[india-drug] Re: B6 and INH (10)

["Medicine Information Centre @ NIPER" <medinfo@niper.ac.in>]

B6 and INH (10)
******** 

Dear Dr. Kamala,

This refers to your query on pyridoxine producing neuropathy.

Large doses of the pyridoxine, administered over a long term, are known to
produce peripheral  neuropathy.

Following is the information available in this context.

1. Severe sensory neuropathy has been described in patients receiving large
doses of pyridoxine. Following  review of the possible toxicity associated
with lower doses of pyridoxine, proposals were put forward in the UK to
limit the dose freely available in dietary supplements to 10 mg daily;
products supplying up to 50 mg daily would continue to be available from
pharmacists and higher doses would only be available on prescription. In US
upper limit of 100 mg daily has been suggested. (Ref: Martindale, 33rd Ed.,
2002)

2. Although pyridoxine has generally been considered relatively nontoxic,
long-term (i.e. 2 months or longer) administration of large dosages (e.g.
usually 2 g or more daily) of pyridoxine can cause sensory neuropathy or
neuronopathy. The suggested mechanism behind this is the sensory syndrome
produced by the megadose pyridoxine may result from some anatomic
vulnerability of the neurons of the dorsal-root ganglia. (Ref: American
Hospital Formulary Service:  Drug Information, 2002).

3. Large doses of pyridoxine cause injury to the primary sensory neurons in
trigeminal and dorsal root ganglia of animals and patients subjected to
megavitamin therapy. The increased hazard to subjects with reduced renal
excretory function has been reported.(Ref: J Appl Toxicol 2004; 24(6): 497-500.)

4. The studies on children with Down's syndrome and autism, utilizing much
higher doses than are used for other therapeutic purposes, seem to indicate
relative safety if carefully monitored. Studies involving large population
groups with carpal tunnel syndrome, all adults, using 100-150 mg/day have
shown minimal or no toxicity in five- to 10-year studies. Women
self-medicating for PMS taking 500 to 5000 mg/day have shown peripheral
neuropathy within one to three years. It would appear from this
retrospective analysis that pyridoxine is safe at doses of 100 mg/day or
less in adults. In children there is not enough data to make any sort of
suggestion. Because the major neurologic complication is a peripheral
neuropathy and the causes of this condition are myriad, pyridoxine may cause
neuropathy only in patients with a pre-existing susceptibility to this
condition. (Ref: Ann N Y Acad Sci 1990;585:250-60.)

On the bases of these, it is certain that mega doses of pyridoxine will
produce peripheral neuropathy.

I hope you find the information useful.

Thanks,
Ms. Sukhpreet
Medicine Information Centre
NIPER, S A S NAGAR (PUNJAB), INDIA
http://www.niper.gov.in/medicine.htm
Contact us via email at medinfo@niper.ac.in

----------------------------------------------------------------
Disclaimer:
While every attempt has been made to provide correct & accurate information,
the Medicine Information Centre disclaims any liability, loss, injury or
damage as a consequence, directly or indirectly for the use and application
of any of the contents of this enquiry. The information given in response to
enquiry is an educational tool only and should not be taken as medical
advice.
In view of the possibility of human error or changes in medical sciences,
neither the centre nor any other party who has been involved in the
preparation or publication of this reply warrants that the information
contains herein is in every respect accurate or complete.