Alendronic Acid: Its absorption may be interfered if taken with food, nutritional supplements (calcium) or drugs (antacids) so intake of alendronic acid must be taken 30 minutes apart.
Intravenous ranitidine doubles the bioavailability of oral alendronic acid; its clinical significance is unknown.
Salicylate compounds: increased incidence of adverse events of the upper gastrointestinal tract was reported on individuals taking more than 10 mg of alendronic acid daily with salicylate compounds.
Aminoglycosides: Increased risk of hypoglycemia.
Calcium and iron salts reduce absorption of alendronic acid.
Calcium citrate and vitamin D3: Absorption of some drugs may be modified due to the presence of calcium in high doses, that is why these medications should be taken 1 or 2 hours from the calcium citrate/vitamin D3 dose.
Alcohol and caffeine intake and tobacco use in high amounts may decrease calcium citrate/vitamin D3 absorption.
Antacids containing aluminum: concomitant use may increase aluminum absorption.
Calcium channel blockers: response of verapamil et.al. to the body may be reduced.
High amounts of food intake with fiber, grains, cereals or phytates may lead to a reduced calcium absorption forming non-resolvable complexes by enteral route.
Calcitonin: Its administration must have 4 or more hours difference from the calcium citrate/vitamin D3 dose. Otherwise, hypercalcemia treatment with calcitonin may be antagonized.
Thiazide diuretics: may induce hypercalcemia by reducing calcium excretion.
Estrogens: increases calcium absorption.
Bisphosphonates: calcium citrate/vitamin D3 can decrease absorption of bisphosphonates. Patients are advised to take bisphosphonates at 30 minutes before calcium citrate/vitamin D3 dose.
Phenytoin: reduced bioavailability of both. Doses of calcium citrate/vitamin D3 and phenytoin should be taken at least 2 hours apart.
Fluoroquinolones: absorption may be reduced due to its chelation effect, thus reducing quinolone concentrations in serum and urine.
Sodium fluoride: forms non-resolvable complexes decreasing absorption of both. These medications should be administered 2 hours apart.
Cellulose sodium phosphate: its co-administration may diminish the effect of cellulose sodium phosphate for the prevention of hypercalciuria.
Potassium phosphate - sodium phosphate: concomitant use may increase the potential of calcium deposits in soft tissues if serum calcium is high.
Iron: decreases absorption of calcium supplements. These medications should be administered 2 hours apart.
Gallium nitrate: reduces calcium levels in the blood.
Calcium or magnesium-containing preparations: serum concentrations of calcium or magnesium may increase in patients with renal failure leading to hypercalcemia or hypermagnesemia.
Dairy products: excessive and long concurrent use with calcium supplements may result to milk-alkali syndrome.
Sodium bicarbonate: excessive and long concurrent use with calcium supplements may result to milk-alkali syndrome.
Tetracyclines: its absorption may be reduced by the formation of non-resolvable complexes or increase in gastric pH. These medications should be administered 1 to 2 hours apart.
Vitamin A: doses higher than 7500 RE or 25000 IU daily may stimulate bone loss and counteract the effects of calcium supplementation and may cause hypercalcemia.
Vitamin D, calciferol and calcitriol, in large doses may result to an increase intestinal absorption of calcium.
Serum phosphate: (laboratory tests) shows a decrease from normal levels on prolonged calcium administration.