riboflavin (vitamin B₂)

Available forms
Available without a prescription
Tablets: 50 mg, 100 mg

Indications and dosages
 Riboflavin deficiency or adjunct to thiamine treatment for polyneuritis or cheilosis secondary to pellagra. Adults and adolescents age 12 and older: 5 to 30 mg P.O. daily, depending on severity.
Children younger than age 12: 3 to 10 mg P.O. daily, depending on severity.
 Microcytic anemia related to splenomegaly and glutathione reductase deficiency. Adults: 10 mg P.O. daily for 10 days.
 Dietary supplementation. Adults: 1 to 4 mg P.O. daily. For maintenance, increase nutritional intake and supplement with vitamin B complex.

Pharmacodynamics
Metabolic action: Riboflavin, a coenzyme, functions in the forms of flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) and plays a vital metabolic role in numerous tissue respiration systems. FAD and FMN act as hydrogen-carrier molecules for several flavoproteins involved in intermediary metabolism. Riboflavin is also directly involved in maintaining erythrocyte integrity.
 Riboflavin deficiency causes a clinical syndrome with the following symptoms: cheilosis, angular stomatitis, glossitis, keratitis, scrotal skin changes, ocular changes, and seborrheic dermatitis. In severe deficiency, normochromic, normocytic anemia and neuropathy may occur. Clinical signs may become evident after 3 to 8 months of inadequate riboflavin intake. Administration of riboflavin reverses signs of deficiency. Riboflavin deficiency rarely occurs alone and is commonly related to deficiency of other B vitamins and protein.

Pharmacokinetics
Absorption: Although riboflavin is absorbed readily from the GI tract, extent of absorption is limited. Absorption occurs at a specialized segment of the mucosa; drug absorption is limited by duration of drug’s contact with this area. Before being absorbed, riboflavin-5-phosphate is rapidly dephosphorylated in the GI lumen. GI absorption increases when drug is administered with food and decreases when hepatitis, cirrhosis, biliary obstruction, or probenecid administration is present.
Distribution: FAD and FMN are distributed widely to body tissues. Free riboflavin is present in the retina. Riboflavin is stored in limited amounts in the liver, spleen, kidneys, and heart, mainly in the form of FAD. FAD and FMN are about 60% protein-bound in blood. Drug crosses the placental barrier, and breast milk contains about 400 ng/ml.
Metabolism: Metabolized in the liver.
Excretion: After a single oral dose, biologic half-life is about 66 to 84 minutes in healthy people. Drug is metabolized to FMN in erythrocytes, GI mucosal cells, and the liver; FMN is converted to FAD in the liver. About 9% of drug is excreted unchanged in urine after normal ingestion. Excretion involves renal tubular secretion and glomerular filtration. Amount renally excreted unchanged is directly proportional to the dose. Drug removal by hemodialysis is slower than by natural renal excretion.

Contraindications and precautions
No known contraindications.

Interactions
Drug-drug. Hormonal contraceptives: Decreases riboflavin levels. Riboflavin dosage may need to be increased.
Propantheline bromide: Delays absorption rate of riboflavin but increases total amount absorbed. Monitor patient closely.
Drug-lifestyle. Alcohol use: Impairs intestinal absorption of riboflavin. Discourage alcohol use.

Adverse reactions
GU: bright yellow urine with high doses.

Effects on lab test results
None reported.

Overdose and treatment
No information available.

Special considerations
• RDA of riboflavin is 0.4 to 1.8 mg daily in children, 1.2 to 1.7 mg daily in adults, and 1.6 to 1.8 mg daily in pregnant and breast-feeding women.
• Obtain patient’s dietary history because other vitamin deficiencies may coexist.
• Give oral riboflavin with food to increase absorption.
• Riboflavin therapy alters urinalysis based on spectrophotometry or color reactions. Riboflavin produces fluorescent substances in urine and plasma, which can falsely elevate fluorometric determinations of catecholamines and urobilinogen.
Breast-feeding patients
• Drug crosses the placental barrier; during pregnancy and lactation, riboflavin requirements are increased. Increased food intake during this time usually provides adequate amounts. The National Research Council recommends intake of 1.8 mg daily during first 6 months of breast-feeding.

Patient education
• Teach patient about rich dietary sources of riboflavin, such as whole grain cereals and green vegetables. Liver, kidney, heart, eggs, and dairy products are also dietary sources but may not be appropriate, based on patient’s serum cholesterol and triglyceride levels.
• Advise patient to store riboflavin in a tight, light-resistant container.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use