Drug Induced Vitamin B6 Deficiency

Vitamin B6 deficiency may result from the prolonged administration of drugs that are carbonyl-trapping reagents, and hence can form biologically inactive adducts with pyridoxal and pyridoxal phosphate. Such compounds include penicillamine, the antituberculosis drug isoniazid, and the anti-Parkinsonian drugs Benserazide and Carbidopa. Such drug-induced vitamin B6 deficiency frequently manifests as the tryptophan-niacin deficiency disease pellagra (Section 8.5.6). As discussed in Section 8.3, synthesis of the nicotinamide nucleotide coenzymes from tryptophan is pyridoxal phosphate-dependent; dietary intakes of preformed niacin seem to be inadequate to meet requirements without de novo synthesis from tryptophan, and endogenous synthesis

Table 9.4 Vitamin B6-Responsive Inborn Errors of Metabolism

Enzyme Affected

EC No.

Convulsions of the newborn Unknown

Cystathioninuria Cystathionase (see Figure 9.5)



Gyrate atrophy with ornithinuria Ornithine-S-aminotransferase



Homocystinuria Cystathionine synthase (see Figure 9.5)



Primary hyperoxaluria, type I Peroxisomal alanine-glyoxylate transaminase



Sideroblastic anemia S-Aminolevulinate synthase (1 heme synthesis)



Xanthurenic aciduria Kynureninase (see Figure 9.4)



of NAD from tryptophan seems to be more important than the utilization of dietary preformed niacin.

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