Open-Label, Safety and Superior Effectiveness Study of Cysteamine Bitartrate Delayed-Release Capsules (RP103) in Cystinosis

The purpose of this study is to gather information about the effectiveness (how well it works to treat cystinosis) and safety of a new form of cysteamine bitartrate called RP103, compared to the already-approved drug cystinosis patients are taking called Cystagon®.

In cystinosis, the body builds up cystine. When taken regularly, the active ingredient of Cystagon® (cysteamine bitartrate) reduces cystine in the body. RP103 has the same active ingredient as Cystagon® and is designed to reduce cystine in a similar way that Cystagon® does. To decide if RP103 is better than Cystagon®, the study will look at two types of blood tests. One test is pharmacodynamics (PD), which measures the amount of white blood cell (WBC) cystine after taking study drug. WBC cystine is a laboratory test used to find out if cysteamine bitartrate is reducing cystine levels in the body. The second test is pharmacokinetics (PK), which measures the amount of cysteamine in the blood after taking the drug.

RP103 is different from Cystagon®: Instead of the cysteamine bitartrate being absorbed from the stomach, RP103 is designed to be absorbed from the small intestine. This may make the effects of the drug last longer, so that it can be taken twice a day instead of four times a day like Cystagon®.

Some cystinosis patients have bad breath (halitosis) when they take Cystagon®. Study participants who experience bad breath with Cystagon® will be asked if they would like to participate in an optional "halitosis substudy" to investigate this issue by collecting some extra PK blood samples.

Study with completed results acquired from Horizon in 2024.

Eligibility Criteria:
INCLUSION CRITERIA:

* Male or female with a documented diagnosis of cystinosis
* On a stable dose of Cystagon® at least 21 days prior to Screening
* WBC cystine level \> 1 nmol 1/2 cystine/mg of protein, on average over at least 2 measurements collected during the 2 years prior to Screening
* No clinically significant change in liver function tests, i.e. 1.5 times upper limit of normal (ULN) for alanine aminotransferase and aspartate aminotransferase, and/or 1.5 times ULN for total bilirubin, within 6 months prior to Screening
* No clinically significant change in renal function, i.e. estimated glomerular filtration rate (GFR) within 6 months prior to Screening
* Must have an estimated GFR \> 20 mL/minute/1.73m\^2 (using the equation from Schwartz 2009 J Am Soc Nephrol 20:629-647)
* Female subjects who are sexually active and of childbearing potential, i.e. not surgically sterile (tubal ligation, bilateral oophorectomy, or hysterectomy) or at least 2 years naturally postmenopausal must agree to use an acceptable form of contraception from Screening through completion of the study. Acceptable forms of contraception for this study include hormonal contraceptives (oral, implant, transdermal patch, or injection) at a stable dose for at least 3 months prior to Screening, barrier (spermicidal condom or diaphragm with spermicide), intrauterine device, or a partner who has been vasectomized for at least 6 months.
* Subject or their parent or guardian must provide written informed consent, assent (where applicable), prior to participation in the study

EXCLUSION CRITERIA:

* Younger than 12 years of age
* Current history of the following conditions or any other health issues that make it, in the opinion of the investigator, unsafe for study participation:

  * Inflammatory bowel disease, if currently active, or prior resection of the small intestine;
  * Heart disease (e.g., myocardial infarction, heart failure, unstable arrhythmias, or poorly controlled hypertension) within 90 days prior to Screening;
  * Active bleeding disorder within 90 days prior to Screening;
  * History of malignant disease within 2 years prior to Screening
* Hemoglobin level of \< 9 g/dL at Screening or, in the opinion of the investigator, a hemoglobin level that would make it unsafe for study participation
* Known hypersensitivity to cysteamine and penicillamine
* Female subjects who are nursing, planning a pregnancy, or are known or suspected to be pregnant
* Subjects who, in the opinion of the investigator, are not able or willing to comply with study requirements.