Why does Alexander Litvinenko with the sole purpose enjoy a 50/50 rework of surviving if they hold an antidote for Thallium?

I hear that Prussian Blue is an antidote for Thallium. Just wondering why that isn't working well for the ex-KGB spy they reason was poisioned. Not that I basis my life on Wikipedia but it did influence Thallium was a popular method of assination until the discovery of Prussian Blue. It seem that despite the discovery of Prussian Blue, Thallium seems to work rather well.Why does Alexander Litvinenko with the sole purpose enjoy a 50/50 rework of surviving if they hold an antidote for Thallium?
There are two things to reflect on about contained by this case:
1) Did the doctors correctly identify the poison?
2) Was Litvinenko treated soon adequate to prevent major tissue and organ lay waste to?
I'll assume that the doctors are right and that Thallium is the poison that was used contained by this case. Even contained by that case, the Thallium be in Litvinenko's system for rather some time pre-antidote. Depending on his metabolic rate, his level of fitness, and dozens of other factor specific to him, the antidote may have be given too late (not the doctors' blame, just due to circumstances). In that grip, it might not yet be clear whether Mr. Litvinenko's body is recovering or sinking further towards end. The interplay of death and rebirth of different tissue types will be a big player in this baggage.
Also, that 50/50 value is a guess, not a rock-hard number. It's just intended to represent that there is vacillation at the moment.