Are pleuromutilin antibiotics finally fit for human use?

In 1951, the first reference to the antibacterial substance pleuromutilin was made in a paper published in the Proceedings of the National Academy of Sciences. Researchers had identified several species of the mold genus Pleurotus that inhibited the growth of Staphylococcus aureus. The elucidation of the structure in 1962 led to the initiation of a development program at Sandoz, which was followed by the approval of tiamulin in 1979 for use in veterinary medicine. Although in 2007 retapamulin became the first pleuromutilin approved for topical use in humans, it was not until 2011, exactly 60 years after the first mention of the class, that a pleuromutilin antibiotic, BC-3781, could be tested successfully in a clinical phase II trial for systemic use in patients. This review will discuss key aspects of this antibacterial class and provide some insight into the question of why it took half a century to develop a systemic pleuromutilin for human use.