Overview of Metabolism-
Nicotinamide and nicotinic acid are covered under genre Niacin of which Nicotinamide is essential part of NAD and NADP. NAD and NADP are required in essential biochemical reaction of the body where they act as hydrogen acceptors and donor for many enzymes. Tryptophan is the substrate for this vitamin and it can be synthesized by the body in limited amount.
• Absorption– stomach and small intestine.
• Sources- beans, milk, meat, and eggs lesser extent from cereal grains.
• The amino acid tryptophan can be converted to niacin with an efficiency of 60:1 by weight. Thus, the RDA for niacin is expressed in niacin equivalents.
• Conversion of tryptophan to niacin occurs with less efficacy in vitamin B6 and/or riboflavin deficiencies, or in the presence of isoniazid.
• The urinary excretion products of niacin include 2-pyridone and 2-methyl nicotinamide, can be measured for diagnois of Niacin deficiency.
Deficiency of Niacin:
Results in a condition called Pellagra which is a condition characterized by triad 3D- Dermatitis, Diarrhoea and Dementia.
Epidemiology and cause-
- In poor communities specially in Africa, where maize is used as staple diet. Maize chiefly contains unusable form of niacin called Niacytin. Pellagra can develop within 8 weeks if the regular diet is deficient in Niacin and Tryptophan.
- Hartnup’s Disease- a genetic disease in which there impaired absorption of AAs including tryptophan and results in Pellagra.
- Carcinoid Syndrome- Much of Tryptophan is utilized for formation of 5-HT resulting in Niacin deficiency.
- Contributing factors to Deficiency-Alcoholism, vitamin B6 deficiency, riboflavin deficiency, tryptophan deficiency
- Characterized by erythrema. Resembles sunburn over the part exposed to sunlight over the neck,limbs but sparing face giving a necklace appearance in neck called “ Casal’s Necklace” This rash is known as Casal’s necklace because it forms a ring around the neck; it is seen in advanced cases
- Vesicles, cracks, exudates and secondary infection can occur.
- Non-infective inflammation of the GIT.
- Associated with loss of appetite, generalized weakness and irritability, abdominal pain, and vomiting. Bright red glossitis.
- Delerium in acute cases
- Dementia Apathy, disorientation in chronic cases
Vaginitis and esophagitis may also occur.
1. Nicotinamide or nicotinic acid 100-200mg PO Q8hrly or Parenteral route.
Side effects may be significant with higher doses.
Response is usually rapid.
Reference- Davidson’s Principle and Practice of Medicine, Harrison’s Internal Medicine.