A novel sustained-release cysteamine bitartrate formulation for the treatment of cystinosis: pharmacokinetics and safety in healthy male volunteers

The strict intake regimen of cysteamine bitartrate formulations, associated with side effects, is a concern for the treatment compliance in cystinosis therapy. Therefore, there is a need for a cysteamine formulation with an improved pharmacokinetic profile. This study investigated the pharmacokinetics, safety and tolerability of a new sustained-release cysteamine dosage form, PO-001, in healthy volunteers. This was a randomized, investigator-blinded, three-way cross-over study to compare single doses (600 mg) of PO-001 with Cystagon® (immediate-release) and Procysbi® (delayed-release). Collected blood samples were analyzed for plasma cysteamine concentrations and pharmacokinetic parameters were estimated by noncompartmental analysis. In addition, plasma cysteamine concentrations were analyzed using a population pharmacokinetic approach using NONMEM®. Pharmacokinetics showed clear sustained-release characteristics of PO-001 over time with a lower Cmax and longer Tmax compared to Cystagon® and Procysbi®. All treatment-emergent adverse events were of mild severity, with the exception of two subjects who reported moderate severity gastrointestinal problems including vomiting and diarrhea, which were related to Cystagon® intake. Population PK simulations showed a favourable PK profile based on Cmax and Ctrough concentrations at steady state. In conclusion, a single dose of 600 mg PO-001 was well tolerated with no findings of clinical concern. This new cysteamine bitartrate formulation showed pharmacokinetics of a sustained-release formulation, which may be beneficial for the treatment of cystinosis patients. This study supports advancing this type of sustained-release formulation into a subsequent study to confirm reduced dosing frequency with efficient control of white blood cells (WBCs) cystine levels. Netherlands Trial Registry (NTR) (NL67638.056.18).