Hydroxocobalamin

Hydroxocobalamin, also known as vitamin B_12a 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, by pill or sublingually.

Side effects are generally few. They may include diarrhea, feeling sick, hot flushes, itchiness, low blood potassium, allergic reactions, and high blood pressure. Normal doses are considered safe in pregnancy. No overdosage or toxicity has been reported with this drug. Hydroxocobalamin is the natural form of vitamin B₁₂ and a member of the cobalamin family of compounds. It is found in both raw and cooked beef, together with other cobalamins. 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.

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 in 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.^{[citation needed]}

Although less common in this form than cyanocobalamine and methylcobalamine, hydroxocobalamine is also available as pills for oral or sublingual administration. However, one study on the treatment of children with methylmalonic acidemia and homocystinuria found oral hydroxocobalamine at 1 mg daily to be ineffective in reducing levels of homocysteine. In a trial on adult volunteers, this dose did not lead to a significant increase in serum vitamin B₁₂ levels when given thrice daily for one week. In addition, once-daily administration of 1 mg oral hydroxocobalamine caused the studied children's levels of homocysteine to increase and their levels of methionine to decrease, while the reverse happened when hydroxocobalamine was given intramuscularly.

In 2006 the FDA approved hydroxocobalamin for treating smoke inhalation, which can cause 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.

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)