Since insulin must be used parenterally and since injections once daily seem to be the inevitable minimum because of normal eating and sleeping habits, it should be possible to select an ideal insulin for routine treatment of diabetes mellitus.
Protamine zinc insulin is too slow and prolonged in action for best control of severe diabetes. When large doses are used, insulin shock is prone to occur during fasting, especially at night.1 In severe diabetes heavy glycosuria occurs after meals.2 Supplementary injection of ordinary insulin helps to correct such faults, but even so control in many cases remains imperfect and the penalty of multiple injections is imposed.3
Mild diabetes is easily controlled with protamine zinc insulin injected once daily.4 This does not imply that it is an ideal insulin, because almost any type of depot insulin will do just as well in small doses for mild diabetes.
COLWELL AR. NATURE AND TIME ACTION OF MODIFICATIONS OF PROTAMINE ZINC INSULIN. Arch Intern Med (Chic). 1944;74(5):331–345. doi:10.1001/archinte.1944.00210230023002