Hi David, Generally we use these formulations

Hydroxocobalamin

Cyanocobalamin

Methylcobalamin

All three types are considered `Vitamin B12`, they are NOT all the same and using the right one can be a critical decision.

Cyanocobalamin is probably the most commonly used in the medical world and is often given as `B12 Shots` . But  cyanocobalamin require a higher dosage for the same effectiveness of hydroxycobalamin, but it is Entirely Ineffective for several different conditions related to vitamin B12 deficiency. 

While hydroxocobalamin is preferred over cyanocobalamin, another formulation called methylcobalamin is actually now said to be the BEST choice. Technically a `coenzyme` of vitamin B12, it is almost never used despite being effective, readily available, inexpensive and available in both sublingual preparations and injectable form.

Hi Anjali, 

Thanks for your answer - I am planning to pay for the manufacturing of a vitamin B12 transdermal patch.  In your expert opinion, should I use hydroxocobalamin or 

HI David, Firstly I am not an expert in this field. But , I think you should try out with the derivative Methylcobalamin prepn. The other parts like the Penetration properties, molecular size and the penetration enhancers should be considered beforehand. You are going to manufacture the prepn so you can concentrate on these factors.

Some of the patents are already taken for these prepn of transdermal patches. So check those also.

What you use depends on why the person is B12 deficient. If dietary intake is low, because of poverty or veganism, then cheap oral supplements will do. Various drugs, including Amitriptyline and proton pump inhibitors cause deficiency, in which case the solution is to stop the drugs. Coeliac disease may be involved, in which case avoid gliadin. Auto-immune disease, leading to deficiency of intrinsic factor, perhaps due to molecular mimicry involving helicobacter pylori, may be involved. Parasites may be causal. Gastric surgery may be. There may be polymorphisms involving methylation, in which case use methylcobalamin.

Methylcobalamin is abetter choice specially in cases of dietary deficiency as ora supplements.

It is a water soluble vitamin. penetration through the skin may not be sufficient to reach RDA.

I think methyl cobalamin

Adenosylcobalamin is more expensive and has a different function from methylcobalamin; it is a different chemical.

Hydroxylcobalamin is broken down into methyl, but is said to be stored longer in the body.

Methyl is the most popular, dont even consider cynocobalamin