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Introduction
Methylcobalamin is one
of the two coenzyme
forms of vitamin B12
(the other being
adenosylcobalamin). It
is a cofactor in the
enzyme methionine
synthase which functions
to transfer methyl
groups for the
regeneration of
methionine from
homocysteine.
Pharmacokinetics
Evidence indicates
methylcobalamin is
utilized more
efficiently than
cyanocobalamin to
increase levels of one
of the coenzyme forms of
vitamin B12. Experiments
have demonstrated
similar absorption of
methylcobalamin
following oral
administration. The
quantity of cobalamin
detected following a
small oral dose of
methylcobalamin is
similar to the amount
following administration
of cyanocobalamin; but
significantly more
cobalamin accumulates in
liver tissue following
administration of
methylcobalamin. Human
urinary excretion of
methylcobalamin is about
one-third that of a
similar dose of
cyanocobalamin,
indicating substantially
greater tissue
retention.1
Clinical Applications
Bell’s Palsy: Evidence
suggests methylcobalamin
dramatically increased
the recovery time for
facial nerve function in
Bell’s palsy.2
Cancer: Cell culture and
in vivo experimental
results indicated
methylcobalamin
inhibited the
proliferation of
malignant cells.3
Research indicated that
methylcobalamin enhanced
survival time and
reduced tumor growth
following inoculation of
mice with Ehrlich
ascites tumor cells.4
Methylcobalamin has been
shown to increase
survival time of
leukemic mice. Under the
same experimental
conditions,
cyanocobalamin was
inactive.5 Although more
research is required to
verify findings,
experimental evidence
suggested
methylcobalamin might
enhance the efficacy of
methotrexate.6
Diabetic Neuropathy:
Oral administration of
methylcobalamin (500 mcg
three times daily for
four months) resulted in
subjective improvement
in burning sensations,
numbness, loss of
sensation, and muscle
cramps. An improvement
in reflexes, vibration
sense, lower motor
neuron weakness, and
sensitivity to pain was
also observed.7
Eye Function:
Experiments indicated
chronic administration
of methylcobalamin
protected cultured
retinal neurons against
N-methyl-D-aspartate-receptor-mediated
glutamate
neurotoxicity.8
Deterioration of
accommodation following
visual work has also
been shown to improve in
individuals receiving
methylcobalamin.9
Heart Rate Variability:
Heart rate variability
is a means of detecting
the relative activity
and balance of the
sympathetic/parasympathetic
nervous systems.
Methylcobalamin produces
improvements in several
components of heart rate
variability, suggesting
a balancing effect on
the nervous system.10
HIV: Under experimental
conditions,
methylcobalamin
inhibited HIV-1
infection of normal
human blood monocytes
and lymphocytes.11
Homocysteinemia:
Elevated levels of
homocysteine can be a
metabolic indication of
decreased levels of the
methylcobalamin form of
vitamin B12. Therefore,
it is not surprising
that elevated
homocysteine levels were
reduced from a mean
value of 14.7 to 10.2
nmol/ml following
parenteral treatment
with methylcobalamin.12
Male Impotence: In one
study, methylcobalamin,
at a dose of 6 mg/day
for 16 weeks, improved
sperm count by 37.5
percent.13 In a separate
investigation,
methylcobalamin, given
at a dose of 1,500
micrograms per day for
4-24 weeks, resulted in
sperm concentration
increases in 38 percent
of cases, total sperm
count increases in 54
percent of cases, and
sperm motility increases
in 50 percent of
cases.14
Sleep Disturbances: The
use of methylcobalamin
in the treatment of a
variety of sleep-wake
disorders is very
promising. Although the
exact mechanism of
action is not yet
elucidated, it is
possible that
methylcobalamin is
needed for the synthesis
of melatonin, since the
biosynthetic formation
of melatonin requires
the donation of a methyl
group. Supplementation
appears to have a great
deal of ability to
modulate melatonin
secretion, enhance
light-sensitivity,
normalize circadian
rhythms, and normalize
sleep-wake rhythm.15-20
Dosage
The dosage for clinical
effect is 1500-6000 mcg
per day. No significant
therapeutic advantage
appears to occur from
dosages exceeding this
maximum dose.
Methylcobalamin has been
administered orally,
intramuscularly, and
intravenously; however,
positive clinical
results have been
reported irrespective of
the method of
administration. It is
not clear whether any
therapeutic advantage is
gained from the non-oral
methods of
administration.
Safety, Toxicity, and
Side Effects
Methylcobalamin has
excellent tolerability
and no known toxicity.
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