21 CFR 74.1321 - D&C Red No. 21.
(1) The color additive D&C Red No. 21 is principally 2′,4′,5′,7′-tetrabromofluorescein (CAS Reg. No. 15086-94-9), and may contain smaller amounts of 2′,4′,5′-tribromofluorescein (CAS Reg. No. 25709-83-5) and 2′,4′,7′-tribromofluorescein (CAS Reg. No. 25709-84-6). The color additive is manufactured by brominating fluorescein with elemental bromine. The fluorescein is manufactured by the acid condensation of resorcinol and phthalic acid or its anhydride. The fluorescein is isolated and partially purified prior to bromination.
(2) Color additive mixtures for drug use made with D&C Red No. 21 may contain only those diluents that are suitable and that are listed in part 73 of this chapter as safe for use in color additive mixtures for coloring drugs.
(b)Specifications. The color additive D&C Red No. 21 shall conform to the following specifications and shall be free from impurities other than those named to the extent that such impurities may be avoided by current good manufacturing practice:
(c)Uses and restrictions. The color additive D&C Red No. 21 may be safely used for coloring drugs generally in amounts consistent with current good manufacturing practice.