What are the contraindications to B12 (cobalamin) injections in patients with various medical conditions, including allergies, Leber's optic neuropathy, pregnancy, breastfeeding, kidney disease, liver disease, and those taking medications like chloramphenicol (antibiotic)?

Contraindications to B12 Injections

The absolute contraindication to B12 injections is a history of hypersensitivity to cobalt, vitamin B12, or any vaccine component (including yeast in some formulations), or a previous anaphylactic reaction to B12 administration. 1, 2

Absolute Contraindications

• Known hypersensitivity to cobalt or vitamin B12 is an absolute contraindication to all forms of B12 injections 1, 2
• Previous anaphylactic shock after parenteral B12 administration (anaphylactic shock and death have been reported) 1
• Early Leber's disease (hereditary optic nerve atrophy) is a contraindication specifically to cyanocobalamin injections, as patients with this condition have suffered severe and swift optic atrophy when treated with cyanocobalamin 1, 3

Serious Warnings and Precautions

Patients Requiring Special Consideration:

• Severe renal impairment (GFR <50 mL/min): Cyanocobalamin should be avoided in these patients due to increased risk of cardiovascular events; use methylcobalamin or hydroxocobalamin instead 4

• Premature neonates and patients with impaired kidney function: Products containing aluminum (some B12 formulations) may reach toxic levels with prolonged parenteral administration, as aluminum accumulates at levels associated with central nervous system and bone toxicity at doses >4-5 mcg/kg/day 1

• Products containing benzyl alcohol: These are contraindicated in premature infants due to association with fatal "Gasping Syndrome" 1

• Severe megaloblastic anemia: Hypokalemia and sudden death may occur when treated intensely; close monitoring is essential 1

Recommended Safety Measures:

• Intradermal test dose is recommended before cyanocobalamin injection in patients suspected of being sensitive to the drug 1

• Emergency preparedness: All B12 injections should be administered in settings where personnel are trained to recognize and manage acute hypersensitivity reactions, with emergency equipment and medications immediately available 5

Conditions That Are NOT Contraindications

The following are not contraindications to B12 injections:

• Pregnancy (pregnancy is not a contraindication; limited data show no apparent risk to the fetus) 6
• Breastfeeding 6
• History of autoimmune disease (MS, Guillain-Barré syndrome, rheumatoid arthritis, systemic lupus erythematosus) 6
• Mild to moderate renal impairment (≥30 mL/min creatinine clearance) 6
• Mild hepatic impairment (total bilirubin >ULN to 1.5x normal) 6

Medication Interactions to Consider

While not absolute contraindications, chloramphenicol and other medications may interfere with B12 response and should be used cautiously 6. However, this does not preclude B12 injection administration.

Clinical Algorithm for Safe Administration

1. Screen for absolute contraindications: History of anaphylaxis to B12, cobalt allergy, or early Leber's disease 1, 2
2. Assess renal function: If GFR <50 mL/min, use methylcobalamin or hydroxocobalamin instead of cyanocobalamin 4
3. Consider intradermal test dose in patients with suspected sensitivity 1
4. Ensure emergency preparedness before administration 5
5. Monitor for hypokalemia in patients with severe megaloblastic anemia during initial treatment 1