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Mechanism of Action

Cysteamine acts as a cystine-depleting agent by converting cystine to cysteine and cysteine-cysteamine mixed disulfides and reduces corneal cystine crystal accumulation.


The peak plasma concentration of cysteamine following ocular administration of cysteamine ophthalmic solution in humans is unknown, but it is expected to be substantially less than the peak plasma concentration following oral administration of cysteamine bitartrate.

Clinical Studies

Clinical efficacy was evaluated in controlled clinical trials in approximately 300 patients. The primary efficacy end point was the response rate of eyes that had a reduction of at least 1 unit in the photo-rated Corneal Cystine Crystal Score (CCCS) at some time point during the study when baseline CCCS ≥ 1, or a lack of an increase of more than 1 unit in CCCS throughout the study when baseline CCCS < 1.

Study 1 combined the data from three smaller studies. For eyes with a lower baseline of CCCS < 1, the response rate was 13% (4/30) [95% CI: (4, 32)]. For eyes with a higher baseline of CCCS ≥ 1, the response rate was 32% (94/291) [95% CI: (27, 38)].

Study 2 evaluated ocular cystinosis patients who had a baseline of CCCS ≥ 1. The response rate was 67% (10/15) [95% CI: (38, 88)].

Study 3 also evaluated ocular cystinosis patients; for eyes with a baseline of CCCS ≥ 1, the response rate was 33% (3/9) [95% CI: (8, 70)].

Corneal crystals accumulate if CYSTARAN is discontinued.

Last reviewed on RxList: 10/11/2012
This monograph has been modified to include the generic and brand name in many instances.

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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