Pharmacology: Vitamin B2 is a water-soluble, B complex vitamin. It is required for tissue respiration and is also indirectly involved in maintaining erythrocyte integrity.
Vitamin B2 deficiency often accompanies pellagra and other B vitamin deficiency states and is also associated with conditions causing negative protein balance, such as chronic diarrhea, malabsorption syndrome, diabetes mellitus and chronic debilitating diseases. Deficiency is manifested by angular stomatitis, magenta tongue, fissuring of the lips and desquamation of mucous membranes, redness and scaling of the scrotum.
Pharmacokinetics: Vitamin B2 is readily absorbed from the upper gastrointestinal tract, except in the presence of malabsorption syndromes. The extent of gastrointestinal absorption is increased when the drug is administered with food and is decreased in patients with hepatitis, cirrhosis, biliary obstruction.
Vitamin B2 is inactive until phosphorylated to flavin mononucleotide (FMN) in gastrointestinal mucosal cells, erythrocytes and the liver; FMN is converted to another coenzyme, flavin adenine dinucleotide (FAD). Free vitamin B2 is present in the retina. In blood, about 60% of FAD and FMN is protein bound.
The biologic half-life is about 66 to 84 minutes following oral or i.m. administration of a single large dose in healthy individuals.
Only about 9% of the drug is excreted unchanged; the fate of the remainder is unknown. Excretion appears to involve renal tubular secretion as well as glomerular filtration. Amounts in excess of the body’s needs are excreted in urine.
Indications: Prophylaxis and treatment of vitamin B2 deficiency.
Precautions: Drug Interactions : Alcohol impairs intestinal absorption of vitamin B2.
Phenothiazines, Tricyclic Antidepressants: These drugs may inhibit the conversion of vitamin B2 to the active coenzyme form. Requirements for vitamin B2 may be increased in patients receiving these drugs.
Probenecid: The extent of gastrointestinal absorption of vitamin B2 is decreased when it is used concomitantly with probenecid.
Pregnancy and Lactation: Vitamin B2 crosses the placenta and is distributed in breast milk. Adverse effects have not been reported with intake of normal requirements.
Adverse Effects: Vitamin B2 is usually well tolerated and nontoxic. Because of its fluorescent yellow color, large doses may cause yellow discoloration of urine.
Dosage: In preventing vitamin deficiencies, adequate dietary intake is preferred over supplementation whenever possible. For a listing of food sources of vitamin B2, see Vitamin Food Sources in the Clin-Info section.
Vitamin B2 is usually given orally. It may also be given by i.m. injection or i.v. infusion as a component of multivitamin injections.
For a detailed listing of vitamin B2 and other nutrient requirements, see Recommended Nutrient Intake in the Clin-Info section.
The usual oral dose in the treatment of deficiency is 5 to 30 mg daily in divided doses for adults and 3 to 10 mg daily in divided doses for children.
VITAMIN B2 General MonographRiboflavinVitamin