Liraglutide half-life, time to peak and level curve

What does the label say about liraglutide’s half-life and peak?

Liraglutide, sold as Victoza and Saxenda, clears far faster than the weekly medications. The prescribing information Peptrend cites gives an elimination half-life of approximately 13 hours, puts maximum concentration 8 to 12 hours after a subcutaneous dose, and reports an absolute bioavailability of approximately 55%. The label doses it once a day, and its pharmacokinetics section gives no time to steady state.

The preset stores the half-life as 0.55 days, which is 13.2 hours rather than 13. The half-life stepper widens its step as the value grows, and 0.55 is a value it lands on; the 12-minute difference is small beside the spread between people. The app labels it 13 hours. The 10-hour peak is the middle of the label’s window, and the interval is one day.

What does one dose look like in the model?

One dose climbs for 10 hours and turns over at 59.1% of the logged amount, the lowest peak of the four injection presets. The reason is the ratio: a 10-hour climb is three-quarters of a 13.2-hour half-life, so elimination takes a large share before the peak arrives.

The model also sets a hard limit here. It cannot place a peak later than 1.44 half-lives after the dose, which is about 19 hours at this half-life, and the label’s 12-hour upper end sits inside it. Reading the absorption curve explains where that ceiling comes from.

The day between doses is 1.8 half-lives long, so most of each dose is gone before the next: 38.6% is left when the next daily injection is due.

What happens when daily doses repeat?

Liraglutide settles faster than any other preset. Four to five half-lives is 2.2 to 2.75 days, and three days in, the level just before each injection is within 3% of where it settles. Settled, it swings between 95.1% of one logged dose at its highest and 54.8% just before the next injection.

The settled peak never reaches a full dose’s worth. With about 72% of the level clearing each day, the model builds to only about 1.4 times what a single dose leaves after a day. The label states no time to steady state, so the four-to-five-half-life rule is the only estimate on this page, and it comes from the model. How long a GLP-1 takes to reach steady state sets out that rule.

Where does the model part from the label?

• Bioavailability. The label reports approximately 55% and the model uses 100%, which puts the curve about 1.8 times as high as the label’s figure would. The shape is unchanged.
• Timing. With a 13-hour half-life, the hour of each injection matters: an hour is nearly 8% of a half-life. The app keeps each dose’s time as well as its date, and the model uses both.
• The app’s own chart. On the 1-week and 1-month ranges the app computes the curve every 6 hours. On longer ranges it samples once a day or less often, which is coarser than liraglutide’s own daily rise and fall, so those ranges miss most of the daily peaks and troughs.

Every constant is editable in Settings › Medication, and the app asks before a preset overwrites them.