Hydroxocobalamin, also known as vitamin B12a and hydroxycobalamin, is a vitamin found in food and used as a dietary supplement. As a supplement it is used to treat vitamin B12 deficiency including pernicious anemia. Other uses include treatment for cyanide poisoning, Leber's optic atrophy, and toxic amblyopia. It is given by injection into a muscle or vein. Side effects are generally few. They may include diarrhea, low blood potassium, allergic reactions, and high blood pressure. Normal doses are considered safe in pregnancy. Hydroxocobalamin is the natural form of vitamin B12 and a member of the cobalamin family of compounds. Hydroxocobalamin, or another form of vitamin B12, are required for the body to make DNA. Hydroxocobalamin was first isolated in 1949. It is on the World Health Organization's List of Essential Medicines. Hydroxocobalamin is available as a generic medication. Commercially it is made using one of a number of types of bacteria. Medical uses Vitamin B12 deficiency Standard therapy for treatment of vitamin B12 deficiency has been intramuscular (IM) or intravenous (IV) injections of hydroxocobalamin (OHCbl), since the majority of cases are due to malabsorption by the enteral route (gut). It is used pediatric patients with intrinsic cobalamin metabolic diseases, vitamin B12-deficient patients with tobacco amblyopia due to cyanide poisoning, and patients with pernicious anemia who have optic neuropathy. In a newly diagnosed vitamin B12-deficient patient, normally defined as when serum levels are less than 200 pg/ml, daily IM injections of hydroxocobalamin up to 1,000 μg (1 mg) per day are given to replenish the body's depleted cobalamin stores. In the presence of neurological symptoms, following daily treatment, injections up to weekly or biweekly are indicated for six months before initiating monthly IM injections. Once clinical improvement is confirmed, maintenance supplementation of B12 will generally be needed for life. Cyanide poisoning Hydroxocobalamin is first line therapy for people with cyanide poisoning. Hydroxocobalamin converts cyanide to the much less toxic cyanocobalamin. Cyanocobalamin is renally cleared. The use of hydroxocobalamin became first line due to its low adverse risk profile, rapid onset of action, and ease of use in the prehospital setting. Injectable hydroxocobalamin Injection of hydroxocobalamin is used to rectify the following causes of vitamin B12 deficiency (list taken from the drug prescription label published by the U.S. Food and Drug Administration) Dietary deficiency of vitamin B12 occurring in strict vegetarians and in their breastfed infants (isolated vitamin B12 deficiency is very