Hydroxocobalamin

Vitamin B12 (European form of choice) and cyanide poisoning antidote

ATC code: B03BA03 (Hydroxocobalamin)

Brand names

Cyanokit, Hydroxocobalamin

Mechanism of action

Hydroxocobalamin is converted to active B12 forms (methylcobalamin and adenosylcobalamin) and serves as cofactor for methionine synthase and L-methylmalonyl-CoA mutase. Long plasma half-life (~26-31 days) gives an advantage over cyanocobalamin: fewer maintenance injections. In cyanide poisoning hydroxocobalamin binds the cyanide ion into non-toxic cyanocobalamin excreted by the kidneys. Dose 5 g IV over 15 minutes is the antidote standard (Cyanokit).

Indications

Cyanide poisoning

First line

Hydroxocobalamin as Cyanokit (SERB) is the first-line antidote for cyanide poisoning, including smoke inhalation from polymer fires. AEMPS registers Cyanokit 5 g IV. Dose: 5 g IV over 15 minutes (up to 10 g in severe poisoning). Advantage over nitrite plus sodium thiosulfate: no methaemoglobinaemia or hypotension, so safe with concurrent carbon monoxide poisoning. Colours skin, mucosa and urine red or pink for 1-7 days – not concerning, but distorts lab tests (bilirubin, creatinine, magnesium).

Sources

AEMPS: Ficha técnica de Cyanokit (hidroxocobalamina) (2023)

Vitamin B12 (cobalamin) deficiency

First line

Hydroxocobalamin is the European form of choice for treating confirmed vitamin B12 deficiency in patients with pernicious anaemia, after gastric or ileal resection, and in vegetarians and vegans with confirmed deficiency. 2024 and 2014 recommend induction 1000 μg IM three times weekly for 2 weeks then maintenance 1000 μg every 2-3 months for life. Advantage over cyanocobalamin: fewer injections due to longer half-life. With neurological symptoms (subacute combined degeneration), induction may be extended until neurological recovery or plateau.

Sources

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

Anti-aging and longevity

Not recommended

Hydroxocobalamin is a form of vitamin B12 used to treat B12 deficiency and the anemia linked to it. Marketers promote it for anti-aging and longevity as a way to "rejuvenate" and slow aging, but no convincing benefit has been shown for that use – there is no solid evidence that taking it for longevity helps people whose B12 levels are normal. When B12 is already adequate, extra doses do not produce an anti-aging effect. What actually affects aging is sleep, diet, physical activity, not smoking, and keeping blood pressure and blood sugar in check; B12 is worth supplementing only when lab tests confirm a deficiency.

Sources

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Official sources

Direct links to regulator labels. Open in a new tab.

AEMPS / CIMA

Spanish Medicines Information Centre (CIMA)

Label dated: 01/17/2025

FDA / DailyMed

FDA — DailyMed Drug Labels

Label dated: 04/27/2023

Safety

Contraindications

Hypersensitivity to hydroxocobalamin
Leber hereditary optic neuropathy

Serious adverse effects

Anaphylactic reactions (rare)
Acute kidney injury with urinary oxalate crystals (reported after high-dose Cyanokit)
Lab test interference for 1-2 weeks (bilirubin, creatinine, magnesium, total protein, ALT)

Common adverse effects

Reddish-pink discolouration of skin, mucosa and urine (1-7 days after Cyanokit)
Acneiform rash
Nausea
Transient hypertension with rapid IV administration
Headache

PregnancyFDA A

FDA Category A at physiological and replacement doses. AEMPS allows use in pregnancy for confirmed deficiency. In cyanide poisoning of a pregnant woman Cyanokit is given without hesitation: cyanide threatens the lives of both mother and fetus more than the antidote.

Breastfeeding

Compatible (Hale L1) at physiological doses. After a 5 g antidote dose, milk concentration is markedly elevated; AEMPS recommends interrupting breastfeeding for 7-14 days with expression and disposal.

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Frequently asked

What is Hydroxocobalamin used for?

Hydroxocobalamin is evaluated for the following indications with varying evidence strength: Vitamin B12 (cobalamin) deficiency (evidence tier A), Cyanide poisoning (evidence tier A), Anti-aging and longevity (evidence tier D). See the full indication matrix with dosing and citations above on this page.

What are the side effects of Hydroxocobalamin?

Common side effects of Hydroxocobalamin (≥ 1 in 100): Reddish-pink discolouration of skin, mucosa and urine (1-7 days after Cyanokit), Acneiform rash, Nausea, Transient hypertension with rapid IV administration, Headache. See the Safety section for uncommon and serious reactions.

Is Hydroxocobalamin safe during pregnancy?

FDA category A. FDA Category A at physiological and replacement doses. AEMPS allows use in pregnancy for confirmed deficiency. In cyanide poisoning of a pregnant woman Cyanokit is given without hesitation: cyanide threatens the lives of both mother and fetus more than the antidote.

Is Hydroxocobalamin compatible with breastfeeding?

Who should not take Hydroxocobalamin?

Hydroxocobalamin is contraindicated in: Hypersensitivity to hydroxocobalamin; Leber hereditary optic neuropathy. Full list in the Safety section.

Mechanism of action

Indications

Cyanide poisoning

First line

Sources

AEMPS: Ficha técnica de Cyanokit (hidroxocobalamina) (2023)

Vitamin B12 (cobalamin) deficiency

First line

Sources

Safety

Contraindications

Hypersensitivity to hydroxocobalamin
Leber hereditary optic neuropathy

Serious adverse effects

Anaphylactic reactions (rare)
Acute kidney injury with urinary oxalate crystals (reported after high-dose Cyanokit)
Lab test interference for 1-2 weeks (bilirubin, creatinine, magnesium, total protein, ALT)

Common adverse effects

Reddish-pink discolouration of skin, mucosa and urine (1-7 days after Cyanokit)
Acneiform rash
Nausea
Transient hypertension with rapid IV administration
Headache

PregnancyFDA A

Breastfeeding

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Frequently asked

What is Hydroxocobalamin used for?

What are the side effects of Hydroxocobalamin?

Is Hydroxocobalamin safe during pregnancy?

Is Hydroxocobalamin compatible with breastfeeding?

Who should not take Hydroxocobalamin?

Hydroxocobalamin is contraindicated in: Hypersensitivity to hydroxocobalamin; Leber hereditary optic neuropathy. Full list in the Safety section.