Cysteamine

Cystagon is indicated for the treatment of nephropathic cystinosis, a rare autosomal recessive lysosomal storage disorder. In patients with this condition, the defective CTNS gene results in impaired cystine transport, leading to crystal formation in various tissues including the kidneys, eyes, muscles, and nervous system. Early treatment helps prevent or delay organ damage and deterioration.

Cysteamine, the active ingredient in Cystagon, penetrates cells and reacts with cystine within lysosomes. It converts cystine into cysteine and a cysteine-cysteamine mixed disulfide compound that can be transported out of the lysosome via a separate transporter system. By depleting intracellular cystine levels, the medication prevents the formation of toxic cystine crystals that cause cellular damage and organ dysfunction.

Cystagon must be taken consistently every 6 hours around the clock for life to maintain cystine depletion. Common side effects include gastrointestinal symptoms (nausea, vomiting, anorexia, diarrhea), lethargy, and body odor or bad breath due to sulfur-containing metabolites. The medication should be taken with food or milk to reduce GI upset. Dose titration is typically required to minimize side effects while achieving therapeutic efficacy. Close monitoring of white blood cell cystine levels is important to ensure adequate dosing.