The absorption of both
tetracyclines and
iron compounds is markedly reduced by
concurrent use. The
tetracycline serum levels are reduced by 30 to 90% and their
therapeutic effectiveness may be reduced or even abolished.
The extent of the reductions depends on a number of factors.
the particular tetracycline used: tetracycline and oxytetracycline were affected
the least in one study.
the time interval between the administration of the two drugs: giving the iron 3 hours before or 2 to 3 hours after the antibacterial is satisfactory with
tetracycline, but one study found that even 11 hours was inadequate for
doxycycline.
the particular iron compound used: with tetracycline the reduction in serum
levels with ferrous sulfate was 80 to 90%, with ferrous fumarate, succinate and
gluconate, 70 to 80%; with ferrous tartrate, 50%; and with ferrous sodium
edetate, 30%. This was with doses containing equivalent amounts of elemental
iron.
Therefore separate administration by as much as possible and consider adjusting
the choice of iron compound or tetracycline.