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)

4.4

1.1

Gyrate atrophy with ornithinuria Ornithine-S-aminotransferase

2.6

1.13

Homocystinuria Cystathionine synthase (see Figure 9.5)

4.2

1.22

Primary hyperoxaluria, type I Peroxisomal alanine-glyoxylate transaminase

2.6

1.44

Sideroblastic anemia S-Aminolevulinate synthase (1 heme synthesis)

2.3

1.37

Xanthurenic aciduria Kynureninase (see Figure 9.4)

3.7

1.3

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

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