A lethal hypervitaminosis A syndrome in young monkeys (Macacus fascicularis) following a single intramuscular dose of a water-miscible preparation containing vitamins A, D2 and E.

Large intramuscular doses of a water-miscible preparation of vitamin A (500,000 I.U. retinyl acetate/ml), vitamin E (50 I.U./ml) and vitamin D2 (50,000 I.U./ml) were administered to young monkeys (Macacus fascicularis) weighing 1-1.8 kg. At vitamin A doses equivalent to 200 mg retinol/kg or higher, early signs of acute toxicity included yawning, apparent drowsiness, nausea and vomiting, head shaking, neck hyperextension, motor hyperactivity and coordination. These immediate signs were first noted 3-35 minutes after injection. Following apparent recovery at 1-2 hrs, longer term signs of toxicity, such as decreased activity, malaise, drowsiness, loss of appetite, loss of weight, and itchiness of the skin, appeared within 1-6 days, depending on the dose. Monkeys receiving the highest lethal doses became progressively weaker, showed labored breathing, lapsed into a coma, lost simple reflexes and then died. Respiratory failure usually preceded the cessation of heart beat. In some monkeys on a lower but lethal dose, death was preceded by generalized convulsive seizures. The time of onset of the first sign and survival time were inversely proportional to the dosage, but in individual monkeys no correlation existed between onset time and survival time. Female monkeys seemed to succumb faster to a lethal dose than male monkeys. All animals receiving the equivalent of 300 mg retinol/kg died. Under the conditions used, the LD50 was estimated to be 168 mg retinol (560 000 I>U.) per body weight.