Cynomin-H

Indications

Hydroxocobalamin is a form of vitamin B12. It is used to treat and prevent vitamin B12 deficiency, including pernicious anaemia (where the stomach cannot absorb B12), deficiency after stomach or bowel surgery, and some nerve problems caused by low B12. In much higher doses, a special hospital form is used as an antidote for cyanide poisoning.

How It Works

Vitamin B12 is needed to make healthy red blood cells, to keep nerves working properly and to make DNA. When B12 is lacking, the bone marrow makes large, faulty red cells (megaloblastic anaemia) and nerves can be damaged. Hydroxocobalamin replaces the missing vitamin and is held in the body longer than Cyanocobalamin, so injections can be spaced further apart. In cyanide poisoning, it binds cyanide to form a harmless compound that leaves the body in the urine.

Dosage and Administration

Hydroxocobalamin is usually given as an injection into a muscle by a doctor or nurse, at a dose and schedule set by the doctor. A common pattern is several injections over the first weeks to refill the body's stores, followed by maintenance injections every 2 to 3 months, often for life in pernicious anaemia. The cyanide antidote is given into a vein in hospital. Oral forms, where available, should be taken as directed on the label or by your doctor.

Interactions

• Chloramphenicol may reduce the response of the blood to vitamin B12.
• Oral contraceptives can lower blood B12 levels in tests.
• Folic acid can improve anaemia but does not protect nerves when B12 is lacking, so it should not be used alone in B12 deficiency.
• Some antibiotics can make blood B12 tests unreliable.

Contraindications

• Allergy to hydroxocobalamin, cobalt or any ingredient.

Side Effects

Side effects are uncommon. They may include pain or redness at the injection site, itching, mild diarrhoea, fever, dizziness, headache, hot flushes and acne-like rash. High doses (as used for cyanide poisoning) turn the skin and urine red for some days. When treatment of severe anaemia starts, blood potassium can fall, and rarely heart rhythm changes occur.

Get urgent medical help if you have signs of a severe allergic reaction (swelling of the face, lips or throat, wheezing, collapse), chest pain, a fast or irregular heartbeat, or severe muscle weakness after an injection.

Pregnancy and Lactation

Vitamin B12 is essential in pregnancy and breastfeeding, and treating a deficiency is important for mother and baby. Hydroxocobalamin can be used when needed under medical supervision. It passes into breast milk, which is normal and beneficial.

Precautions and Warnings

• The cause of B12 deficiency should be confirmed with blood tests before treatment starts.
• In severe anaemia, potassium and blood counts are checked in the first days of treatment.
• People with pernicious anaemia need lifelong treatment; do not stop injections without medical advice.
• Report any tingling, numbness or memory problems to your doctor.

Overdose

Vitamin B12 has very low toxicity, and extra amounts are removed in the urine. If you are worried that too much was given, contact your doctor.

Therapeutic Class

Vitamin B12 preparation (haematinic); antidote for cyanide poisoning.

Storage

Store below 30°C, away from light and out of the reach of children. Keep ampoules in their carton until use. Hospital products should be stored as directed on the pack.