Comparative effects of hyperosmolar urea administered by intra-amniotic, intravenous, and intraperitoneal routes in rhesus monkeys.

Hypertonic urea solutions (58 per cent weight/volume) were injected rapidly into ten anesthetized rhesus monkeys at a dose of approximately 2 Gm. per kilogram by the intravenous, intraperitoneal, or intra-amniotic routes. An additional monkey received an intra-amniotic dose of 12.5 Gm. per kilogram. A tracer dose 14C-urea was included for measuring absorption and elimination. The following parameters were monitored before and for four hours after urea injection: arterial and cerebrospinal fluid pressures, heart and respiration rates, urine flow, and urea clearance. Serum electolytes, hematocrit and white count, and cumulative urea excretion were measured for one week. Monkeys were observed for three to six months after injection. At doses up to approximately twice the human dose (on a body weight basis) there were no urea-related deaths and no serious side effects noted in any of the experiments. These results support the suggestion that urea is a relatively safe hyperosmolar agent for inducing midtrimester abortions, especially with regard to inadvertent systemic injection.