#1593 Cystine-binding drugs are poorly available for the treatment of cystinuria

Abstract Background and Aims Cystinuria is an autosomal recessive disease characterized by defective transepithelial transport of cystine, lysine, arginine, and ornithine in the renal proximal tubule. The high urine cystine concentrations put cystinuria patients at great risk for the development of cystine stones. The treatment consists of lifestyle advices, hyperhydration and alkalizing supplements, whereas in refractory cases cystine-binding drugs, such as tiopronin or D-penicillamine, are used to lower the risk for renal stone disease and subsequent chronic kidney disease. Because of limited number of manufacturers and high costs, the availability of cystine-binding drugs is highly variable. Method An online questionnaire was distributed to members of the European Reference Network for Rare Kidney Diseases (ERKNet) on behalf of the Metabolic Nephropathy Workgroup to assess the availability of cystine-binding drugs for patients with cystinuria. Additional questions about the local availability of tiopronin and/or D-penicillamine were asked when physicians prescribed these drugs in the last two years. We excluded participants who completed less than 95% of the questionnaire. The collected data were analyzed using descriptive statistics. Results We included 40 physicians from 15 countries (Fig. 1A), including pediatric nephrologists (55%), adult nephrologists (40%) and adult urologists (5%). The majority had 5–10 (28%) or 10–20 (35%) years of clinical experience with treating cystinuria patients and had treated a median of 15 [IQR 8–38] patients. The use of cystine-binding drugs in clinical practice varied substantially among physicians (Fig. 1B; median 35% [IQR 20–68]). Tiopronin was the drug of preference for 53% of the physicians, whereas 25% preferred D-penicillamine. Tiopronin was recently prescribed by 57%, but 83% of the prescribing physicians (19/23) experienced problems with access of tiopronin. Sixteen (70%) physicians experienced problems with the availability, in 20% [IQR, 5%–35%] of the prescriptions (Fig. 1C). Restricted access to tiopronin due to policies of insurance companies was reported by 22% of the prescribing physicians. Thirty percent of the physicians had no access to tiopronin at all. D-penicillamine was recently prescribed by 45% of the physicians and 61% of the prescribing physicians experienced problems with the availability of D-penicillamine (Fig. 1C). Conclusion Cystine-binding drugs are currently poorly available for the treatment of cystinuria in Europe. Considering the added value of these drugs for the treatment of cystinuria, the availability should be improved.