Lantus can be mixed with other insulins.
The package insert for Lantus recommends not mixing Lantus with other insulins.
There's concern the acidity of Lantus will cause other insulins to precipitate...possibly reducing the effectiveness of both insulins. An animal study found that mixing Lantus delays onset of action and slightly lowers the bioavailability of regular insulin.
But recent research shows that mixing Lantus with Humalog or NovoLog does NOT compromise long-term glycemic control. Children who mixed Lantus with Humalog or NovoLog in the same syringe did not differ in 6 month HbA1c levels compared to those who used separate injections. And another study detected no differences in overnight, preprandial, or postprandial glucose levels when patients combined the insulins.