Mineral supplement (calcium)
Calcium is an essential mineral for bones, teeth, muscles and the heart. Calcium carbonate is the most common form of calcium supplement and also works as an antacid (relieves heartburn and indigestion). When the body does not get enough calcium from food — for example in older people or those with osteoporosis — supplements help keep bones strong.
Also known as: cálcio, calcium, carbonato de cálcio, Adcal, Calcichew
Ciprofloxacin + calcium: chelation reduces fluoroquinolone absorption.
Divalent and trivalent cations (calcium, magnesium, aluminium, iron, zinc) form insoluble chelates with fluoroquinolones in the gastrointestinal tract, reducing oral bioavailability and potentially compromising antibacterial treatment. The ciprofloxacin label recommends giving the antibiotic 2 hours before or 6 hours after magnesium- or aluminium-containing antacids and calcium, iron or zinc supplements. This precaution is especially relevant in patients taking calcium supplements during an antibiotic course (e.g., osteoporosis) — check the timing on the prescription and, if possible, give calcium with the meal furthest from the antibiotic dose.
Calcium + ciprofloxacin: chelation with reduced fluoroquinolone absorption. Separate administration by 2–6 h.
Calcium cations chelate ciprofloxacin in the gut, reducing its oral absorption.
Clinical response to antibiotic therapy.
Therapy failure, unresolved infection.
Separate calcium and ciprofloxacin dosing by at least 2 hours.
DailyMed (FDA) — approved Ciprofloxacin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c527d138-e32c-418f-9573-a3d8a796279f ; approved Calcium carbonate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=348d3dfa-6a52-4583-96e3-83c4bf2df45b — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Doxycycline + calcium: chelation reduces tetracycline absorption.
Tetracyclines, including doxycycline, form insoluble chelates with divalent and trivalent cations (calcium, magnesium, aluminium, iron, zinc) in the gastrointestinal tract, reducing oral absorption and plasma concentrations — with risk of therapeutic failure in infections such as brucellosis, rickettsioses or Lyme disease. The doxycycline label recommends separating antacids, calcium supplements and dairy products by at least 2–3 hours. Warn the patient not to take the antibiotic with milk, yoghurt or the calcium supplement, and adjust timing to maintain efficacy.
Calcium + doxycycline: chelation with reduced tetracycline absorption. Separate administration by 2–3 h.
Calcium cations chelate doxycycline, reducing its oral bioavailability.
Clinical response to antibiotic therapy.
Unresolved infection, persistent fever.
Separate dosing by at least 2 hours; give doxycycline with water.
DailyMed (FDA) — approved Doxycycline label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=fe8cd3c6-36d6-4d92-bc5c-833cd6f9cb32 ; approved Calcium carbonate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=348d3dfa-6a52-4583-96e3-83c4bf2df45b — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Iron + calcium: calcium inhibits oral iron absorption.
Calcium reduces the absorption of non-haem iron in the gastrointestinal tract, both by competing for shared transporters and by forming complexes in the lumen. In patients with iron-deficiency anaemia taking iron supplements and, simultaneously, calcium supplements (common in women and older people), iron absorption can be impaired and delay correction of the anaemia. Separate the doses by at least 2 hours (e.g., iron at breakfast and calcium at dinner), and consider vitamin C (which enhances iron absorption) with the iron dose.
Calcium + iron: calcium inhibits oral iron absorption. Separate administration by 2 h.
Calcium competes with iron for intestinal transport.
Haematological response and adherence.
Persistent iron-deficiency anaemia.
Separate iron and calcium dosing by at least 2 hours.
DailyMed (FDA) — approved Iron label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4e88a847-397b-4ddb-83d7-42c9b963a0b7 ; approved Calcium carbonate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=348d3dfa-6a52-4583-96e3-83c4bf2df45b — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Alendronate + calcium: calcium binds the bisphosphonate and prevents its absorption.
Alendronate and other oral bisphosphonates have a very low bioavailability that depends on being taken fasting, with plain water, and on having no food, drinks or other medicines in the stomach that can bind the drug. Calcium (and other cations) forms complexes with the bisphosphonate in the gastrointestinal tract, preventing its absorption and abolishing the antiresorptive effect. In practice, alendronate should be taken on waking, fasting, with a glass of water, waiting at least 30–60 minutes before eating or taking the calcium supplement (ideally calcium with the next meal).
Calcium + alendronate: calcium binds the bisphosphonate and prevents its absorption. Separate by ≥ 30–60 min (fasting).
Calcium salts form insoluble complexes with alendronate in the stomach.
Adherence and response to osteoporosis therapy.
Lack of efficacy (fractures), no other acute symptoms.
Take alendronate 30-60 minutes before calcium, in the morning on an empty stomach.
DailyMed (FDA) — approved Alendronate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ffdd2496-d253-419b-85a6-8c615f7545f1 ; approved Calcium carbonate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=348d3dfa-6a52-4583-96e3-83c4bf2df45b — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Levothyroxine + calcium: calcium reduces levothyroxine absorption.
Calcium carbonate (and other calcium salts) binds levothyroxine in the gastrointestinal tract and reduces its absorption, potentially decreasing the effect of therapy and raising TSH in patients with hypothyroidism. The levothyroxine label recommends separating calcium supplements by at least 4 hours. Levothyroxine should continue to be taken fasting, preferably 30–60 minutes before breakfast, with calcium at another time of day; when calcium is started or stopped, monitor TSH and adjust the dose if needed.
Levothyroxine + calcium: calcium reduces levothyroxine absorption. Separate by ≥ 4 h.
Calcium salts bind levothyroxine in the gut lumen.
TSH after 6-8 weeks of any dosing change.
Fatigue, weight gain, bradycardia (hypothyroidism).
Separate levothyroxine and calcium dosing by at least 4 hours.
DailyMed (FDA) — approved Levothyroxine label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c8ae9dc4-836f-4912-80d7-684fd374f40a ; approved Calcium carbonate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=348d3dfa-6a52-4583-96e3-83c4bf2df45b — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Sucralfate + calcium: sucralfate binds calcium, reducing its absorption.
Sucralfate, a polymer of sulfated sucrose with aluminium hydroxide, forms an adherent layer over the gastric mucosa and binds various drugs and cations in the gastrointestinal tract, reducing their absorption. Concomitant calcium supplements decrease calcium bioavailability. Administration should be separated by at least 2 hours (ideally sucralfate 1 hour before meals and calcium at another time), also spacing other oral medicines, since sucralfate interferes with many of them.
Sucralfate + calcium: sucralfate binds calcium and reduces its absorption. Separate by 2 h.
Sucralfate forms a film that binds cations (including calcium) in the stomach.
Effectiveness of calcium supplementation.
No acute symptoms; risk of calcium deficiency with long-term use.
Separate dosing by at least 2 hours.
DailyMed (FDA) — approved Sucralfate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1e781cc0-24ec-4028-8262-dcef9873ea1f ; approved Calcium carbonate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=348d3dfa-6a52-4583-96e3-83c4bf2df45b — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
PPI + calcium: omeprazole reduces calcium carbonate absorption.
Calcium carbonate requires an acidic gastric pH to dissolve and be absorbed; proton pump inhibitors (PPIs) such as omeprazole raise gastric pH and reduce calcium absorption from carbonate. In patients on long-term PPIs taking calcium supplements (common in osteoporosis prevention), the efficacy of supplementation can be compromised. Alternatives: use calcium citrate (pH-independent absorption), increase the dose under serum calcium monitoring, or consider the clinical impact. The interaction is of moderate relevance — do not stop PPIs without indication, but consider the most appropriate calcium salt.
PPI + calcium: omeprazole reduces calcium carbonate absorption. Consider calcium citrate or monitor.
Calcium carbonate requires gastric acid to dissolve and be absorbed; omeprazole suppresses acidity.
Serum calcium and clinical response.
No acute symptoms; risk of deficiency with long-term use.
In PPI patients, prefer calcium citrate or adjust the calcium dose.
DailyMed (FDA) — approved Omeprazole label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6ea9a6f3-b756-4cdf-b3db-f666a2c17d66 ; approved Calcium carbonate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=348d3dfa-6a52-4583-96e3-83c4bf2df45b — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Calcitriol + calcium: additive hypercalcaemia (increased risk of vitamin D toxicity).
Calcitriol increases intestinal calcium absorption; concomitant calcium supplements (carbonate) add to this effect and increase the risk of hypercalcaemia, with anorexia, nausea, constipation, weakness, polyuria and, in severe cases, nephrocalcinosis, arrhythmias and coma. This combination is common and intentional in chronic kidney disease and hypoparathyroidism, but requires monitoring of serum calcium and renal function, adjusting the calcium and calcitriol doses according to the values; also watch the interaction with thiazides, which reduce renal calcium excretion.
Calcium + calcitriol: additive hypercalcaemia. Monitor serum calcium and renal function.
Calcitriol increases intestinal calcium absorption; combined with calcium supplements serum calcium rises.
Serum calcium (Ca × P) and hypercalcaemia symptoms.
Nausea, constipation, weakness, nephrolithiasis.
Monitor serum calcium and phosphate; adjust supplementation.
DailyMed (FDA) — approved Calcitriol label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=cdcaffc6-e14e-4607-b77b-fc78a8382f60 ; approved Calcium carbonate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=348d3dfa-6a52-4583-96e3-83c4bf2df45b — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Thiazide + calcium: risk of hypercalcaemia (thiazide reduces renal calcium excretion).
Thiazides (hydrochlorothiazide) increase tubular calcium reabsorption and reduce its urinary excretion, raising serum calcium. In patients taking calcium supplements (carbonate) and vitamin D, the combination can cause hypercalcaemia — the Prontuário Terapêutico even records thiazides as contraindicated in hypercalcaemia by this mechanism. Monitor serum calcium in patients on calcium supplementation starting a thiazide, and consider reducing the calcium dose; the interaction can, however, be used favourably in renal stone disease due to hypercalciuria.
Thiazide + calcium: the thiazide reduces renal calcium excretion — risk of hypercalcaemia.
Hydrochlorothiazide reduces renal calcium elimination; with calcium supplements hypercalcaemia may occur.
Serum calcium and hypercalcaemia symptoms.
Polyuria, constipation, weakness, confusion.
Monitor serum calcium in patients on chronic supplementation.
DailyMed (FDA) — approved Hydrochlorothiazide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0789baef-3424-43ab-a3fb-4908172da565 ; approved Calcium carbonate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=348d3dfa-6a52-4583-96e3-83c4bf2df45b — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Digoxin + calcium: hypercalcaemia potentiates digoxin toxicity.
Calcium increases myocardial contractility and, at high concentrations, sensitises the heart to digoxin, increasing the risk of arrhythmias (including premature beats and ventricular tachycardias). Rapid intravenous calcium administration in digitalised patients is particularly dangerous. In patients on digoxin taking oral calcium supplements, monitor serum calcium and ECG, use the lowest effective calcium dose and correct any hypercalcaemia; also watch for signs of digitalis toxicity. The combination is safe with normal serum calcium, but the toxicity threshold falls with hypercalcaemia.
Digoxin + calcium: hypercalcaemia potentiates digitalis toxicity. Monitor ECG.
Calcium increases myocardial contractility and sensitises the heart to digoxin; intravenous calcium may precipitate arrhythmias.
Serum calcium, ECG, symptoms of digoxin toxicity.
Nausea, arrhythmias, confusion, altered colour vision.
Monitor serum calcium and signs of digoxin toxicity.
DailyMed (FDA) — approved Digoxin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=e61d2108-d871-44c0-b12a-2e61fbb56967 ; approved Calcium carbonate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=348d3dfa-6a52-4583-96e3-83c4bf2df45b — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Taking with food (acids/citrates) improves calcium carbonate absorption.
Take calcium with a meal for better absorption.
EMC-UK (MHRA) — approved Calcium carbonate SmPC: https://www.medicines.org.uk/emc/product/1295/smpc
High calcium doses with milk/dairy may cause milk-alkali syndrome.
Avoid very high calcium doses together with large amounts of milk.
EMC-UK (MHRA) — approved Calcium carbonate SmPC: https://www.medicines.org.uk/emc/product/1295/smpc
Excess urinary calcium increases the risk of renal stones.
Monitor urine calcium in patients with a history of stones.
EMC-UK (MHRA) — approved Calcium carbonate SmPC: https://www.medicines.org.uk/emc/product/1295/smpc
Calcium supplementation worsens hypercalcaemia.
Contraindicated in uncorrected hypercalcaemia.
EMC-UK (MHRA) — approved Calcium carbonate SmPC: https://www.medicines.org.uk/emc/product/1295/smpc
Calcium is essential in pregnancy; supplementation is safe at recommended doses.
Use recommended doses (about 1000 mg/day).
Compatible with breastfeeding.
No specific additional contraception.
EMC-UK (MHRA) — approved Calcium carbonate SmPC: https://www.medicines.org.uk/emc/product/1295/smpc
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Provides ionised calcium essential for bone formation, muscle contraction, nerve transmission and coagulation. As an antacid, it neutralises gastric acid quickly and durably (rebound acidification is minimal at usual doses).
Reacts with gastric hydrochloric acid forming calcium chloride, water and carbon dioxide (direct neutralisation, antacid); the calcium ion is essential for bone mineralisation and neuromuscular excitability. Vitamin D increases intestinal calcium absorption.
Oral calcium absorption depends on vitamin D and gastric acidity (carbonate requires acidic pH) — best absorbed with food; the absorbed fraction is about 25–35% and decreases with high single doses (saturable absorption).
Absorbed calcium is incorporated into bone or excreted; the balance is regulated by PTH, calcitriol and calcitonin. The carbonate is poorly metabolised; unabsorbed calcium is eliminated in faeces.
The half-life of plasma calcium is minutes to hours (rapid exchange with bone); bone residence time is years. Excretion is renal and faecal.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
