In reply to damowilk:
The other useful paper is the WMS guidelines published in Wilderness and Environmental Medicine:
Luks AM, McIntosh SE, Grissom CK, et al. Wilderness medical society practice guidelines for the prevention and treatment of acute altitude illness: 2014 update. Wilderness Environ Med 2014;25:S4–14. doi:10.1016/j.wem.2014.06.017
Also agrees with 125mg twice daily as the preventative dose. Some tablets are modified release so would be 250mg once daily - I prefer the normal release one though because in case it needs to be used for treatment it seems like it would act faster.
I've don't recommend to anyone to use it prophylactically but have worked with some people who decide to take it and have sometimes advised people who've already decided to take it to not go higher than this dose (the dose prescribed from travel clinics seems to vary very widely). Side effects can be troublesome for some but most people seem to tolerate it pretty well at 125mg twice daily (for me the biggest problem when I've tried it for myself is that it makes beer taste flat).