I did alot of research on this subject and I can tell you that you could take 10g without doing your liver bad. Liver panel could rise a bit, but if you stop your B3 intake shortly before your doctors visit your liver panel should show just fine values.
'm too lazy now to look up for studies and sources for this claim, but as mentioned Dr. Hoffer as the Niacin pioneer made studies and gave alot of infos on the subject and other mds followed his example.
btw, B3 isn't much of a great detoxifier imho, though Dr. Yu had me convinced of the opposite at the beginning http://www.youtube.com/watch?v=47UyvsCQ-mk
But B3 has alot of other advantages like optimizing blood lipids, calming nerves, good for psychiatric illnesses, HGH release/Hormonal balance and through helping mitochondrial function it could indirectly help your body detox. Its my favourite nutrient after Iodine, Dr. Saul is a strong supporter of it and worked with Dr. Hoffer personally www.doctoryourself.com