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B12 injection Vs oral administration

B12 injections vs oral administration
The Vitamin B12 is available for injection as well as oral administration. There are also combinations of the vitamin B12 with other vitamins and minerals that can be given orally or parenterally. The choice of a preparation always depends on the cause of the deficiency. Although oral preparations may be used to supplement deficient diets, they are of limited value in the treatment of patients with deficiency of intrinsic factor or ileal disease or after gastrectomy. Even though small amounts of vitamin B12 may be absorbed by simple diffusion, the oral route of administration cannot be relied upon for effective therapy in the patient with a marked deficiency of vitamin B12 and abnormal hematopoietic or neurological deficits. Therefore, the preparation of choice for treatment of the vitamin B12 deficiency state is cyanocobalamin, a vitamin b12 injection and it should be administered by intramuscular or subcutaneous injection. 
Cyanocobalamin is the most widely used form of the vitamin B12 injection, and has hematopoietic activity apparently identical to that of the anti-anemia factor in purified liver extract. Hydroxycobalamin, another vitamin B12 injection is equally as effective as cyanocobalamin, and they share the cobalamin molecular structure. To deal with acute situations, Vitamin  B12 injections are given daily for several weeks, then twice a  week for a month, and monthly thereafter.
Cyanocobalamin is administered in doses of 1 to 1000mcg. Tissue uptake, storage, and utilization depend on the availability of transcobalamin II. Doses in excess of 100mcg are cleared rapidly from plasma into the urine, and administration of larger amounts of the vitamin B12 will not result in greater retention of the vitamin. Administration of 1000mcg is of value in the performance of the Schilling test. After isotopically labeled vitamin B12 is administered orally, the compound that is absorbed can be quantitatively recovered in the urine if 1000mcg of cyanocobalamin is administered intramuscularly. This unlabeled material saturates the transport system and tissue binding sites, so that more than 90% of the labeled and unlabeled vitamin is excreted during the next 24 hours. Usually, the Vitamin B12 injections must be taken for life. It's difficult for the people to take monthly B12 injections, so other forms are being investigated. In Europe, a nasal spray form of the vitamin b12, hydroxocobalamin is showing promise and is expected to reach the U.S. soon.
Many Vitamin B12 injections (Cyanocobalamin) under various Brand names such as Cobal, Cyanoject, Cyomin, Vibal, Vitamin B-12 etc are available in the market. Vitamin B12 injections help the body use fat and carbohydrates for energy and make new protein. It is also important for normal blood, cells, and nerves. Most people get enough of the vitamin B12 in their diet, but a deficiency may occur in certain health conditions (e.g., pernicious anemia), poor nutrition, stomach/intestinal problems, infection, (cancer). Serious vitamin B12 deficiency may result in anemia, stomach problems, and nerve damage.
Another way or route of providing the vitamin B12 is through the oral route. This route is not is not used nowadays as injectables are very much superior to oral medication.  The only indication for oral therapy is when the patient has any bleeding manifestations like hemophilia. In this condition injections can lead to profuse bleeding. Because a small fraction of cobalamin can be absorbed passively through mucous membranes even when there is complete failure of physiological IF-dependent absorption, large daily oral doses (1000–2000g) of cyanocobalamin can be used in PA for replacement and maintenance of normal cobalamin status. But nowadays oral therapy is replaced by sublingual route for tackling this type of conditions.
Gastrointestinal absorption of vitamin B12 depends on the presence of sufficient intrinsic factor and calcium ions. Vitamin B12 is bound to intrinsic factor during transit through the stomach; separation occurs in the terminal ileum in the presence of calcium, and vitamin B12 enters the mucosal cell for absorption. It is then transported by the transcobalamin binding proteins. A small amount (approximately 1 percent of the total amount ingested) is absorbed by simple diffusion, but this mechanism is adequate only with very large doses. Intrinsic factor deficiency causes pernicious anemia, which may be associated with subacute combined degeneration of the spinal cord. In these conditions of absent intrinsic factor Oral absorption is considered too unreliable in patients with pernicious anemia or other conditions resulting in mal-absorption of vitamin B12.
A number of multivitamin preparations are marketed either as nutritional supplements or for the treatment of anemia. Many of these contain up to 80g of cyanocobalamin without or with intrinsic factor concentrate prepared from the stomachs of hogs or other domestic animals. One oral unit of intrinsic factor is defined as that amount of material that will bind and transport 15g of cyanocobalamin. Most multivitamin preparations supplemented with intrinsic factor contain 0.5 oral units per tablet. While the combination of oral vitamin B12 and intrinsic factor would appear to be ideal for patients with an intrinsic factor deficiency, such preparations are not reliable. With prolonged therapy, some patients become refractory to oral intrinsic factor, perhaps related to production of an intra-luminal antibody against the hog protein. Patients taking such preparations must be reevaluated at periodic intervals for recurrence of pernicious anemia.
 If oral therapy is used, it is important to monitor compliance. In elderly it is not uncommon that they may forget to take their daily doses of the vitamin b12. Since the oral vitamin b12 dosage should be given daily, it has got less compliance than vitamin B12 injections which are given only once monthly.