The protective effect of some phenothiazine derivatives against streptolysin O

1 Chlorpromazine (Cpz) and promethazine (Pmz) protected mice against lethal doses of streptolysin O (SLO) given intravenously. Three other phenothiazine derivatives had similar but lesser effects. 2 The protective effect developed slowly; maximal protection was obtained 4 h after subcutaneous injection of Cpz and Pmz. 3 The haemolytic activity of SLO in vitro was also inhibited by Cpz.