Thank you for clearing that up for me.
Not to pile on with the questions, but could you answer a related question? What is the rational for some people dosing Lantus in the AM and the PM? E.g. splitting the dose.
Additionally - is the glargine to degludec conversion 1:1? I've read lately that degludec is actually associated with less hypoglycemia than Lantus and want to see about prescirbing this more often.
A) Two reasons:
1) Lantus absorption gets more inconsistent at higher doses. The way that it works is that Lantus after injection microprecipitates and gets absorbed slowly from the subq. A bigger bolus leads to issues where there's a lower surface area, and absorption becomes kinda hinky. Thus, at some point above 50 units/day (ask 10 endocrinologists and you'll get 10 answers between 50 and 80), it's better to split the Lantus into two separate injections. At that point, you either split the Lantus into two injections given at the same time or to one injection given twice a day. Which leads to reason #2:
2) Kinetics of all of our insulins are based on averages. Lantus lasts 24 hours in theory, but there exist people for whom it might only last 20 hours. Or 26 hours. 26 hours is no big deal (a tiny bit of stacking won't kill you), but if you're sensitive, 4 hours without basal can lead to issues. In that case, splitting the dose definitely gives you at least some coverage all day long.
So most people who have it split have it split because of a high dose. A few on a low dose might have it split because they just want to make sure they have consistent coverage. On inpatients, it might also be split because that gives you two opportunities each day to modify the next dose (thus letting you stay more on top of things).
Problem #2 is actually much more pronounced with detemir btw. At low doses, detemir will almost never last a full day and has a bit of a peak besides. I'll almost always use it bid if I'm stuck using the drug.
B) The manufacturer says glargine to degludec conversion is exactly 1:1. In studies, to achieve the same fasting plasma glucose the degludec dose actually tends to be a little bit higher on average. Both of those said though, if the patient is well-controlled previously, whenever I switch from one insulin to another I decrease the dose by 10-20%. Why? Quite simply, people can react differently to different medications. I'd rather underdose them initially and then go up later rather than risk hypoglycemia. I've had plenty of patients who insist they need radically different doses with novolog as compared to humalog, which makes zero sense to me based on any actual evidence I know of, but I just go with it as long as they're doing otherwise OK.
Degludec in SWITCH-1 and SWITCH-2 clearly has less hypoglycemias than glargine. It also definitely has kinetics that last well over a day (leading to no issues with the "might only last 20 hours" problem), can be given at a different time every day without negative effects (thus being better for our patients who have variable schedules), and is available in a U200 formulation that lets you go up to 160 units per dose (as opposed to even U300 glargine which still has a maximum dose of 80 units).
That said, it can't be adjusted as often (takes something like a week to reach steady state), leads to issues if the patient is admitted (never on formulary=awkward period of overlap during the initial admission), tends to have worse coverage (for governmental insurances, commercially insured patients can just get a discount card), and hasn't been around as long.
I've been using more and more degludec recently myself, but it's not for every patient.
