Vitamin Drug Interactions 60

The Parkinson's-Reversing Breakthrough

Medication for Parkinson Disease

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two most clinically significant interactions are phosphate with L-dopa or isoniacid. Examine Fig. 8.36 and note that dopa decarboxylase requires PLP. This enzyme is found both centrally and peripherally. The latter includes the intestinal mucosa. The precursor to dopamine, L-dopa is indicated for the treatment of Parkinson's disease. L-Dopa is prescribed because little dopamine crosses the blood-brain barrier relative to its precursor l-dopa. A patient with Parkinson's disease prescribed L-dopa and who takes a vitamin supplement with amounts of pyridoxine greater than the vitamin's RDA can experience an in-

Dihydroxyphenethylarnine (Dopamine) Ascorbate+02 ^

Dehydroascorbate+ H20'

Dopamine ^-hydroxylase

NH3+

Norepinephrine (Norepi) S-ademosylmethionine

S-adenosylhomocysteiney

Phenylethanolamine N-methyltransferase nh34

Figure 8.36. Pyridoxal phosphate-catalyzed dopa decarboxylase.

Epinephrine (Epi)

Figure 8.36. Pyridoxal phosphate-catalyzed dopa decarboxylase.

crease in parkinsonian tremors. This is because L-dopa will undergo decarboxylation in the intestinal mucosa and never reach the locations in the brain where it is converted to the needed dopamine.

Isoniazid is widely prescribed for tuberculosis. It can chemically react with pyridoxal and pyridoxal phosphate, thus significantly reducing the availability of this coenzyme (Fig. 8.37) (61). Pyridoxine supplements commonly are recommended to prevent isoniazid-caused peripheral neuropathy, but they do not reduce the effectiveness of isoniazid.

3.8.5 Hypervitaminosis Pyridoxine. A certain mystique has built up around this vitamin, resulting in individuals' overdosing themselves with commercial vitamin supplements. Serious neurological problems have been seen in doses of 2-6 g/day for 2-40 months (62-64). Megadosing below 2 glday seems safe, but all of this information is based mostly on anecdotal reports. There is a Tolerable Upper Intake Level, but the UL to RDA ratio is a comfortable 50-60.

3.8.6 Dietary Reference Intakes.

AI (any form of vitamin B6) Infants

EAR (any form of vitamin B6) Children (1-13 years) Males (14-19 years) Females (14-19 years) Men (19-50 years) Men (51+ years) Women (19-50 years) Women (51+ years) Pregnancy Lactation

RDA (any form of vitamin B6) Children (1-13 years) Males (14-19 years) Females (14-19 years) Men (19-50 years) Men (51+ years) Women (19-50 years) Women (51+ years) Pregnancy Lactation

UL (as pyridoxine) Children (1-13 years) Adolescents (14-18 years) Adults (19+ years) Pregnancy (14-18 years) Pregnancy (19+ years) Lactation (14-18 years) Lactation (19+ years)

0.1-0.3 mglday

1.0 mglday

1.1 mg/day

1.4 mg/day

1.1 mglday 1.3 mglday

1.6 mglday

1.7 mg/day

0.5-1.0 mglday 1.3 mglday

1.2 mglday

1.3 mglday 1.7 mglday 1.3 mglday

1.5 mglday 1.9 mg/day 2.0 mglday

30-60 mglday 80 mglday 100 mglday 80 mglday 100 mglday 80 mg/day 100 mglday

Pantothenic Acid (65)

Pantothenic acid is essential and is a normal component of our diet. There has been little

Isoniazid (INH) Isonicotinic Acid Hydrazide

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