Eh, just off the top of my head, I read in the Chicago Tribune, possibly yesterday, that it depends on what strain of anthrax you’re dealing with. The Russian strain is resistant to tetracycline and penicillin, because the Russians spent some time Back In The Days creating a strain that would be resistant to these two common antibiotics. So Cipro and its generic equivalents are the antibiotics of choice for this strain.
But other strains, like the Ames Strain, are susceptible to tetracycline and penicillin.
Specifically as to why they recommend doxycycline rather tahn tertracyline, I imagine it’s a side effects issue. Tetracyline is notorious for causing stomach upset, and should be given to young people, because it causes permenant black teeth (really). There is some evidence in mice that tetracycline, but not doxycycline, can cause neurological abnormalities in developing embryos if the patient is pregnant.
So even though both antibiotics kill a very similar range of organisms, and I’m sure tetracylcline would work perfectly well against anthrax, there are reasons to recommend doxycyline for widespread usage.
Actually my PDR (which like I said is from '97 so may be outdated) indicates the same side effects (teeth included) for tetracycline as doxycycline. Both are not recommended for kids under 9 years old.