Blackwell's Five-Minute Veterinary Consult: Reptile and Amphibian. Javier G. Nevarez

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       In vertebrates, the vitamin A forms are trans‐retinyl esters, trans‐retinol, ‐retinal and ‐retinoic acid (99% of all vitamin A present in the body), while the major dietary provitamin A carotenoid is beta carotene.

       The all‐trans‐vitamin A isomers are the only forms used physiologically.

       The liver absorbs and stores preformed vitamin A; at a certain point, storage capacity is reached and toxicity occurs. Other storage sites include adipose tissue, lung, and kidney.

       In humans, the retinoid delivery pathway to tissues involves primarily retinol bound to retinol‐binding protein; chylomicrons, very low density lipoprotein, low density lipoprotein, and albumin also provide transport.

       Adverse effects in humans include increased bone turnover by suppressing osteoblast activity and stimulating osteoclast formation. This can lead to hypercalcemia, osteoporosis, pathologic fractures, altered skeletal development in children, and skeletal pain.

       Vitamin A is fat soluble and high levels can affect metabolism of other fat‐soluble vitamins (D, E, K); with the effects on vitamin D contributing to the aforementioned bone pathology, although stimulation of bone resorption by vitamin A is reported independent of effects on vitamin D.

       Vitamin A can have a toxic effect on mitochondrial function and is reported to cause hypothyroidism in mice.

       First time owner of reptiles/species and young animals.

       Owner using OTC vitamin A drops, OTC multivitamin with vitamin A in formulation other than beta carotene, using cod liver oil or feeding liver to a carnivorous/omnivorous animal.

       Occasional issues with extruded diets with inadvertent toxic levels of non‐beta carotene vitamin A.

       Patients present with vague signs such as anorexia, dehydration, lethargy.

       Usually has a dermatological component including: dysecdysis, epidermal flakiness, ulceration, and sloughing.

       Bilateral epiphora and periorbital edema may be noted.

       Ulcerative stomatitis can be seen.

       Secondary bacterial and fungal infections can occur.

       Based on pathophysiology, suspect that metabolic bone disease may have interplay with hypervitaminosis A.

       Juvenile animal

       Reproductively active female

       Liver disease

       Hypovitaminosis A

       Infection

       Hepatic or renal disease

       UVB or thermal burns

       Poor overall husbandry or diet

       Improper conspecific arrangement

       Metabolic bone disease

       Liver biopsy for histopathology and testing vitamin A levels (need normal values for the species).

       Presumptive diagnosis based upon history and clinical presentation.

       Hepatic fibrosis

       Osteoporosis

       Decreased or abnormal bony growth in juvenile animals.

       Epidermal ulceration