Why do we use isophane insulin instead of insulin?

Rarely nowadays: B"sd In fact, most endocrinologists rarely prescribe it (brand name Humulin N) - in fact it is a recombinant human insulin made in bacteria. Mostly, we now use longer acting modified insulins replacing NPH. We also rarely use regular human insulin for rapid action since there are 3 modified (analoges) that have a quicker onset and and shorter duration to better cover meals. But NPH is cheaper.