VPT 421: Veterinary Toxicology (2+0)

CLINICAL SIGNS

• Signs of phenothiazine toxicosis in the horse include dullness, weakness, anorexia, and possibly oliguria, colic, constipation, fever and rapid pulse.
• Hemolytic effects include icterus, anemia and hemoglobinuria.
• Photosensitization may accompany administration of phenothiazine when animals are subsequently exposed to bright sunlight.
• Photosensitization occurs especially in calves but may also occur in goats, sheep and fowl but not horses.
• When the dose of phenothiazine is sufficiently high, not all the phenothiazine sulfoxide is converted to leucophenothiazine and leucothionol by the liver.
• Calves are apparently less adept at this conversion than older cattle or sheep.
• A portion of the phenothiazine sulfoxide diffuses into the aqueous humor.
• On exposure to sunlight, photochemical reaction results in keratitis and often corneal ulceration within 36 hours.
• Non-pigmented areas of the skin may be reddened, especially commonly affected are the ears, muzzle and other parts of the face.
• Shaking of the head, rubbing of the ears and other signs of irritation may be seen.
• A slight increase in abortion in ewes given phenothiazine at 3 weeks before the end of gestation has been reported.
• Generally, phenothiazine is contraindicated only during the last month of gestation.
• Phenothiazine discolored milk can generally be regarded as safe for feeding other animals.
• Permanent staining of wool or haircoat may result from phenothiazine excreted in the urine or from spilling the drench on the animal.