Disclosed is the antibiotic 6-(1-hydroxyethyl)-2-substituted-thio-3-tetrazolyl-1-carbadethiapen-2-em and its pharmaceutically acceptable salts (I): ##STR1## wherein Z is C.sub.1 -C.sub.3 alkylamino, C.sub.1 -C.sub.3 alkylguanidino, C.sub.1 -C.sub.3 alkylamidino, or heterocycloalkyl and, M=H, a synthetically useful cation, or pharmaceutically acceptable cation. Such compounds as well as their pharmaceutically acceptable salts are useful as antibiotics. Also disclosed are processes for the preparation of such compounds; novel intermediates; pharmaceutical compositions comprising such compounds; and methods of treatment comprising administering such compounds and compositions when an antibiotic effect is indicated.