A drug that is able to efficiently remove radioactive contamination from the body would be a medical milestone.
In neighboring Iran, poisoning incidents at girls' schools sickened an estimated 13,000 mostly female students since November.
Two women, a journalist and a director of an anti-Kremlin NGO, reported symptoms that suggested possible poisoning.
An initial investigation concluded that a suspect could have poisoned the horses. There are an overall 50 horses at the horse farm.
Navalny's supporters said last month that he was suffering from significant stomach pain in jail, which they said could be a sign of some sort of slow acting poison.
The wave of suspected attacks has affected thousands of schoolgirls and provoked public anger.
One woman had survived Sararat's poisoning attempt and is now being questioned.
Nasyrova had also drugged, and robbed men while working as a dominatrix and is accused of murdering her neighbor in Russia.
Poison gas attacks on schoolgirls in Iran have shocked the world for months, from the first reports in November, at the height of the protests against the regime.
If the illness of Iranian schoolgirls is not caused by “mass sociogenic illness,” then it raises a fundamental question about the underlying reason for these incidents.