Two 40-week extension studies followed people who had already completed shorter rosacea trials, bringing total treatment to about a year. The question was safety rather than efficacy. Ivermectin produced fewer treatment-related side effects than azelaic acid, and nobody stopped ivermectin because of one. Long-term safety data like this is genuinely useful, since most trials run 12 weeks and then stop asking.
Stein Gold L, Kircik L, Fowler J, et al. Long-term safety of ivermectin 1% cream vs azelaic acid 15% gel in treating inflammatory lesions of rosacea: results of two 40-week controlled, investigator-blinded trials. J Drugs Dermatol. 2014;13(11):1380-1386.
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