Doxycycline Interactions

Iron forms an insoluble chelate complex with doxycycline in the gastrointestinal tract, dramatically reducing absorption of the antibiotic. Studies show ferrous sulfate co-administration can lower doxycycline serum levels by 80% or more, potentially leading to treatment failure.

Calcium chelates doxycycline in the gut, forming an insoluble complex that cannot be absorbed. Co-administration with calcium supplements or dairy products can reduce doxycycline absorption by 50 to 80 percent.

Magnesium ions chelate doxycycline in the gastrointestinal tract, forming an insoluble complex that markedly reduces antibiotic absorption. Magnesium-containing antacids and supplements can lower doxycycline bioavailability by up to 90 percent.