Therapeutic Uses

Pyridoxine is indicated in the treatment and prevention of known or suspected vitamin B6 deficiency, which is most likely to occur in the setting of alcoholism in developed countries. Vitamin B6 deficiency-related conditions have been reviewed by Spinneker et al.184 A hypochromic, microcytic, iron-refractory anemia, a form of sideroblastic anemia, develops because of decreased hemoglobin synthesis. Cognitive defects also develop with impairment in memory function, especially in the elderly. Convulsive seizures occur, and these are particularly problematic in vitamin B6-deficient infants. Peripheral neuropathy with paresthesia, and burning and thermal sensations is also common. The conversion of tryptophan to niacin is also PLP-dependent and vitamin B6 deficiency may, rarely, lead to pellagra.183 All of these conditions respond to increased dietary intake or administration of vitamin B6.

At least seven genetic disorders that result in a vitamin B6 deficiency syndrome in the presence of an adequate dietary intake have been identified. These result from defects in enzymes that are responsible for the bioactivation or uti lization of vitamin B6. Chronic use of estrogen-containing oral contraceptives may lead to derangements in tryptophan metabolism, a phenomenon also seen during pregnancy that is thought to result from inhibition of kinureninase (EC 3.7.1.3) by metabolites of estrogenic agents.188 Vitamin B6 levels may also be lower in these same groups. All of these conditions respond, at least partially, to treatment with large doses of pyridoxine; although the use of high doses of pyridoxine in pregnancy may not be warranted and its use with contraceptives may lead to failure.183

Certain hydrazine derivatives, when administered thera-peutically (e.g., isoniazid and hydralazine), can induce a deficiency of the coenzyme PLP by direct inactivation through the mechanism of hydrazone formation with the aldehyde functional group. Cycloserine and penicillamine may act through a similar mechanism.184 Concurrent administration of pyridoxine can avoid or resolve the relative vitamin B6 deficiency seen in each of these conditions. Administration of high doses of vitamin B6 with levodopa, alone, is not recommended because of enhanced conversion of levodopa to dopamine in the periphery resulting in decreased levodopa

Figure 28.38 • Vitamin B6-catalyzed decarboxylation and transamination by diacyl-glycine decarboxylase.

availability to the CNS. The concurrent use of a DOPA decarboxylase inhibitor mitigates this interaction and high doses of vitamin B6 are without effect on peripheral levodopa conversion. RDA amounts of vitamin B6 have not been shown to be problematic in either case.

How To Reduce Acne Scarring

How To Reduce Acne Scarring

Acne is a name that is famous in its own right, but for all of the wrong reasons. Most teenagers know, and dread, the very word, as it so prevalently wrecks havoc on their faces throughout their adolescent years.

Get My Free Ebook


Post a comment