Occurrence of anhydrovitamin A and retro-vitamin A in pharmaceuticals; their biological potency and effect on the assay of vitamin A

Analyses of commercial samples of liquid multivitamin preparations revealed that many contained anhydrovitamin A, retro-vitamin A ether, vitamin A ether, and retro-vitamin A alcohol in varying proportions. Anhydrovitamin A and retro-vitamin A ether were present in greater amounts than the other vitamin A-derivatives. Anhydrovitamin A and retro-vitamin A ether had no measurable potency in the liver storage and vaginal smear assays, whereas retro-vitamin A acetate was 12% as potent as vitamin A. These compounds interfered with the assay of vitamin A by the United States Pharmacopeia XVI and British Pharmacopoeia 1963 methods but the interference could be eliminated by chromatography.