IIRC the addition of the hydroxy to the drug means it's going to be more water-soluble so it would be easier to excrete in urine and flush it out of the system,

IIRC the addition of the hydroxy to the drug means it's going to be more water-soluble so it would be easier to excrete in urine and flush it out of the system, which would count as "less toxic" if you squint when reading the paper I haven't seen any detailed discussions of the differences in toxicity, but one physician made a comment to that effect.