Medication Summary
The goals of pharmacotherapy are to reduce morbidity and to prevent complications.
Allopurinol has been associated with the development of hemorrhagic skin lesions, exfoliation, and a rare fatal systemic vasculitis. Pruritus often precedes the development of rash and should prompt patients to discontinue the medication. Alterations in hepatic function and jaundice have been reported with allopurinol use; these complications require monitoring of serum liver function test results soon after the institution of therapy. Allopurinol may result in an acute gouty attack in patients with hyperuricemia.
Urinary alkalinizing agents
Class Summary
The most important medications used for the dissolution or prevention of uric acid urinary stones are alkalinizing agents (eg, potassium citrate) to increase the urinary pH to 6.5-7.0. Balanced citrate alkali (eg, potassium citrate; Urocit-K, Polycitra-K) are the most commonly used medications. Sodium and potassium bicarbonate are also used frequently. One disadvantage of sodium alkali is that the increased sodium and fluid load may be detrimental to patients with renal failure, liver failure, or congestive heart failure.
Alternatively, citrate supplementation may be given. Citrate inhibits calcium oxalate crystallization directly and by complexing with calcium in solution to reduce its concentration and availability. Potassium citrate is preferred over sodium citrate because it is not associated with a sodium load. Potassium citrate comes in a slow-release wax-based tablet, which may be seen as an intact tablet in the stool; however, the citrate has been absorbed. Patients should be warned that this may occur.
For patients who are not tolerant of or compliant with a frequent dosing schedule, a single evening dose may be quite beneficial to increase the urinary pH (alkaline tide) overnight.
Potassium citrate can also be given as a crystal preparation. The advantage of this preparation is that it forces patients to increase their fluid intake. Potassium citrate may be given in liquid preparations, with and without glucose additives. Finally, lemonade has been shown to increase urinary citrate levels and is an alternative or supplement to pharmacologic formulations.
The primary treatment for uric acid stones is urinary alkalinization. Surprisingly, it is not associated with hypocitraturia. Allopurinol should be added to the therapeutic regimen in the presence of associated hyperuricemia, hyperuricosuric calcium stone disease, intolerance of alkali, or continuing uric acid stone production despite alkalinization therapy. Initial dosing should be 300 mg/d.
Potassium citrate (Urocit-K, Polycitra-K)
Available as tab, syr, and crystals. All forms should be taken with water or juice according to directions.
Potassium bicarbonate/potassium citrate (Effer-K, K-Ide, Klor-Con/EF, K-Lyte)
Needed for conduction of nerve impulses in heart, brain, and skeletal muscle. Helps maintain normal renal function. Plays role in contraction of cardiac, skeletal, and smooth muscles. All PO forms of potassium bicarbonate should be taken with adequate fluids according to directions.
Sodium bicarbonate (Neut)
Excellent urinary alkalinization agent. Dissociates to provide bicarbonate ion, which neutralizes hydrogen ion concentration and raises blood and urinary pH.
Antihyperuricemic agents
Class Summary
In cases of hyperuricemia or significant hyperuricosuria, allopurinol is effective. This drug inhibits the conversion of hypoxanthine and xanthine to uric acid. In patients with hyperuricosuric calcium stones, treatment involves reducing the monosodium urate–induced calcium oxalate crystallization. This is accomplished by decreasing urinary uric acid excretion and limiting dietary sodium intake (< 150 mEq/d). Patients should initially be treated with dietary purine and sodium restriction. In approximately 30% of patients, hyperuricosuria is due to uric acid overproduction and does not improve with dietary restriction. In this situation and in patients intolerant of diet restriction, allopurinol is the medication of choice.
Allopurinol (Zyloprim)
Inhibits xanthine oxidase, the enzyme that synthesizes uric acid from hypoxanthine. Reduces the synthesis of uric acid without disrupting the biosynthesis of vital purines.
-
CT scan demonstrating right partial staghorn uric acid calculus. Uric acid stones appear dense on CT scan and radiolucent on kidneys, ureters, and bladder (KUB) imaging (not shown).
-
Follow-up CT scan of patient in the image above (ie, with partial staghorn uric acid calculus) 1 year later. This patient was treated with oral urinary alkalinization with sodium bicarbonate. Note only a small residual fragment is present (right image).
