An in-vitro test for the duration of action of insulin suspensions.

A method is described which measures the prolongation effects of commercial insulin suspensions by monitoring the rate of solution of an insulin suspension into a phosphate buffer, pH 7.4, at 37 degrees C. The method can rapidly categorize an insulin into the clinical classifications of either fast, intermediate or slow acting. It offers advantages of speed and sensitivity over the British Pharmacopoeial test for prolongation of insulin effect in fasted animals. Large differences between the dissolution rates of commercial samples of isophane insulin were observed which suggested a lack of bioequivalence.