As a nephrology pharmacy specialist, you will get questions about how to prevent kidney stones. Calcium stones especially calcium oxalate stones, account for about 80% of kidney stones. And about 50% of patients with a first kidney stone will have another within 5 years without any treatment.
NUTRITIONAL AND DIETARY THERAPIES
Emphasize dietary changes first. Suggest aiming for twelve 8-oz glasses of liquid/day or enough to produce ≥ 2 L/day of urine. Patients with cystine stones may need to drink 4 L of fluid daily to adequately dilute urinary cystine. Increase fluid intake when needed to replace fluid loss through sweat (e.g., in hot weather). Also consider sugar-free real lemonade, a natural citrate source. Epidemiologic data suggest sugar may increase stone risk. Advise limiting soft drinks, especially colas. Colas contain phosphoric acid, which may increase the risk of stones.
- Recommend getting 1000 to 1200 mg/day of calcium from food or from supplements taken with food. Calcium helps bind oxalate in the gut and decreases the amount that gets into the urine, so consume calcium with meals.
- Encourage limiting high-oxalate foods (black tea, chocolate, etc). Many oxalate-containing foods are healthy foods (e.g., spinach, nuts), so moderation, or eating oxalate-containing foods at the same time as calcium-containing foods (so calcium can bind oxalate in the gut), rather than complete avoidance, may be the best option. A list is available from KIDNEY STONE DIET at https://kidneystonediet.com/oxalate-list/. Low oxalate cookbooks are available (e.g., The Low Oxalate Cookbook, Book 2) at http://thevpfoundation.org/vpfcookbook.htm.
- Limit meat, cheese, and eggs. Meats, cheese, and eggs make urine acidic. Meat is a source of purines, which are converted to uric acid. Increase fruits and vegetables, fruits and vegetables provide citrate and make urine more alkaline.
- Limit sodium to 2300 mg (100 mEq) daily. Lower dietary sodium is associated with lower urinary calcium and cystine excretion. 2300 mg of sodium is about one teaspoonful of table salt. Due to larger crystal size, kosher and sea salt may have less sodium per teaspoon (i.e., fewer crystals fit into the spoon).
- Avoid high-dose vitamin C (Vitacid) supplements. Vitamin C (Vitacid) may cause urate, oxalate, or cystine stones. Hyperoxaluria, hyperuricosuria, hematuria, and crystalluria have occurred in people taking 1000 mg or more per day. In people with a history of oxalate kidney stones, supplemental vitamin C 1000 mg per day appears to increase stone risk by 40%.
MEDICATION THERAPY
Add potassium citrate (Citra-Forte, Uralyt U) or a thiazide (Hydretic, Hydrex, HCT georetic) if diet isn't enough especially for patients with recurrent calcium stones. Potassium citrate (Uralyt U) increases urinary pH (goal urine pH is 6 for uric acid stones, and 7 for cystine stones) to help prevent calcium from forming crystals. See table 1 about "Recommendations for the management of kidney stones based on stone type and urine properties".
Thiazides (Hydretic) help reduce calcium excretion. Expect about one in 3 patients to have fewer stones with either med. Use a thiazide if a patient also has hypertension or bone loss and potassium citrate (Uralyt U) for others. Daily doses studied include hydrochlorothiazide 50 mg, chlorthalidone (Hydroton) 25 to 50 mg, and indapamide (Natrilix) 2.5 mg. Lower doses may have fewer side effects, but no proof they work. Save allopurinol (Zyloric, No-Uric) 200 to 300 mg once daily or divided for patients with gout or hyperuricosuria. One in 5 patients will have fewer calcium stones on allopurinol.
| Table (1). Recommendations for the Management of Kidney Stones Based on Stone Type and Urine Properties | ||||
|---|---|---|---|---|
| STONE TYPE | DIAGNOSTIC EVALUATION | INTERVENTIONS | RECOMMENDATIONS | COMMENTS |
| All types | Urine specific gravity > 1.015 | Fluid intake (mostly water) | Drink at least 2 L of water per 24 hours Consider mineral waters, depending on the type of stone |
Mineral content of thousands of mineral waters listed at http://www.mineralwaters.org |
| Body mass index > 25 kg per m² | Weight loss | Promote a healthy diet and exercise | — | |
| Fasting serum glucose level > 105 mg per dL (5.83 mmol per L), random level > 140 mg per dL (7.77 mmol per L) | Suggestive of insulin resistance or early diabetes mellitus | Promote low-glycemic diet (normal range is laboratory-dependent) | ||
| Serum calcium level > 10 mg per dL (2.50 mmol per L) | Consider primary hyperparathyroidism: check intact parathyroid hormone level | |||
| Urine pH (dipstick or from 24-hour urine) | Alkalinize urine (i.e., increase urine pH to 6.5 to 7) with dietary changes or oral supplementation, or until 24-hour urine citrate levels are in the normal range | Alkalinize Potassium citrate: 10 to 20 mEq orally with meals (prescription required) Calcium citrate: two 500-mg tablets per day with meals (each tablet contains 120 mg of calcium and 6 mEq of bicarbonate) |
— | |
| Acidify urine (i.e., lower urine pH to 7 or less) with dietary changes or oral supplementation | Acidify Cranberry juice: at least 16 oz per day Betaine: 650 mg orally three times per day with meals |
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| Calcium oxalate | Stone analysis, if possible | Appropriate protein intake (< 30 percent of total caloric intake) | Take at least 250 mg per dose, or total calcium > 850 mg per day with meals Thiazide diuretics (e.g., hydrochlorothiazide): 25 to 50 mg per day |
Vitamin D increases intestinal calcium absorption, and renal calcium and phosphate absorption |
| Calcium supplements (calcium citrate is preferred if also trying to raise urine citrate levels) | ||||
| Check serum 25-hydroxyvitamin D levels (low limit < 30 ng per mL [74.88 nmol per L]) | ||||
| Thiazide diuretics | ||||
| 24-hour urine oxalate: upper level > 40 mg per day | Diet with moderate amount of fruits and vegetables (do not restrict calcium) | Restrict high oxalate foods (more than 6 mg per serving), such as beans, spinach, rhubarb, chocolate, wheat, nuts, and berries Magnesium potassium citrate: two tablets three times per day with meals (each tablet contains 3 mEq of magnesium, 7 mEq of potassium, and 10 mEq of citrate) Limit vitamin C to less than 1 g per day |
Oxalate restriction is minimally effective and applies primarily to those with genetic mutations in the oxalate transporters | |
| Consider magnesium potassium citrate supplementation | ||||
| Encourage moderate vitamin C intake by dietary sources rather than supplements | ||||
| 24-hour urine calcium (mg calcium per g creatinine): upper level is > 210 in adult men, and > 275 in adult women | Sodium restriction of 2 g per day or less | Avoid foods high in salt (e.g., canned or processed foods, cheese, pickles, dried meats), and do not add salt to food |
— | |
| Do not restrict calcium intake below recommendations for age and sex | ||||
| 24-hour urine magnesium: lower level < 70 mg per day | Increase dietary sources of magnesium | Eat fish, nuts, grains, yogurt Magnesium potassium citrate: two tablets three times per day with meals(each tablet contains 3 mEq of magnesium, 7 mEq of potassium, and 10 mEq of citrate) |
— | |
| Consider magnesium potassium citrate supplementation | ||||
| 24-hour urine citrate: lower level < 450 mg per day in adult men and < 550 mg per day in adult women | Citrate supplementation (available as a potassium, calcium, or sodium salt) | Potassium citrate 10 to 20 mEq orally with meals (prescription required) Calcium citrate: two 500-mg tablets per day with meals |
Sodium salts can increase urinary calcium excretion | |
| Add lemon or lime juice in water | ||||
| 24-hour urine phytates: lower level < 3.8 mg per L of inorganic phosphate, < 0.4 mg per L of inositol phosphate-6 | Consider increased fiber intake | Mix one cup concentrated lemon or lime juice per seven cups water Eat whole grains, legumes, seeds, nuts |
Phytate levels depend on methodology used; increasing phytates may also increase oxalate resorption | |
| Calcium phosphate | Stone analysis | Perform a pregnancy test in women (the risk of calcium phosphate stones is increased with pregnancy) | See Urine pH Decrease intake of dairy products, legumes, chocolate, and nuts by about one-third |
Minimal human data; acidifying urine decreases the formation of calcium phosphate stones in genetically predisposed rats |
| Acidify urine | ||||
| Consider decreasing dietary phosphate intake | ||||
| Uric acid | Urine pH < 5.5 | Increase urine pH to > 6 | Increase fluid intake | Alkalinization increases solubility of uric acid |
| Alkalinize urine | ||||
| Consider alkalinizing agents | ||||
| Cystine | Stone analysis | Increase fluid intake to maintain urine volume > 3 L per day | Fluids: Alkalinize urine and maintain a urine volume > 3 L per day | Low urine volume is the strongest risk factor for cystine stone formation |
| Alkalinize urine | ||||
| Consider alkalinizing agents | ||||
REFERENCES
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Fink HA, Wilt TJ, Eidman KE, Garimella PS, MacDonald R, Rutks IR, Brasure M, Kane RL, Ouellette J, Monga M. Medical management to prevent recurrent nephrolithiasis in adults: a systematic review for an American College of Physicians Clinical Guideline. Ann Intern Med. 2013 Apr 2;158(7):535-43. Available at: https://www.acpjournals.org/doi/10.7326/0003-4819-158-7-201304020-00005
National Kidney Foundation. Diet and kidney stones. Available at: https://www.kidney.org/atoz/content/diet
Shuster J, Jenkins A, Logan C, Barnett T, Riehle R, Zackson D, Wolfe H, Dale R, Daley M, Malik I, et al. Soft drink consumption and urinary stone recurrence: a randomized prevention trial. J Clin Epidemiol. 1992 Aug;45(8):911-6. Available at: https://pubmed.ncbi.nlm.nih.gov/1624973
Pearle MS, Goldfarb DS, Assimos DG, Curhan G, Denu-Ciocca CJ, Matlaga BR, Monga M, Penniston KL, Preminger GM, Turk TM, White JR; American Urological Assocation. Medical management of kidney stones: AUA guideline. J Urol. 2014 Aug;192(2):316-24. Available at: https://www.auajournals.org/doi/10.1016/j.juro.2014.05.006
Frassetto L, Kohlstadt I. Treatment and prevention of kidney stones: an update. Am Fam Physician. 2011 Dec 1;84(11):1234-42. Available at: https://www.aafp.org/pubs/afp/issues/2011/1201/p1234.html