Chronic toxicity of DMSO in primates

Oral administration or dermal application of pharmaceutical grade DMSO has been evaluated in rhesus monkeys (Macaca mulatta) over an 18-month period. Daily doses of 1, 3, or 9 ml/kg body weight of a 90% (vv) aqueous DMSO solution were administered topically or intragastrically in equally divided portions each morning and afternoon. The topical applications covered the entire abdominal area. Control animals were given 9 ml/kg of water by either route. Body weight, blood pressure, heart rate, respiratory rate, body temperature, water consumption, neurologic reflexes, and ophthalmologic characteristics were observed. Electrocardiograms, hematologic studies, and chemical analyses of blood and urine also were done. Gross and histomorphologic examinations were made terminally. Frequent ophthalmoscopic and biomicroscopic examinations of these animals revealed no evidence of the ocular toxicity reported to have been observed in subprimate species. Animals given the highest oral dose of DMSO could not tolerate it and died between weeks 15 and 53 of the study. Histologically, atelectasis and emphysema were the only pathologic changes. Some regurgitation and/or tracheal inspiration of this highly volatile irritating substance might have occurred. No toxicologic or pathologic changes attributable to oral administration of 1 or 3 ml/kg or topical application of 1, 3, or 9 ml/kg of DMSO (90%) were found.