Calcium supplements may interact unfavorably with antibiotics, antacids and some osteoporosis and heart medications, according to the University of Maryland Medical Center. Some cholesterol drugs and some medications that are used to prevent seizures can reduce calcium levels in the body.
Calcium is contraindicated with intravenous administration of the antibiotic ceftriaxone due to the risk of potentially fatal damage to lungs and kidneys, says WebMD.
The osteoporosis drug alendronate is more difficult to absorb with calcium and needs to be taken a few hours before or after a calcium product, says the University of Maryland Medical Center. Calcium may thwart the absorption of antibiotics in the quinolone and tetracycline classes. More seriously, patients should not take calcium with the antibiotic gentamicin due to a risk of toxicity to the kidneys. Antacids that contain aluminum can be dangerous for patients with kidney disease when taken with calcium.
Too much calcium with the cardiac medication digoxin can increase the risk of adverse reactions to this drug. Digoxin can be ineffective in patients who are calcium deficient, patients taking dignoxin should undergo routine monitoring of their calcium levels, states the University of Maryland Medical Center. Patients who take bile acid sequestrants to lower their cholesterol may lose calcium in their urine and need to take calcium supplements. People taking some anti-seizure medications such as Dilantin and phenobarbitol may also need to supplement with calcium.