I vaguely remember this fantasy-esque miniseries (or was it a made for TV movie?) that featured a society where some of the worst criminals were punished with immortality along with imprisonment as a form of ultimate punishment. Basically, if I recall correctly, being immortal was seen as a curse and once you were immortal you could be kept imprisoned by other immortals for millennium or longer.
Offenders were made immortal by being strapped to a chair with their mouth forced open and some kind of lizard-like humanoid would spit/excrete some kind of mucusy substance into their mouth, kind of gross. I only saw a few parts of the show so I could be misremembering or misunderstanding any or all of it. But I do distinctly remember immortality being administered as a punishment to at least one character.
I think this miniseries or TV movie was made some time in the 90s, but it could be late 80s for all I know.