Methylcobalamin..diabetic neuropathy
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 methio-nine from homocysteine.
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Pharmacokinetics
Evidence indicates methylco-balamin 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
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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 homo-cysteine 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
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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.
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Safety, Toxicity, and Side Effects
Methylcobalamin has excellent tolerability and no
known toxicity.
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