The present invention provides a novel process for preparing pleuromutilin derivatives, novel salts of mutilin 14-(exo-8-methyl-8-azabicyclo[3.2.1]oct-3-ylsulfanyl)-acetate or solvates thereof, novel pharmaceutical compositions or formulations for topical administration comprising mutilin 14-(exo-8-methyl-8-azabicyclo[3.2.1]oct-3-ylsulfanyl)-acetate or a pharmaceutically acceptable salt or solvate thereof and their use in medical therapy, particularly antibacterial therapy.