Ascorbic acid (vitamin C) is an essential vitamin for healing, collagen and immunity. Severe deficiency causes scurvy. It is also used to boost iron absorption in anaemia treatment.
Also known as: Vitamina C, Redoxon
High-dose vitamin C (more than 500 mg daily) during deferoxamine therapy has been associated with cardiac dysfunction in patients with severe chronic iron overload.
Vitamin C increases the availability of mobilised iron and free iron formation, favouring oxidative injury to the already overloaded myocardium; cardiac dysfunction is described in the deferoxamine label with combined high-dose therapy.
Echocardiogram with ventricular function assessment, ferritin, liver function, fluid balance and heart failure symptoms.
Dyspnoea, oedema, orthopnoea, tachycardia, rapid weight gain.
If vitamin C deficiency is documented, do not exceed 500 mg daily (50 mg daily in children) and start only after stabilisation on deferoxamine; stop immediately if signs of heart failure appear.
FDA — Desferal (deferoxamine mesylate) for injection, Drug Interactions (vitamin C: cardiac dysfunction in severe iron overload with doses > 500 mg daily): https://www.accessdata.fda.gov/drugsatfda_docs/label/2007/016267s044lbl.pdf; Novartis — DESFERAL prescribing information; INFARMED Prontuário Terapêutico (11th ed., 2012), DEFEROXAMINE entry (p. 520).
Ascorbic acid increases oral iron absorption; the effect is often used intentionally but requires caution in iron overload states.
Reduction of ferric to ferrous iron and maintenance of its solubility in the small intestine: the Prontuário (Iron 4.1.1) states that "ascorbic acid potentiates absorption (30 mg per 200 mg of iron)".
Haematological response (haemoglobin), ferritin; iron and transferrin saturation in patients at risk of overload.
Signs of iron overload (arthralgia, hyperpigmentation, diabetes, cardiomyopathy).
Use the potentiation to correct iron deficiency anaemia; avoid pharmacological vitamin C doses in haemochromatosis, thalassaemia or other iron overload states.
INFARMED Prontuário Terapêutico (11th ed., 2012), Iron 4.1.1 — "Ascorbic acid potentiates absorption (30 mg per 200 mg of iron)".
Warfarin + vitamin C (high doses): possible INR change.
High-dose vitamin C (several grams per day) has been associated with changes in INR in patients anticoagulated with warfarin — generally a reduced anticoagulant effect, although reports vary. The mechanism is not fully clarified (possible interference with warfarin absorption or metabolism). With usual doses (up to ~500 mg/day) the risk is minimal, but in patients taking megadoses of vitamin C, monitor INR after starting, changing or stopping the supplement, and adjust the warfarin dose as needed.
Warfarin + vitamin C: high-dose vitamin C may alter INR. Monitor INR.
Very high vitamin C doses may interfere with anticoagulation (mechanism not fully clarified).
Periodic INR.
Signs of bleeding or thrombosis.
Avoid high doses (>1 g/day) without monitoring; check INR.
DailyMed (FDA) — approved Warfarin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=541c9a70-adaf-4ef3-94ba-ad4e70dfa057 ; approved Ascorbic acid (vitamin C) label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1606e29f-0e80-4069-b688-daab9cbff20a — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Taking with food reduces vitamin C gastric discomfort.
May take with or without food, according to tolerance.
EMC-UK (MHRA) — approved Ascorbic acid (vitamin C) SmPC: https://www.medicines.org.uk/emc/product/102185/smpc
Vitamin C is well absorbed with or without food; if anything, taking it with orange juice enhances simultaneous iron absorption.
Combining with orange juice improves absorption of co-administered iron (site monograph).
Site monograph (ascorbic acid — combining with vitamin C/orange juice improves iron absorption).
High vitamin C doses increase oxalate excretion and stone risk.
Avoid high doses in patients with recurrent oxalate stones.
EMC-UK (MHRA) — approved Ascorbic acid (vitamin C) SmPC: https://www.medicines.org.uk/emc/product/102185/smpc
Vitamin C increases iron absorption, which may worsen iron overload.
Use with caution in patients with iron overload.
EMC-UK (MHRA) — approved Ascorbic acid (vitamin C) SmPC: https://www.medicines.org.uk/emc/product/102185/smpc
High-dose vitamin C increases oxalate excretion — oxalate stone risk.
Avoid doses > 1 g/day with prior stones (site monograph).
Site monograph (ascorbic acid — caution in oxalate stone history).
Vitamin C is renally excreted — accumulation and oxalate in renal patients.
Reduce dose in renal impairment.
Site monograph (ascorbic acid — caution in renal impairment).
No restrictive Annex 1 entry; vitamin C is essential and supplementation at physiological/supplementary doses (up to ~1000 mg/day) is safe in pregnancy. Very high chronic doses can acidify urine and, on discontinuation, theoretically cause rebound scurvy in the newborn.
Compatible at usual doses; avoid chronic megadoses (>2000 mg/day).
Compatible; vitamin C passes into milk in amounts regulated by maternal homeostasis.
No specific additional contraception.
Prontuário Terapêutico INFARMED — 11.3.1 (Vitamins).
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Correction of vitamin C deficiency; improved iron absorption and wound healing.
Cofactor of dioxygenases (collagen prolyl and lysyl hydroxylases); reduces Fe3+ to Fe2+ in the duodenum; water-soluble antioxidant (neutralises free radicals).
Active intestinal absorption (SVCT1) with saturation at doses > 200 mg; bioavailability 70–90%.
Partial hepatic metabolism to oxalate (via dehydroascorbic acid); dose-dependent renal excretion (saturable reabsorption).
~ 1.5–2.5 h (shorter at high doses from saturated excretion).
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
