Minor
Calcium carbonate × Doxycycline
Mineral supplements. Calcium×Tetracyclines
Mechanism
Doxycycline forms non-absorbable chelates with calcium in the gut (and with other polyvalent cations — magnesium, iron, aluminium). Doxycycline bioavailability falls by 50–80%.
Symptoms
Persistent infection symptoms 48–72 hours after antibiotic start, risk of clinical failure.
Management
Take doxycycline 2 hours before or 6 hours after calcium carbonate. Apply the same interval for iron, magnesium, zinc, and aluminium-containing antacids. If timing separation is impossible, choose an alternative antibiotic (amoxicillin, a cephalosporin).
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.