Cystinosis is an inherited disease that if untreated, results in kidney failure as early as the first decade of life. The current marketed therapy is Cystagon® (cysteamine bitartrate immediate release) which must be taken every six hours for the rest of the patient's life to prevent complications of cystinosis. Cysteamine bitartrate delayed-release capsules (RP103) is a formulation of cysteamine bitartrate that is being studied to see if it can be given less frequently, once every 12 hours, and have similar results to four times a day Cystagon®.

This is a long-term, open-label, study to determine the safety and tolerability of twice a day treatment with cysteamine bitartrate delayed-release capsules (RP103). It will involve 6-9 monthly clinic visits followed by quarterly clinic visits for the duration of the study and home use of cysteamine bitartrate delayed-release capsules.

Initially, enrollment was open to those patients who had completed the previous Phase 3 Study (RP103-03, NCT01000961). Subsequently enrollment in Study RP103-04 was opened to additional participants, including children aged 1 to 6 years and renal transplant recipients, who had previously been on a stable dose of Cystagon® for at least 21 days.

Study with completed results acquired from Horizon in 2024.

Inclusion Criteria:

• Male and female subjects must have completed the last visit of Study RP103-03 and be willing to continue with RP103 treatment.

OR for patients who did not complete the RP103-03 study:

• Male and female subjects must have cystinosis.
• Subjects must be on a stable dose of Cystagon® at least 21 days prior to Screening.
• Within the last 6 months, no clinically significant change from normal in liver function tests (i.e., alanine aminotransferase [ALT], aspartate aminotransferase [AST], total bilirubin) and renal function (i.e., estimated glomerular filtration rate [eGFR]) at Screening as determined by the Investigator.
• Subjects with an eGFR corrected for body surface area > 30 mL/min/1.73m².
• Sexually active female subjects of childbearing potential (i.e., not surgically sterile [tubal ligation, hysterectomy, or bilateral oophorectomy] or at least 2 years naturally postmenopausal) must agree to utilize the same acceptable form of contraception from Screening through completion of the study.
• Subjects must be willing and able to comply with the study restrictions and requirements.
• Subjects or their parent or guardian must provide written informed consent and assent (where applicable) prior to participation in the study.

Exclusion Criteria:

• Patients enrolled in the previous Study RP103-03 who did not complete their last scheduled Study visit or who do not wish to continue on treatment with RP103.

AND for patients who did not complete the RP103-03 study:

• Subjects less than 1 year old
• Subjects with a known history, currently of the following conditions or other health issues that make it, in the opinion of the investigator, unsafe for them to participate: inflammatory bowel disease (if currently active) or have had prior resection of small intestine; Heart disease (e.g., myocardial infarction, heart failure, unstable arrhythmias or poorly controlled hypertension) 90 days prior to Screening; Active bleeding disorder 90 days prior to Screening; Malignant disease within the last 2 years.
• Patients with a hemoglobin level < 10 g/dL at Screening or a level that, in the opinion of the investigator, makes it unsafe for the subject to participate.
• Subjects with known hypersensitivity to cysteamine or penicillamine.
• Female subjects who are nursing, planning a pregnancy, known or suspected to be pregnant, or have a positive serum pregnancy screen.
• Subjects who, in the opinion of the Investigator, are not able or willing to comply with the protocol.

Safety population

From first dose of study drug to 7 days after last dose; median duration of treatment was 1461 days.