Intravenous chlormethiazole- haemolysis with concentrated solutions

Since the current clinical concentration of chlormethiazole solutions (0.8%) may require the infusion of large volumes of fluid, it was decided to examine the effects on haemolysis of infusing higher concentrations of chlormethiazole into a central vein. Approximately one gram of chlormethiazole was infused into the inferior vena cavae of six anaesthetised greyhounds over each half hour using, successively, 0.8%, 1.2%, 2%, 5%, 10%, and 20% solutions of chlormethiazole. Free plasma haemoglobin levels were measured at five minute intervals, and blood chlormethiazole levels at 15 minute intervals. A rapidly progressive haemolysis occurred when the 5 or 10% solutions were infused. In a further four greyhounds, one gram of chlormethiazole was infused over each half hour using a 0.8% solution, whilst progressively hyperosmolar dextrose solutions were infused at the same rates in succeeding half hours as the concentrated chlormethiazole solutions had been infused in the first six dogs. No haemolysis occurred in these control animals. Chlormethiazole blood levels were similar in each group. Loss of chlormethiazole into the infusion tubing was examined and found to be 20% for the 0.8% solution, and 10% for the 1.2% solution, but was insignificant with the other subsequently infused concentrations of chlormethiazole. It is concluded that rapid progressive haemolysis occurs in association with the infusion of chlormethiazole solutions when concentrations of greater than 5 or 10% are infused into the inferior vena cavae of anaesthetised greyhounds.