The new Pfizer drug, with 89% efficacy, is a protease inhibitor targeting 3CLPro. Ivermectin seems to also work as a protease inhibitor targeting 3CLPro. Repurposing a drug that we know is safe means it came be deployed very rapidly. New and unknown drugs can take years before all side effects are known.
If anyone is interested in hearing an informed opinion on Ivermectin check out Dr. John Campbell: https://www.youtube.com/watch?v=ufy2AweXRkc