Complex sentence: As previously mentioned, the first drug in the SSRI class to be developed and marketed was zimeldine, but unfortunately several cases of Guillain-Barré syndrome were associated with the use of the drug and led to withdrawal from the market in 1983.
Split into simpler sentences: As previously mentioned, the first drug in the SSRI class to be developed, and to be marketed, was zimeldine. Unfortunately several cases of Guillain-Barré syndrome were associated with the use of the drug which led to withdrawal from the market in 1983.