A 2-year-old boy is brought to the emergency department due to sudden-onset facial redness. The symptoms were first noticed by the parents about 1 hour ago. The mother also noticed an opened bottle of a vitamin supplement with a few capsules spilled on the floor. The child has no known medical conditions and takes no medications. Vital signs are normal. Physical examination shows facial flushing. The rest of the examination is unremarkable. This patient most likely ingested a vitamin that has which of the following biochemical functions?
Acute facial flushing following accidental vitamin ingestion is highly suggestive of niacin (vitamin B3) toxicity. Niacin is a water-soluble vitamin and the precursor for NAD (nicotinamide adenine dinucleotide) and NADP, which are both cofactors for key enzymes involved in the synthesis and metabolism of carbohydrates, protein, and fatty acids.
Niacin supplementation is effective in the treatment of hyperlipidemia. At high doses, niacin increases the activity of lipoprotein lipase, which promotes delivery of fatty acids to tissues for storage or metabolism. Adverse effects of niacin include cutaneous vasodilation, flushing, and pruritus due to increased prostaglandin production in dermal Langerhans cells. Pretreatment with nonsteroidal anti-inflammatory drugs (NSAIDs), like aspirin, prior to the administration of niacin decreases prostaglandin production and minimizes flushing.
(Choice A) Thiamine (vitamin B1) is a coenzyme for transketolase in the pentose phosphate pathway. Thiamine deficiency leads to wet beriberi (cardiac failure), dry beriberi (peripheral neuropathy), and Wernicke encephalopathy (oculomotor dysfunction, ataxia, and encephalopathy); clinically relevant toxicity does not occur.
(Choice B) Vitamin C is a coenzyme for the hydroxylation of prolyl and lysyl residues. Vitamin C deficiency leads to scurvy (weakness, fatigue, easy bruising, bleeding gingivae). Large doses of vitamin C are associated with kidney stones and false-negative stool guaiac results.
(Choice C) Pantothenic acid (vitamin B5) is a component of coenzyme A, which is a cofactor for key enzymes involved in acetylation reactions; there is no known toxicity.
(Choice D) Riboflavin (vitamin B2) is the precursor for flavin adenine dinucleotide (FAD) production; excess vitamin B2 is not associated with toxicity.
Educational objective:
Niacin (vitamin B3) is the precursor for NAD and NADP. Niacin toxicity leads to increased prostaglandin production, which causes cutaneous vasodilation, flushing, and pruritus that may be avoided by pretreating with nonsteroidal anti-inflammatory drugs.