Drug reference

Cyanocobalamin

Vitamin · Nutritional Supplement, Hematinic

Also known as Methylcobalamin, Hydroxocobalamin, Adenosylcobalamin, Vitamin B12, Cobalamin

START

Check serum B12, homocysteine, and methylmalonic acid (MMA) levels; obtain CBC with peripheral smear. If B12 <200 pg/mL or MMA elevated, start 1000 mcg IM daily.

TYPICAL MAX

No pharmacologic ceiling; 1000 mcg IM is standard. Oral doses up to 2000 mcg/day safe.

STOP IF

Severe hypersensitivity reaction (anaphylaxis), refractory hypokalemia despite supplementation

WATCH

Monitor potassium during first 48-72h of therapy (risk of hypokalemia), CBC weekly until hematocrit normalizes, reticulocyte count at day 5-8

CDSCO approvedSchedule H (Injectable forms and high-dose oral forms usually require a prescription in India); OTC (low-dose oral supplements are widely available without prescription). For this drug, considering its common therapeutic uses and potential for parenteral administration, Schedule H for injectables and higher oral doses is appropriate for Indian context to ensure professional oversight. Low dose oral forms are often OTC in India for general supplementation, but the prompt implies a full drug entry, so scheduling for therapeutic use is relevant here. Therefore, listing Schedule H is more appropriate for its clinical utility as a drug molecule, while acknowledging OTC availability for specific low-dose formulations.ATC B03BA01

Dose laddermg/d

Renal dose adjustmenteGFR mL/min/1.73m²

KDIGO 2024 + manufacturer label

Pharmacokineticsplasma · t hours

ONSET: 15min · absorption onset
PEAK: 1h · 1 h (IM peak)
t½: 6d · 6 d (early); 400 d (terminal)
DURATION: 52.1w · Lifelong (pernicious anemia)

EXCRETION

50-98% renal within 24h; biliary/enterohepatic

route + CYP

INTERACTIONS

1 major

SEVERE in our sources

PREGNANCY

FDA PLLR: No evidence of fetal harm; vitamin B12 is essential for pregnancy. Recommended daily allowance is 2.6 mcg/day during pregnancy. Parenteral cyanocobalamin crosses the placenta and is required for fetal neural development.

FDA category + note

Top interactionssee all 5 →

Folic AcidSevereDatabaseKimi deep-research + Cla

Available in India

1,052 branded formulations and 706 fixed-dose combinations. Look up specific brands in the Drugs workspace.

Mechanism

Cyanocobalamin is a synthetic form of vitamin B12, an essential water-soluble vitamin required for DNA synthesis, erythrocyte maturation, and maintenance of myelin integrity in the nervous system. As a cofactor for methionine synthase and methylmalonyl-CoA mutase, it facilitates critical methylation reactions and conversion of methylmalonyl-CoA to succinyl-CoA (Krebs cycle entry).

Indications

Vitamin B12 deficiency (megaloblastic anemia)Pernicious anemia (autoimmune destruction of gastric parietal cells/intrinsic factor deficiency)Dietary deficiency (strict vegan diet, malnutrition)Malabsorption syndromes (post-gastrectomy, ileal disease/resection, Crohn disease affecting terminal ileum)Chronic proton pump inhibitor or H2-blocker therapy (reduced intrinsic factor secretion)Neurological manifestations of B12 deficiency (subacute combined degeneration of spinal cord, peripheral neuropathy)

Dosing

Adult: Parenteral (IM/SC/SQ): 1000 mcg daily for 6-7 days, then 1000 mcg every other day for 7 doses, then 1000 mcg every 3-4 days for 2-3 weeks, then monthly 1000 mcg for life (pernicious anemia). Oral: 1000-2000 mcg/day for deficiency; nasal spray 500 mcg weekly.
Pediatric: IM/SC: 0.2 mcg/kg (up to 1 mcg) daily for 2 weeks, then 0.2 mcg/kg 2-3 times/week until hematologic response, then maintenance 0.2 mcg/kg monthly. For severe deficiency: 1000 mcg IM daily.
Renal adjustment: No dosage adjustment required. Cyanocobalamin is renally eliminated but toxicity is not a concern at therapeutic doses.
Hepatic adjustment: No dosage adjustment required. However, hepatic disease may affect storage and metabolism of B12.
Geriatric: No specific dose adjustment required. Elderly patients have higher prevalence of atrophic gastritis and reduced intrinsic factor production — ensure adequate absorption or use parenteral route.
Max dose: 1000 mcg/dose (parenteral); 2000 mcg/day (oral); no defined toxic ceiling (water-soluble vitamin with renal excretion of excess)

Pharmacokinetics

Onset

Parenteral: rapid absorption from IM site; hematologic response (reticulocytosis) within 3-5 days.

Peak effect

IM: peak plasma within 1 hour. Oral: peak at 8-12 hours (dependent on intrinsic factor availability).

Duration

Liver stores 2-5 mg; depletion takes 2-5 years. Maintenance dosing required for life in pernicious anemia.

Half-life

6 days (early phase); 400 days (terminal, reflecting hepatic release from stores).

Bioavailability

Oral: ~1.5-2% via intrinsic factor-mediated absorption (saturable at ~1-2 mcg/dose); passive diffusion accounts for 1-5% at high doses. Parenteral: 100%.

Protein binding

Highly protein-bound in plasma via transcobalamin I (~80%) and transcobalamin II (~20%).

Metabolism

Converted in tissues to active coenzyme forms: methylcobalamin (cytosol) and adenosylcobalamin (mitochondria).

Excretion

Primarily renal: 50-98% of parenteral dose excreted in urine within 8-24 hours. Biliary excretion with enterohepatic recirculation (~3-8 mcg/day).

Contraindications

Hypersensitivity to cyanocobalamin, cobalt, or any component of the formulation
Hereditary optic nerve atrophy (Leber disease) — may accelerate vision loss
Should not be used to treat folate-deficient megaloblastic anemia without ruling out B12 deficiency (may mask neurologic damage)

Side effects

Common

Injection site pain (IM/SC)Mild diarrheaNauseaHeadacheNasal congestion (nasal spray)

Serious

Hypersensitivity reactions (anaphylaxis, angioedema, urticaria, pruritus) — rare but reported, especially with parenteral administration
Hypokalemia during initial treatment of severe megaloblastic anemia (due to intracellular potassium shift during erythropoiesis)
Thrombocytosis
Peripheral vascular thrombosis (rare)
Optic nerve atrophy acceleration in Leber disease
Pulmonary edema and congestive heart failure (rare, with rapid correction of severe anemia)

Pregnancy & lactation

Pregnancy

Lactation

Vitamin B12 is excreted in breast milk and is essential for infant development. Supplementation is recommended for lactating women, especially vegans. No adverse effects reported in breastfed infants.

Drug interactions

Folic Acid

Severe

Database

High-dose folic acid can correct the hematologic abnormalities of B12 deficiency while allowing irreversible neurologic damage (subacute combined degeneration) to progress unchecked.

Never treat megaloblastic anemia with folate alone without first ruling out B12 deficiency. Always check B12 and MMA levels before initiating folate therapy.