The effects of transitioning from immediate release to extended release cysteamine therapy in Norwegian patients with nephropathic cystinosis: a retrospective study

BACKGROUND: Nephropathic cystinosis is a rare lysosomal storage disorder in which accumulation of cystine and formation of crystals particularly impair kidney function and gradually lead to multi-organ dysfunction. Lifelong therapy with the aminothiol cysteamine can delay the development of kidney failure and the need for transplant. The purpose of our long-term study was to explore the effects of transitioning from immediate release (IR) to extended release (ER) formulation in Norwegian patients in routine clinical care.

METHODS: We retrospectively analysed data on efficacy and safety in 10 paediatric and adult patients. Data were obtained from up to 6 years before and 6 years after transitioning from IR- to ER-cysteamine.

RESULTS: Mean white blood cell (WBC) cystine levels remained comparable between the different treatment periods (1.19 versus 1.38 nmol hemicystine/mg protein) although most patients under ER-cysteamine underwent dose reductions. For the non-transplanted patients, the mean estimated glomerular filtration rate (eGFR) change/year was more pronounced during ER-treatment (- 3.39 versus - 6.80 ml/min/1.73 m2/year) possibly influenced by individual events, such as tubulointerstitial nephritis and colitis. Growth measured by Z-height score tended to develop positively. Four of seven patients reported improvement of halitosis, one reported unchanged and two reported worsened symptoms. Most adverse drug reactions (ADRs) were of mild severity. One patient developed two serious ADRs and switched back to IR-formulation.

CONCLUSIONS: The results from this long-term retrospective study indicate that switching from IR- to ER-cysteamine was feasible and well tolerated under routine clinical practice. ER-cysteamine allowed satisfactory disease control over the long period considered. A higher resolution version of the Graphical abstract is available as Supplementary information.