Though it's for human diabetics, here is the technical stuff from
https://www.diabeteshealth.com/lantus-and-levemir-whats-the-difference/:
Lantus and Levemir have a lot in common. Both are basal insulin formulas, which means that they last for a long time in the body and act as background insulin, with a slow feed that mimics the constant low output of insulin produced by a healthy pancreas. Both are insulin analogues, which means that their insulin molecules are analogous to human insulin, but engineered, or recombined, with slight differences that slow their absorption.
Lantus (glargine) is a clear formula made with glargine, a genetically modified form of human insulin, dissolved in a special solution. The modifications make glargine soluble at an acidic pH (about 4pH.), but much less soluble at the neutral pH that’s found in the body. Because glargine is not soluble at a neutral pH, it precipitates out into a form that’s not soluble in subcutaneous fat, and there forms a relatively insoluble depot. From that pool, or depot, of precipitated glargine in the tissues, small amounts slowly move back into solution over time and then to the bloodstream. The acidic nature of Lantus can sometimes cause stinging at the injection site, especially at higher doses.
Levemir is also a clear formula, but it contains dissolved detemir, a different form of genetically modified insulin. Unlike glargine, detemir does not form a precipitate upon injection. Instead, detemir’s action is extended because its altered form makes it stick to itself in the subcutaneous depot (the injection site), so it’s slowly absorbed. Once the detemir molecules dissociate from each other, they readily enter the blood circulation, but there the added fatty acid binds to albumin. More than 98 percent of detemir in the bloodstream is bound to albumin. With the albumin stuck to it, the insulin cannot function. Because it slowly dissociates from the albumin, it is available to the body over an extended period.
