Disclosed are antibiotic 6-[1-hydroxyethyl]-2-SR.sup.8 -1-methyl-1-carbadethiapen-2-em-3-carboxylic acids and their pharmaceutically acceptable salts and esters (I): ##STR1## wherein: R.sup.8 is ##STR2## and ##STR3## wherein: R.sup.8 is ##STR4## and wherein n and m are independently selected from 0, 1, 2, 3, 4 and 5; X is --NR; and Y is --R, or --NRR; and wherein R is independently selected from hydrogen, alkyl, alkenyl, alkynyl, (having 1-6 carbon atoms); cycloalkyl and cycloalkenyl (having 3-6 carbon atoms); and heterocyclyl, heteroaryl (having 3-6 ring atoms, one or more of which is N, O or S).