Riboflavin was evaluated for acceptable daily intake (ADI) by the
    Joint FAO/WHO Expert Committee on Food Additives in 1970 (see Annex,
    Ref. 19). A toxicological monograph was published in 1970 (see Annex,
    Ref. 20). Riboflavin-5'-phosphate has not been previously evaluated.
    However, since riboflavin-5'-phosphate is rapidly hydrolysed to yield
    riboflavin after ingestion, and riboflavin and riboflavin-5'-phosphate
    are in metabolic equilibrium after absorption, the available toxicity
    data are combined in a single monograph.



         Riboflavin is essential for all animals and many microorganisms.
    Riboflavin-5'-phosphate is the prosthetic group of flavoproteins
    involved in general cell metabolism as hydrogen acceptors. It occurs
    naturally throughout the plant and animal kingdom.

         Riboflavin-5'-phosphate or flavin mononucleotide (FMN) is rapidly
    dephosphorylated to free riboflavin by incubation with intestinal
    mucosa or intestinal juice from rats (Christensen, 1969).

         Lumichrome and lumiflavin were identified as metabolites of
    riboflavin in the rat (Yang & McCormik, 1967); hydroxyethylflavin,
    formylmethylflavin and an unknown metabolite were identified as
    metabolites in male volunteers (West & Owen, 1969).


    Special studies on mutagenesis

         Riboflavin and FMN were found not to be mutagenic to Salmonella
    typhimurium strains TA-98, TA-100, 1535, 1537 or 1538 or to
    Saccharomyces cerivisiae strain D4. Both suspension and plate
    overlay tests were conducted and assays were done with and without
    mammalian activation systems (Litton Bionetics, 1977a, 1977b).

    Special studies on reproduction

         Weanling male and female rats were fed daily doses of 10 mg of
    riboflavin for 140 days. The animals were mated and normal litters
    were obtained from the riboflavin and control groups. At three weeks
    of age the offsprings of the first generation were fed daily with
    10 mg of riboflavin. Daily feedings over periods of 140 days were

    continued for three generations. There were no differences in the
    development, growth, maturation, reproduction of treated and control
    animals. Autopsies at the end of the test period did not show any
    gross changes (Unna & Grislin, 1942).

         A group of 13 female rats were fed diets containing 100 ppm
    (0.01%) of riboflavin, for two weeks, and then bred. The diet was
    maintained during gestation and lactation. Control rats received 4 ppm
    (0.0004%) of riboflavin in the diet. The number of litters in the high
    riboflavin group was less than control. The average birth weight,
    number of young litter, and average weight at weaning was similar for
    test and control animals. However, there was an apparent decrease in
    the viability of the offspring in the high riboflavin group as a
    result of the loss of one litter (Schumacher et al., 1965).

         In another study group of young female rats (Wistar strain) were
    fed diets containing 4 or 40 ppm (0.0004 or 0.004%) of riboflavin
    during pregnancy and lactation. There were no significant differences
    in the number per litter, mortality or weight gain of offspring, in
    the groups (Le Clerc, 1974).

    Acute toxicity

    Compound             Animal  Route  (mg/kg bw)  Reference

    Riboflavin           Mouse   i.p.      340      Kuhn & Boulanger,

    salts of FMN         Mouse   Oral    6 000      Randal, 1950

                                 s.c.      800      Randal, 1950

                                 i.v.      600      Randal, 1950

                         Rat     Oral   10 000      Unna & Greslin, 1942

                                 s.c.    5 000      Unna & Greslin, 1942

                                 i.p.      560      Unna & Greslin, 1942

                         Dog     Oral    2 000      Unna & Greslin, 1942

    Sodium               Rat     Oral   10 000      Unna & Greslin, 1942
                                 s.c.      790      Unna & Greslin, 1942

                                 i.p.      560      Unna & Greslin, 1942

         The high oral LD50 in rats is probably due to poor absorption
    from the gastrointestinal tract and the low solubility of riboflavin.
    Parenteral administration of 0.6 g/kg bw leads to renal obstruction of
    pelvis and collecting tubules with crystals of riboflavin and death
    from renal failure and weight loss (Unna & Geslin, 1942).

    Short-term studies


         The monodiethanolamine salt of FMN was fed to groups of 10
    weanling female Sprague-Dawley rats five days weekly for 29 weeks at
    dose levels of 1, 4, 10 and 40 mg daily (approximately 5, 20, 50 and
    200 mg/kg bw). No effects on growth or haematology were noted at the
    5 or 20 mg/kg levels. At 50 mg/kg there was a slight decrease in
    haemoglobin concentration. At 200 mg/kg, two rats died and the
    surviving eight animals showed slight anaemia and decreased weight
    gain (Randall, 1950).


         Groups of four rabbits received 10 or 100 mg (5 or 50 mg/kg bw)
    of monodiethanolamine riboflavin by intravenous or intramuscular
    injection, five days per week for three weeks. One of the rabbits died
    with evidence of renal damage following seven intravenous injections
    at 50 mg/kg. No toxic effects were noted after intramuscular injection
    (Randall, 1951).


         Four dogs, 10 weeks of age were fed 25 mg/kg of riboflavin daily
    over a period of five months. Growth was normal and no toxic effects
    were observed. Autopsies at the end of the test period failed to
    reveal any macroscopic changes in the organs (Unna & Grislin, 1942).


         When 5-500 mg of the sodium salt of FMN was administered orally
    to human volunteers an increase in free riboflavin was noted in the
    plasma and urine. However, absorption seemed to be due to a saturable
    mechanism since an increase in urinary excretion did not occur at
    doses greater than 50 mg (Stripp, 1965).

         Increased absorption of FMN occurs in man if the substance is
    given with a meal, probably due to increased intestinal transit time.
    FMN and riboflavin are likely absorbed by a specific transport system
    in the upper gastrointestinal system. FMN may be dephosphorylated
    during absorption but then may be rephosphorylated in the mucosa,

    transported to the liver where it is again dephosphorylated to
    riboflavin, the form in which it travels in the circulation and is
    excreted. Enterohepatic recycling of riboflavin may occur (Jusko &
    Levy, 1967).

         The recommended daily dietary allowances for man is
    0.6 mg/100 Kcal. for persons of all ages engaged in normal activity
    with a daily supplement of 0.3 mg for pregnant and 0.5 mg for
    lactating women (U.S. Food & Nutrition Board, 1974).

         The recommended therapeutic doses for treatment of prevention of
    riboflavin deficiency are:


                       1968 BP and 1963 BPC   1965 USP XVII

    Therapeutic dose      5-10 mg/day           10-15 mg/day

    Prophylactic dose      1-4 mg/day            2 mg/day

         Riboflavin has been administered in large doses for the treatment
    of various clinical conditions. A seven-year-old patient with primary
    hyperoxaluria was administered 4 g riboflavin/day, for nine days. No
    toxic effects were reported (Shepard et al., 1960) In another study,
    310 patients with psoriasis were administered oral daily doses of
    10-60 mg (about 0.1-1.0 mg/kg) riboflavin-5'-phosphate or 20-1000 mg
    (about 0.3-15 mg/kg) of riboflavin for periods up to 42 months. No
    adverse effects were reported (Welsh & Ede, 1957).


         Riboflavin is an essential nutrient in man and occurs widely in
    plant and animal tissues. Riboflavin-5'-phosphate (FMN) is also
    naturally occurring. Upon ingestion, FMN appears to be rapidly
    hydrolysed to riboflavin plus phosphate. Riboflavin and riboflavin-5'-
    phosphate are in metabolic equilibrium after absorption. Some evidence
    indicates the absorption of FMN and riboflavin in man may be limited
    by a saturable mechanism in the gastrointestinal tract. In this
    monograph, safety data on riboflavin were considered supportive of the
    safety of FMN. Normal reproduction performance was reported in a three
    generation study in which rats received approximately 100 times the
    normal daily requirement. Toxic effects have not been reported in
    humans fed high levels of riboflavin.


    Estimate of acceptable daily intake for man

    (Group ADI for riboflavin and riboflavin-5'-phosphate) 0-0.5 mg/kg
    (expressed as riboflavin).


    Christensen, S. (1969) Studies on riboflavin metabolism in the rat. I.
         Urinary and faecal excretion after oral administration of
         riboflavin-5'-phosphate, Acta Pharmacol. Toxicol., 27, 37-40

    Jusko, W. J. & Levy, G. (1967) Absorption, metabolism, and excretion
         of riboflavin-5'-phosphate in man, J. Pharm. Sci., 56, 58-62

    Le Clerc (1974) Influence de la teneur du regime alimentaire en
         thiamine, en riboflavine et en vitamine B6 sur la teneur des
         tissues de la ratte en lactation et des jeunes en ces memes
         vitamines, Ann. Nutr. Aliment, 23, 111-120

    Litton Bionetics, Inc. (1977a) Mutagenicity evaluation of FDA 75-76
         riboflavin USP-FCC. Final report, LBI Project No. 2672,
         Kensington, MD, 44 pp.

    Litton Bionetics, Inc. (1977b) Mutagenicity evaluation of FDA 75-77
         riboflavin-5'-phosphate sodium FDD 00146-17-8. Final report, LBI
         Project No. 2672, Kensington, MD, 44 pp.

    Randall, L. O. (1951) Chronic toxicity of mono-diethanolamine salt of
         riboflavin monophosphoric acid ester dihydrate. Unpublished
         report of Hoffmann-La Roche, Inc. Submitted in pursuance of Fed.
         Register 38:28581 (October 15, 1973) in connection with the
         review of over-the-counter vitamin, mineral and hematinic drug

    Randall, L. O. (1950) Toxicity of mono-diethanolamine salt of
         riboflavin monophosphoric acid ester dihydrate. Unpublished
         report of Hoffman-La Roche, Inc. Submitted in pursuance of Fed.
         Register 38:28581 (October 15, 1973) in connection with the
         review of over-the-counter vitamin, mineral and hematinic drug

    Schumacher, M. F., Williams, M. A. & Lyman, R. L. (1965) Effect of
         high intakes of thiamine, riboflavin and pyridoxine on
         reproduction in rats and vitamin requirements of the offspring,
         J. Nutr., 86, 343-349

    Shepard, T. H. II et al. (1960) Primary hyperoxaluria. III.
         Nutritional and Metabolic studies in a patient, Pediatrics,
         25, 1008-1017

    Stripp, B. (1965) Intestinal absorption of riboflavin by man, Acta.
         Pharmacol. Toxicol., 22, 353-362

    U.S. Food & Nutrition Board, National Research Council (1974)
         Riboflavin, Recommended dietary allowances, 8th ed. rev.,
         National Academy of Sciences, Washington, D.C., pp. 68-69

    Unna, K. & Greslin, J. G. (1942) Studies on the toxicity and
         pharmacology of riboflavin, J. Pharmacol. Exp. Ther., 76,

    Welsh, A. L. & Ede, M. (1957) An appraisal of the therapeutic
         effects of riboflavin in psoriasis, Arch Dermatol., 76,

    West, D. W. & Owen, E. C. (1969) The urinary excretion of metabolites
         of riboflavine by man, Br. J. Nutr., 23, 889-898

    Yang, C.-S. & McCormick, D. B. (1967) Degradation and excretion of
         riboflavin in rats, J. Nutr., 93, 445-453

    See Also:
       Toxicological Abbreviations