<p><strong>In adult and pediatric patients with recurrent cystine stones despite dietary and alkali therapy, clinicians may offer cystine-binding thiol drugs. (<em>Expert Opinion</em>)</strong></p>
Discussion
Discussion
<p>For patients with recurrent cystine stones, recommended management includes increased fluid intake, restriction of dietary sodium, modest restriction of protein intake in adults, and urinary alkalinization. The goal urinary pH during alkalinization therapy is 7.0-7.5. Cystine-binding thiol drugs may be added in patients who continue to form cystine stones despite these interventions.<sup>219</sup> Tiopronin (alpha-mercaptopropionylglycine) has fewer side effects than d-penicillamine and results in increased solubility of cystine in urine; captopril, on the other hand, is not effective in preventing cystine stone formation.<sup>24, 220</sup> Vitamin B6 supplementation is recommended during penicillamine therapy because of chelation; however, supplementation is not required with tiopronin. Discussion of potential drug-related adverse effects and periodic laboratory monitoring should be performed (as described in <strong>Table 7 and Statement 39</strong>). Cystine capacity, a proprietary assay that assesses cystine stone-forming potential, may be used to monitor the effectiveness of cystine-binding thiol drugs and guide dose titration with the goal of maintaining cystine levels below the solubility threshold of 250 mg/L.<sup>221</sup></p>