is in the normal range you should not have a problem: the extra potassium is excreted by the kidneys. The occasional heartburn or other GI symptoms can usually be overcome by taking them with meals, which doesn’t diminish their absorption or effect on the urine. Sodium citrate or bicarbonate may be a problem for people with decreased heart function, kidney function, or high blood pressure, and can increase urinary cystine levels, but like eating salty pretzels should not cause problems for most otherwise healthy people. I wouldn’t be concerned about taking these “supplements” or about giving them to children. I view these medications as safe and effective, though inexplicably expensive.