This was because hydroxocobalamin produced by bacteria was changed to cyanocobalamin during purification in activated charcoal columns after separation from the bacterial cultures (because cyanide is naturally present in activated charcoal). Cyanocobalamin is the form in most pharmaceutical preparations because adding cyanide stabilizes the molecule.The total world production of vitamin B12, by four companies (the French Sanofi-Aventis and three Chinese companies) in 2008 was 35 tonnes. Metabolism
The two bioactive forms of vitamin B12 are methylcobalamin in cytosol and adenosylcobalamin in mitochondria. Multivitamins often contain cyanocobalamin, which is presumably converted to bioactive forms in the body. Both methylcobalamin and adenosylcobalamin are commercially available as supplement pills. The MMACHC gene product catalyzes the decyanation of cyanocobalamin as well as the dealkylation of alkylcobalamins including methylcobalamin and adenosylcobalamin. This function has also been attributed to cobalamin reductases. The MMACHC gene product and cobalamin reductases enable the interconversion of cyano- and alkylcobalamins.Cyanocobalamin is added to fortify nutrition, including baby milk powder, breakfast cereals and energy drinks for humans, also animal feed for poultry, swine and fish. Vitamin B12 becomes inactive due to hydrogen cyanide and nitric oxide in cigarette smoke. Vitamin B12 also becomes inactive due to nitrous oxide N2O commonly known as laughing gas, used for anaesthesia and as a recreational drug. Vitamin B12 becomes inactive due to microwaving or other forms of heating. In the cytosol
Methylcobalamin and 5-methyltetrahydrofolate are needed by methionine synthase in the methionine cycle to transfer a methyl group from 5-methyltetrahydrofolate to homocysteine, thereby generating tetrahydrofolate (THF) and methionine, which is used to make SAMe.
A urethral stricture is a narrowing of the urethra, the tube connected to the bladder that allows the passing of urine. The narrowing reduces the flow of urine and makes it more difficult or even painful to empty the bladder.Urethral stricture is caused by injury, instrumentation, infection, and certain non-infectious forms of urethritis The condition is more common in men due to their longer urethra. Signs and symptoms
The hallmark sign of urethral stricture is a weak urinary stream. Other symptoms include:
Splaying of the urinary stream
Urinary frequency
Urinary urgency
Straining to urinate
Pain during urination
Urinary tract infection
Prostatitis
Inability to completely empty the bladder.Some people with severe urethral strictures are completely unable to urinate. This is referred to as acute urinary retention, and is a medical emergency. Hydronephrosis and kidney failure may also occur. Complications
Causes
Urethral strictures most commonly result from injury, urethral instrumentation, infection, non-infectious inflammatory conditions of the urethra, and after prior hypospadias surgery. Less common causes include congenital urethral strictures and those resulting from malignancy.Urethral strictures after blunt trauma can generally be divided into two sub-types;

Pelvic fracture-associated urethral disruption occurs in as many as 15% of severe pelvic fractures. These injuries are typically managed with suprapubic tube placement and delayed urethroplasty 3 months later. Early endoscopic realignment may be used in select cases instead of a suprapubic tube, but these patients should be monitored closely as vast majority of them will require urethroplasty. Blunt trauma to the perineum compresses the bulbar urethra against the pubic symphysis, causing a "crush" injury.