Absorption and elimination of D and C Red No. 28 in male F-344 rats

D and C Red No. 28 (Red 28) is a US certified color additive used in drugs and cosmetics. Little is known about the extent of systemic absorption and pharmacokinetic behavior of Red 28. Therefore, these studies were performed to determine oral bioavailability and pharmacokinetic parameters of Red 28 in male F-344 rats following single and repeated oral dosing. Rats were administered either a single i.v. dose (50 mg/kg), a low oral gavage dose (50 mg/kg), or a high oral gavage dose (500 mg/kg) of Red 28. Plasma, urine and feces samples were subjected to solid phase extraction (SPE) and analyzed by HPLC for Red 28. Regardless of the dose or route of administration, the terminal t(1/2) of Red 28 was 2.5 h. The major route of elimination was fecal excretion, with 88% (i.v.) and 98% (50 mg/kg p.o.) of the dose recovered by 96 h. Urinary excretion of Red 28 accounted for 1% of the dose following i.v. administration. No Red 28 was detected in urine after p.o. administration. Biliary excretion was determined experimentally to be the primary route of elimination for systemically available Red 28. Bioavailability following p.o. administration was very low (1-2%) and was not altered significantly by 14 days of dietary pretreatment with Red 28.