Adherence to delayed-release cysteamine in nephropathic cystinosis over time: data from the prospective CrYSTobs cohort study.

Background: Adherence to cysteamine in nephropathic cystinosis (NC) remains challenging. A better adherence with delayed-release (DR) compared to immediate-release (IR) cysteamine at 1 year was previously shown. This study aimed to evaluate adherence to DR cysteamine at 2 years.

Methods: Treatment adherence was assessed using a medication event monitoring system; adherence ranged from 0 (poor) to 2 (good). Leukocyte cystine level was measured at each 3-month visit. Long-term follow-up data (7 years after the end of the study) on self-reported adherence and quality of life was also obtained in a sub-group of patients.

Results: Seventeen patients with NC under DR cysteamine from three French centers were included at a median age of 13.9 (5.4-33.0) years. The median adherence score was 1.62 (0.03-1.98) over the 2-year follow-up, with 65% of patients having good adherence and 75% having partial or good adherence. No significant difference in leukocyte cystine level between baseline and 2 years was found (0.8 nmol vs. 0.4 nmol, respectively; difference in median of - 1.0 nmol; 95% CI - 0.7, 0.4; P = 0.64). Long-term follow-up data highlighted that no patient wished to switch back to IR cysteamine, as taking the medication twice rather than four times a day was easier.

Conclusions: This study found a fairly good adherence to DR cysteamine over time. Decreasing the number of intakes per day may improve adherence and limit the side effects of the drug, representing an additional argument in favor of its use in patients with cystinosis.