Tirzepatide: the published schedule and the vial mass

The tirzepatide is a single chain that activates two receptors: the GIP receptor and the GLP-1 receptor. Both are incretins, released after a meal. Activating them together is not "two semaglutides". The profile, dose and ceiling are not the same.

Mounjaro and Zepbound are the names of the Lilly medicines, in pens. The catalogue vial is a lyophilizate. A 60, 80 or 100 mg vial is not a pen loaded at that dose: it is a mass of powder.

The escalation, four weeks per step

SURMOUNT-1 (Jastreboff et al., New England Journal of Medicine, 2022) and the label start at 2.5 mg and go up by 2.5 mg every four weeks. The published ceiling is 15 mg once a week. You do not start at 15 mg, and you do not exceed this ceiling because the vial is bigger.

• Weeks 1 to 4: 2,5 mg
• Weeks 5 to 8: 5 mg
• Weeks 9 to 12: 7,5 mg
• Weeks 13 to 16: 10 mg
• Weeks 17 to 20: 12,5 mg
• From week 21: 15 mg

Each step lasts four weeks, on the same day. The 2.5 mg step is a start-up: in the trials, it is not the step studied for effect; it prepares the next ones. The page protocols reproduces this table and the dilutions.

Which vial for which volume

The useful step is to obtain a concentration close to 10 mg/mL, so that 2.5 mg is 0.25 mL.

• 10 mg in 1 mL, 20 mg in 2 mL, 30 mg in 3 mL: 10 mg/mL. 2.5 mg = 0.25 mL. 5 mg = 0.50 mL. 10 mg = 1 mL.
• 40 mg, 60 mg, 80 mg and 100 mg are reconstituted in 3 mL, a common vial volume. The concentration rises: 13.3 mg/mL, 20 mg/mL, 26.7 mg/mL, 33.3 mg/mL. The volume to draw for 2.5 mg becomes smaller. It is calculated; you do not "take the vial".

Holding the step

Same day every week. A forgotten dose is not made up by adding two steps. Stay on the current step. If the digestive effects of the step are too marked, the reflex in the trials is to stay four more weeks at the previous dose, not to skip the next one.

Powder and solution are kept between 2 and 8 °C, away from light. The reconstitution date is written on the label. The shelf life used on the catalogue pages after reconstitution is up to 28 to 30 days. A 100 mg vial reconstituted in 3 mL does not last longer because it is more concentrated: cold and the date count in the same way.

In the catalogue, from the 10 mg vial to the vial 100 mg. To compare the molecule with semaglutide and R3TA: the guide to the three agonists.

What the vial figure does not say

Going from 10 mg of powder to 100 mg of powder does not change the schedule. It changes the number of draws that can be made from the same solution, and the precision of the mark on the syringe. A very high concentration makes a 2.5 mg step hard to measure. That is why small vials are reconstituted more concentrated only when the volume stays readable, and large ones stay in 3 mL with a calculation, not an improvised dose.