PROBLEM TO BE SOLVED: To provide a stable pharmaceutical aqueous solution of cyanocobalamine suitable for intranasal administration in which the bioavailability of cyanocobalamine in the case of intranasal administration is at least about 5% relative to intramuscular injection of cyanocobalamine and a pharmaceutical kit for nasal drug delivery.SOLUTION: A cyanocobalamine aqueous solution comprising cyanocobalamine and water has a viscosity less than about 1000 cPs allowing nasal administration of the cyanocobalamine solution in an amount sufficient to increase the average ratio of vitamin B12 in the cerebrospinal fluid (CSF) to vitamin B12 in the serum, (B12 CSF)/(B12 serum)×100, to at least about 1.1.
