What are special considerations in the drug therapy of nephrolithiasis?
Potassium citrate, and not sodium citrate, for urine alkalinization to a pH > 7.0 is recommended for uric acid and cystine stones. Sodium citrate increases urinary sodium and calcium, and in alkaline urine, sodium urate may increase calcium stone formation. Cystine stone formers require higher fluid intake to reduce urinary cystine below its solubility limit of 200 to 250 mg/L and produce a urine output of 3 L/day. The cystine-binding thiol drugs tiopronin and penicillamine help reduce urinary cystine. Tiopronin has fewer side effects and should be tried first. Dietary purine and fructose restriction, adequate fluid intake, and potassium citrate often are the only therapy necessary for uric acid stones if uricosuria is < 800 mg/day. Use the xanthine oxidase inhibitor allopurinol with potassium citrate if uric acid stones continue or hyperuricemia is more severe. Use cellulose sodium phosphate (CSP) only for refractory stone disease in AH-I. CSP binds calcium and magnesium in the gut, decreases absorption of both, and may worsen osteopenia and increase urinary oxalate. Replace magnesium, as required. Monitor bone mass and treat osteopenia, as necessary.
