Riboflavin, also known as vitamin B2, is a water-soluble vitamin that plays a vital role in energy metabolism. It serves as a precursor for the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are essential for numerous redox reactions in the metabolism of carbohydrates, fats, and proteins. Beyond energy production, riboflavin supports antioxidant defenses, helps maintain healthy skin, eyes, and nerves, and assists in the metabolism of other vitamins such as vitamin B6 and niacin. Historically, the importance of riboflavin was recognized in the early 20th century when researchers observed that certain nutritional deficiencies caused symptoms like sore throat, cracks at the corners of the mouth, inflammation of the tongue, and skin disorders conditions later termed ariboflavinosis. In 1933, riboflavin was first isolated from milk by Paul Gyorgy and his team, and its chemical structure was elucidated by Richard Kuhn in 1935. By the 1940s, riboflavin was chemically synthesized and added to foods as a dietary supplement, marking a major advancement in preventing deficiency-related disorders. Today, riboflavin continues to be recognized as an essential nutrient, crucial for energy production and overall health.
BRAND NAMES
Ribo-100: A US brand name for oral riboflavin.
Ribo-2: Another US brand name for oral riboflavin.
B-FOLVIT Tablets: A brand that combines riboflavin with folic acid and niacinamide.
Orafast: A brand name for a riboflavin tablet.
Epioxa and Epioxa HD: Brand names for riboflavin ophthalmic (eye) solutions.
Photrexa and Photrexa Viscous: Brand names for riboflavin ophthalmic solutions used in eye procedures.
Vitaruhe: A brand name for vitamin B2 (riboflavin) supplements.
MECHANISM OF ACTION
Riboflavin functions primarily as a precursor for the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are essential for cellular metabolism and redox reactions. These coenzymes play a key role in electron transfer across various metabolic pathways, including the breakdown of carbohydrates, fats, and proteins, and are critical for energy production. Additionally, riboflavin exhibits antioxidant, anti-inflammatory, and immune-regulating properties.
PHARMACOKINETICS
Absorption
Riboflavin is mainly absorbed in the small intestine via a carrier-mediated transport system that involves the RFVT3 protein. In the diet, riboflavin is often protein-bound and must first be released and converted into its absorbable form in the stomach and upper intestine before entering the bloodstream. Typically, the body absorbs approximately 50–60% of free riboflavin from doses up to 25 mg; however, absorption efficiency declines with higher single doses due to saturation of the transport system.
Distribution
The volume of distribution for riboflavin is not a fixed, standard value like that of many conventional drugs, because it is an essential nutrient that is extensively distributed, actively transported into tissues, and metabolized into coenzymes, rather than simply diffusing passively throughout the body's water.
Metabolism
Dietary riboflavin is metabolized into its active coenzymes, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). This conversion occurs in the liver and other tissues, and these coenzymes play a critical role in numerous metabolic processes, including energy production and the metabolism of fats, carbohydrates, and proteins. Riboflavin, FMN, and FAD are absorbed through the intestinal tract and transported via the bloodstream to cells throughout the body.
Excretion
Riboflavin is primarily excreted through the urine. The body regulates riboflavin levels tightly, and any excess intake beyond tissue needs is rapidly eliminated, mostly as unchanged riboflavin. A small portion may also be excreted as its metabolites.
PHARMACODYNAMICS
Riboflavin’s pharmacodynamic effects stem from its role as a precursor to the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are vital for numerous metabolic processes. FMN and FAD function as electron carriers in a variety of redox reactions, facilitating energy production through the metabolism of carbohydrates, fats, and proteins. These coenzymes are also essential for red blood cell formation, antibody production, and the activity of various enzymes, including those involved in antioxidant defense.
DOSAGE AND ADMINISTRATION
Recommended Dietary Allowance (RDA):
Adult males: 1.3 mg/day
Adult females: 1.1 mg/day
Pregnant women: 1.4 mg/day
Lactating women: 1.6 mg/day
Therapeutic/Pharmacologic Doses:
For migraine prophylaxis: 400 mg/day orally
For riboflavin deficiency: 5–20 mg/day orally, depending on severity
Route: Oral administration is preferred; riboflavin can also be given intravenously in cases of severe deficiency or malabsorption.
Timing: Can be taken with or without food. Doses may be divided if higher amounts are required.
DRUG INTERACTIONS
Riboflavin may interact with several medications, primarily by affecting its absorption, metabolism, or excretion. Long-term use of anticonvulsants such as phenobarbital and phenytoin can increase riboflavin metabolism, potentially leading to deficiency. Chlorpromazine may reduce riboflavin absorption or increase its urinary excretion, while oral contraceptives have been reported to slightly lower riboflavin levels over time. High doses of riboflavin may also influence the efficacy of certain antidepressants, though evidence is limited. In general, riboflavin is water-soluble, and most interactions are related to changes in its metabolism or excretion rather than direct pharmacologic antagonism.
FOOD INTERACTIONS
Riboflavin has minimal direct interactions with other foods, but its stability and absorption can be notably affected by light exposure and certain cooking or food preparation methods. Taking riboflavin with meals, particularly those containing fat, generally enhances its absorption.
CONTRAINDICATIONS
Riboflavin is generally considered safe and has few contraindications. It should be used with caution in individuals with known hypersensitivity or allergy to riboflavin or any of its formulations. High-dose supplementation may also require monitoring in patients with certain metabolic disorders, although serious adverse effects are rare due to its water-soluble nature and efficient renal excretion.
SIDE EFFECTS
Nausea
Diarrhea
Stomach cramps
Increased urination
Skin rash, itching, or hives
Swelling of the face, lips, tongue, or throat
Severe dizziness
Trouble breathing
OVERDOSE
It will turn the urine a bright yellow or yellow-orange color (flavinuria).
Diarrhea
Increased urination
Nausea
Abdominal pain/gastrointestinal discomfort
In rare cases, eye irritation or increased sensitivity to light has been noted.
TOXICITY
Riboflavin toxicity is generally not a concern from either food or supplements, as the body can absorb only a limited amount at a time, with excess rapidly excreted in the urine, making it one of the safest vitamins. Although high doses are unlikely to cause serious health problems, they may occasionally result in side effects such as bright yellow or orange urine (flavinuria), nausea, or itching. No official “upper intake level” has been established, since there is no evidence of harmful effects from excessive riboflavin intake in humans.
