WELL Duquesne University Mylan School of Pharmacy
UPDATE from the Center for Pharmacy Care
The Hard Facts About
idney stones, sometimes called renal calculi, are responsible for approximately 2.7 million physician ofﬁce visits each year and nearly 600,000 trips to hospital emergency departments. The condition, referred to as nephrolithiasis or urolithiasis, has existed for millennia and the presence of kidney stones has been described in a 7,000 year-old Egyptian mummy. Kidney stones are masses of crystals that have formed on the inner surfaces of the kidney. They may be as small as grains of salt or as large as golf balls (or larger!). Tiny stones may pass through the kidneys and ureters (tubes connecting the kidney to the bladder; see Figure 1) without producing symptoms. Larger stones can cause severe pain and other complications. Substances such as citrate and magnesium normally prevent crystal formation and the development of stones. Reduced levels of these chemicals as well as several other factors predispose patients to kidney stones. These factors include a family history of kidney stones, frequent urinary tract
Kidney Stone Path
Kidney stones sometimes pass into one of the two tubes (ureters) leading from your kidneys to your bladder. Mayo Clinic. Kidney Stones. www.mayoclinic.com/popupnowrap.cfm?objectid= 0B8CA25D-C103-4F64-BE9F088CFDCCA592&me thod=display_full (accessed 19 March 2007)
infections, rapid changes in acid content of the urine, various kidney disorders, excess activity of the parathyroid gland, metabolic disorders
such as cystinuria, etc. In general, kidney stones will reappear on multiple occasions. They occur more frequently in men than women and their prevalence has increased since the 1970s. The frequency of kidney stones increases as men progress from age 40-70. In women, stone formation occurs most often in the 50s. The most common initial symptom of a kidney stone is sudden onset of extreme pain in the lower back and side or in the lower abdomen. This sharp pain may ﬂuctuate in intensity over periods of 5-15 minutes and can radiate to the groin and other areas. Pain occurs because the stone blocks the ﬂow of urine and also irritates the muscles of the ureter as it attempts to move the stone into the bladder. Nausea and vomiting can accompany passage of the stone and blood may be observed in the urine. Blood and urine tests may be required to identify the cause and type of kidney stone. Ultrasound studies, a computed tomography (CT) scan, or intravenous pyelogram (IVP) may be required to determine the size and location of the stone.
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The Hard Facts About Kidney Stones Types and Treatments of Kidney Stones Kidney stones are categorized by their chemical content. Each of the four major types has a speciﬁc cause and recommended treatment (s). • Calcium stones: These are the most common form and account for approximately 90% of renal calculi. They usually appear to be caused by increased urinary calcium levels (also called hypercalciuria). In most patients, the cause of hypercalciuria is unknown. Calcium is absorbed from food and the excess is excreted in the urine where it combines with oxalate or phosphate and crystallizes. Oxalate occurs naturally in some fruits and vegetables like rhubarb, spinach, beets, strawberries, and wheat bran. Large amounts of vitamin D, some medications, calcium-based antacids, some types of cancer, and an overactive parathyroid gland may increase urine calcium concentrations. Intestinal bypass surgery and a diet high in oxalic acid can also increase the risk of calcium stones. Diuretics such as hydrochlorothiazide can reduce the amount of urinary calcium. A prescription drug known as sodium cellulose phosphate binds to calcium in the intestine and may be used to decrease the amount reaching the blood and urine. • Struvite stones: These stones occur more often in women than men and are almost always associated with chronic urinary tract infection. Responsible bacteria produce speciﬁc enzymes that increase urine levels of ammonia. The excess ammonia combines with magnesium and phosphate resulting in struvite (the chemical name for ammonium, magnesium, and phosphate) stone formation. The stones tend to be large and often have a characteristic stag-horn shape. These types of stones generally remain in the kidney because they are too large to enter the ureters. • Uric acid stones: These are less common than struvite stones and are formed as a by-product of protein breakdown. They can be caused by high protein diets and rare genetic disorders. Patients with gout may also develop uric acid stones. Chemotherapy for various forms of leukemia and lymphoma may also result in this type of stone. The
physician may recommend drugs that alkalinize the urine, an important factor for preventing uric acid calculi. Patients with increased blood levels of uric acid may be prescribed allopurinol (Zyloprim). • Cystine stones: These stones are rare and appear to occur in patients with a hereditary disorder (cystinuria) that causes the kidneys to excrete excessive quantities of an amino acid known as cystine. Drugs like Thiola and Cuprimine may reduce the amount of cystine in the urine. Surgery or other procedures may be necessary if the stone does not pass in a reasonable period of time and continues to cause signiﬁcant pain. Other indications for surgery include blockage of urine ﬂow, chronic urinary tract infection, frequent bleeding, or the presence of a stone that is too large to pass on its own. There are few options and the type of procedure will be dependent on the site and size of the renal stone. Extracorporeal Shockwave Lithotripsy (ESWL) is the most common method currently in use. In this procedure, shock waves are created by a device outside the body that break the stone into smaller particles that eventually pass naturally through the urinary tract. ESWL normally requires anesthesia, but can be accomplished on an outpatient basis. Complications include blood in the urine, bruising, and discomfort when the stone particles pass through the urinary tract. Another method is called Percutaneous Nephrolithotomy (PNL or PCNL). This is commonly used if the stone is large or located where ESWL may be ineffective. In this procedure, the surgeon makes a small incision in
Newsletter Contributors John G. Lech, Pharm.D. Joshua J. Willey, Pharm.D. Candidate
For additional information on kidney stones, please visit the following Web sites: • • • •
www.kidney.org kidney.niddk.nih.gov/kudiseases/pubs/stonesadults/ www.mayoclinic.com/health/kidney-stones/DS00282 www.nlm.nih.gov/medlineplus/kidneystones.html
the back and, using a nephroscope, locates and removes the stone. PNL may require a few days of hospitalization. Lastly, Ureteroscopy is used for stones located in the mid- to lower-ureter. The surgeon places a small ﬁberoptic instrument called an ureteroscope through the urethra and bladder into the ureter. The stone is removed with a cage-like device after which a stent is placed in the ureter to assist in healing.
Prevention There are some things you can do to assist the physician in managing this condition and preventing the formation of future stones. It will be necessary for the physician to identify the type of kidney stone you have and the reason it developed. The doctor will order laboratory tests and may ask you to collect urine samples in order that they can be analyzed for levels of acidity and concentrations of calcium, sodium, uric acid, oxalate, citrate, etc. The single most important thing you can do to prevent development of new stones is to drink plenty of liquids, preferably water. It is usually recommended that patients drink enough liquid to pass at least 2-2.5 quarts of urine a day. In order to do so, you would have to consume about 3.5 quarts (14 cups) every day. Reducing your use of foods high in oxalic acid and lowering your intake of sodium may also lessen your risk of developing calcium stones. People who form calcium stones were previously told to avoid foods containing calcium; however, recent studies suggest that increased calcium intake may actually reduce the risk of this type of stone. Kidney stones can be a very painful experience. By following your doctor’s instructions, you might be fortunate that they only occur once.
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