Calcium (calcium carbonate) is an essential mineral for bones, teeth, muscle contraction and clotting. It serves as a supplement in osteoporosis and pregnancy, and as an occasional antacid in heartburn.
Also known as: Carbonato de cálcio, Calcionat
Oral calcium supplementation in patients on digoxin should be monitored: changes in serum calcium modify sensitivity to digitalis toxicity.
Hypercalcaemia potentiates digitalis toxicity (Prontuário 3.1.1: "hypercalcaemia situations" among digitalis contraindications); continuous oral supplements may raise it.
Serum calcium, potassium, digoxin level, ECG.
Nausea, colour vision changes, arrhythmias, confusion.
Monitor calcium and potassium in patients on chronic supplements; ECG if digitalis toxicity symptoms appear.
INFARMED Prontuário Terapêutico (11th ed., 2012), Digitalis 3.1.1 — hypercalcaemia contraindicates digitalis; DailyMed — Digoxin Tablet label [RLD Lanoxin]: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=dfac7f13-28be-423d-9389-9089da29da17
Calcium carbonate reduces levothyroxine absorption by chelation, potentially causing undertreated hypothyroidism if taken together.
Divalent cations chelate thyroxine in the gut (same family as Annex 7 Iron: "Thyroxine" with reduced absorption; Ca2+ antacids likewise).
TSH and free T4 6–8 weeks after any regimen change.
Fatigue, weight gain, oedema (hypothyroidism).
Separate doses by at least 4 hours; reassess TSH/free T4 after 6–8 weeks.
INFARMED Prontuário Terapêutico (11th ed., 2012), Annex 7 — Iron/Antacids: "Thyroxine" with reduced absorption by cations; DailyMed — Levothyroxine Sodium Tablet label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=255ad500-6656-4cd0-b4d1-10cc22f9e61b
Calcium is the physiological antidote of magnesium: in MgSO4 toxicity IV calcium gluconate reverses its effects, but mixing them in the same infusion line precipitates.
Direct physiological antagonism: Ca2+ competes with Mg2+ at NMDA channels and acetylcholine release; chemically, Ca2+ forms insoluble salts (MgSO4/gluconate profile: "NEVER mix with sodium bicarbonate"; same rationale for concentrated MgSO4 in the same line).
Patellar reflexes, respiratory rate, serum Mg2+ and Ca2+ (if toxicity).
Muscle weakness, respiratory depression, absent reflexes.
In eclampsia: have IV calcium gluconate available as the MgSO4 antidote; never give in the same line; in chronic oral supplementation, separate doses.
INFARMED Prontuário Terapêutico (11th ed., 2012), Magnesium sulfate entry (calcium antagonism); EMC-UK — Magnesium Sulfate/Calcium Gluconate (documented physiological antagonism in eclampsia): https://www.medicines.org.uk/emc/product/6265/smpc
Sodium bicarbonate and calcium must NEVER be given in the same infusion line: calcium carbonate precipitation with embolisation risk.
Direct chemical reaction: Ca2+ + HCO3− → insoluble CaCO3 (precipitate), especially at high pH; documented in the calcium gluconate profile and IV labels.
Check line patency; ECG during electrolyte corrections.
Visible precipitate in the line, embolism (rare), arrhythmias.
Use separate lines with a saline flush between drugs; never Y-mix.
DailyMed — Calcium Gluconate Injection and Sodium Bicarbonate Injection labels (infusion incompatibilities): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=16307c00-d0d5-4e05-821f-17b0c1a29fc9
Calcium carbonate needs gastric acid to dissolve — taking it with a meal improves absorption and reduces constipation.
Take with a meal (citrate does not require it, but carbonate is the usual form).
Site monograph (calcium — take with meal improves absorption); DailyMed Os-Cal (calcium carbonate).
Calcium supplementation in established hypercalcaemia worsens it (arrhythmias, dehydration, coma).
Measure calcium before supplementing; discontinue if hypercalcaemia.
Site monograph (calcium — do not exceed 2000–2500 mg/day; avoid with prior stones without assessment).
Unassessed supplementation raises stone risk in predisposed patients.
With prior renal stones, avoid supplementation without assessment (site monograph).
Site monograph (calcium — with prior stones avoid supplementation without assessment).
No restrictive Annex 1 entry; calcium supplementation (1.5–2 g/day) in pregnancy reduces the risk of pre-eclampsia in women with low dietary intake (WHO) and is standard practice. IV calcium gluconate is the antidote for hypermagnesaemia and calcium-channel-blocker poisoning — safe in pregnancy when indicated.
Compatible; prophylactic oral supplementation and therapeutic IV use are safe when indicated.
Compatible; calcium passes into milk in regulated amounts.
WHO — WHO recommendation on calcium supplementation in pregnant women (2013, updated 2020). Prontuário Terapêutico INFARMED — 11.3.3 (Mineral salts).
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Correction of hypocalcaemia; reduced bone resorption and PTH at supplementary doses; gastric HCl neutralisation (antacid).
Ca2+ exerts structural (bone hydroxyapatite), signalling (muscle contraction, exocytosis, clotting via factor IV) and neuronal excitability modulation functions.
Calcium carbonate: 25–40% absorption (better with meal and vitamin D); dissolves in acidic gastric medium (reduced on PPIs).
No metabolism; renal (99% reabsorbed), faecal and sweat excretion; regulated by PTH and vitamin D.
~ 3–5 h (oral; dose- and bone distribution-dependent).
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
