SeriousTiming Sensitive
Calcium carbonate, whether taken as an antacid or calcium supplement, binds ciprofloxacin in the gut and reduces its absorption by 30 to 50 percent. Even calcium-fortified foods such as fortified orange juice or dairy can produce clinically meaningful reductions. Lower antibiotic exposure can lead to treatment failure and resistance.
Recommendation: Take ciprofloxacin at least 2 hours before or 6 hours after calcium carbonate. Avoid taking with calcium-fortified drinks or dairy in the same window.
SeriousTiming Sensitive
Calcium carbonate binds levofloxacin in the gut and reduces its absorption substantially. This applies whether calcium carbonate is taken as an antacid or as a calcium supplement.
Recommendation: Take levofloxacin at least 2 hours before or 2 hours after calcium carbonate. Do not co-administer.
SeriousTiming Sensitive
Calcium carbonate, taken as either an antacid or calcium supplement, chelates doxycycline in the gut and reduces its absorption substantially. The chelate complex is essentially nonabsorbable. Lower doxycycline levels can cause treatment failure.
Recommendation: Take doxycycline at least 2 hours before or 6 hours after calcium carbonate. Do not co-administer.
ModerateTiming Sensitive
Calcium carbonate can reduce zinc absorption when taken with the same meal or supplement dose. In a human absorption study, 600 mg of calcium as calcium carbonate reduced zinc absorption from a test meal by about 50%. This matters most when zinc is being used to correct low zinc status, support wound healing, or replace losses from poor intake.
Recommendation: Separate zinc from calcium carbonate by at least 2 hours, and preferably 4 hours when treating zinc deficiency. If calcium carbonate must be taken with meals for antacid effect, take zinc at a different meal or at bedtime if tolerated. Recheck zinc status or clinical response if deficiency symptoms are not improving.
InfoSynergy
Dietary calcium intake of around 1000-1200 mg/day is required for risedronate to fully build bone, but the calcium must not be taken at the same time as the drug. When properly separated, calcium and risedronate together produce better BMD and fracture outcomes than either alone.
Recommendation: Aim for 1000-1200 mg/day total calcium from diet plus supplements, but take calcium supplements at least 60 minutes after the morning risedronate dose, or later in the day. Split supplemental calcium into 500 mg portions for best absorption.
ModerateTiming Sensitive
Calcium carbonate can reduce iron absorption when taken at the same time. Human studies show calcium can inhibit both heme and non-heme iron absorption in single-meal settings, and calcium carbonate antacid reduced the plasma iron rise in an iron absorption study. This matters most when treating iron deficiency or in people with high iron needs.
Recommendation: Separate iron supplements from calcium carbonate by at least 2 to 4 hours. Take iron with vitamin C or a vitamin C-containing drink if tolerated, and recheck ferritin or CBC as directed. If iron levels are not improving, review calcium carbonate timing with your clinician.
NutriStack