VPT 421: Veterinary Toxicology (2+0)

PRIMARY PHOTOSENSITIZATION OR TYPE I

• Primary photosensitization occurs when the photodynamic agent is absorbed either through the skin or from the GI tract unchanged, reaching the skin in its native form.
• Examples of primary photosensitizers are hypericin (from Hypericum perforatum [St. John’s wort]).
• Plants in the families Umbelliferae and Rutaceae contain photoactive furocoumarins, which cause photosensitization in livestock and poultry.
• Ammi majus (Bishop’s weed) and Cymopterus watsonii (spring parsley) have produced photosensitization in cattle and sheep, respectively.
• Species of Trifolium , Medicago (clovers and alfalfa), Erodium , Polygonum , and Brassica have been incriminated as primary photosensitizers.
• Many other plants have been suspected, but the toxins responsible have not been identified.
• Additionally, some coal tar derivatives, phenothiazine, sulfonamides and tetracyclines have induced primary photosensitivity.