This is a 50% insulin lispro, 50% insulin lispro protamine suspension mixed, intermediate-acting Eli Lilly analog insulin[1]. Humalog 50 [2], AKA Humalog 50/50, has a 50% fraction of crystals which consist of a combination of insulin lispro and protamine for suspension.
A study of dogs from 1993-1994 using various fractions of Humalog mixes against human NPH/isophane insulin found only minor differences in the use of Humalog Mix as opposed to NPH/isophane insulin[3].