The advice I would give is to use Lustrate, because it's an instant use (no cast). I have a macro that is like

/macroicon "Physick"
/macroerror off
/recasterror off
/action "Lustrate"
/action "Physick"

I put it on the hotbar and keybind that hotbar button to Shift+2, then click a person in the party list and Shift+2 them.

I'm not going to say it's never failed, but it almost never does and if it does it casts Physick instead.