Vitamins
Essential organic nutrients the body cannot make in enough amounts. Fat-soluble ones (A, D) build up and can be toxic; water-soluble ones leave in the urine.
What they are
Vitamin products used to prevent or treat deficiency states: vitamin D (colecalciferol, ergocalciferol, calcitriol), vitamin A (retinol), vitamin C (ascorbic acid) and the B vitamins (thiamine, riboflavin, nicotinamide, pyridoxine).
Mechanism of action
Most B vitamins become coenzymes (thiamine pyrophosphate, FAD, NAD, pyridoxal phosphate). Vitamin C is a cofactor for collagen and an antioxidant. Vitamin D works as a hormone through a nuclear receptor, and vitamin A supports vision, epithelia and immunity.
Target: Coenzymes, cofactors and the vitamin D nuclear receptor
Drugs in this class
- ColecalciferolVitamin D3, the form the skin makes in sunlight. Liver and kidney turn it into the hormone that lets the gut absorb…Vitamin D receptor (VDR), a nuclear receptor
- ThiamineVitamin B1. Given urgently in Wernicke encephalopathy and beriberi, and with IV glucose to people with low reserves…Thiamine pyrophosphate, coenzyme of pyruvate and α-keto acid decarboxylation
- Ascorbic acidVitamin C. Needed to build collagen and absorb plant iron; the body cannot make or store it. Its lack causes scurvy.Cofactor for collagen formation; antioxidant
- PyridoxineVitamin B6. Prevents the nerve damage of isoniazid and is the antidote in isoniazid poisoning. Too much damages nerves.Pyridoxal 5'-phosphate, coenzyme of transamination and decarboxylation
- RetinolVitamin A. Prevents night blindness and xerophthalmia, and lowers measles complications in children. High doses in…Visual pigment of the retina and retinoid receptors in epithelia
- CalcitriolThe active form of vitamin D (1,25-dihydroxyvitamin D3). It works without kidney activation, so it is used in chronic…Vitamin D receptor (VDR), a nuclear receptor
- ErgocalciferolVitamin D2, made from plants and fungi. Activated like D3; prescribed for hypoparathyroidism and hard-to-treat…Vitamin D receptor (VDR), through its active metabolite
- NicotinamideA form of vitamin B3 used to treat pellagra. Unlike nicotinic acid, it does not cause flushing and does not lower…Precursor of NAD and NADP, the coenzymes of oxidation–reduction reactions
- RiboflavinVitamin B2, the building block of the coenzymes FMN and FAD. Deficiency causes sores at the mouth corners, a sore…Precursor of FMN and FAD, the flavin coenzymes
- ParicalcitolA synthetic active vitamin D analogue that lowers parathyroid hormone in chronic kidney disease. Calcium must be…Vitamin D receptor (nuclear receptor) in the parathyroid glands
Others in the class
- Paricalcitol
- Folic acid (antianaemia page)
- Vitamin B12 (antianaemia page)
- Phytomenadione (vitamin K)
Test yourself
Think of the answer, then tap the question to see it.
Which vitamins are fat-soluble and therefore can accumulate to toxic levels?
A, D, E and K.
Which vitamin deficiency causes Wernicke encephalopathy?
Thiamine (vitamin B1).
Which vitamin deficiency causes pellagra?
Niacin (vitamin B3).
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - THIAMINE HYDROCHLORIDE INJECTION, SOLUTION injection, solution (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - ERGOCALCIFEROL capsule (DailyMed (U.S. National Library of Medicine), 2026); Vitamin A: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2026); Pellagra: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2026).
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Representative model, for educational purposes only.