Five checks before every injection

Almost every dosing error with a compounded vial is one of five things. Each has a one-line check. Do all five, in order, every time, out loud if it helps.

1. Is this the right day and the right step?

Look at your schedule or calendar. Confirm today is an injection day and which step you are on. If today is a step-change day, confirm your prescriber actually agreed to the increase. A highlighted row on a schedule is a reminder, not a prescription.

2. What is the concentration on this vial?

Read the label on the vial in your hand. Write the concentration as mg/mL, dividing totals if the label gives them. Compare with the vial you used last time. If it is different, every units figure you remember is now wrong, and you recompute before doing anything else. The label guide covers the formats.

3. What is the dose in milligrams, and what volume is that?

Take the milligram dose from the prescription for the current step. Volume in mL = mg / (mg/mL). Units = mL x 100. Run it through the converter and confirm the mg line matches the prescription. If the volume is near or above 1 mL, or under 0.02 mL, stop; something is wrong with an input.

4. Is this the right syringe, and does the number land on a mark?

Confirm the barrel says U-100. Confirm the capacity is above the volume with some headroom. Confirm the units figure lands on or near a graduation, and that the rounding error is small relative to the dose; the converter's syringe table shows this. The syringe guide explains why a 17-unit dose belongs in a 0.3 or 0.5 mL syringe, not a 1 mL one.

5. Does the pharmacy's own instruction agree?

If the label or the instructions carry a units figure, it must equal yours. If it does not, one of you is working from a different concentration or a different dose. Do not proceed on either number. Call the pharmacy with the vial in hand and read them the lot number.

If a check fails

Stop, and do not inject. Do not take a partial dose "to be safe", and do not take a second injection later to make up a suspected shortfall. Call your pharmacist or prescriber. If you believe you have already injected the wrong amount, call them now, or the poison control line in your country, and tell them the concentration, the volume and the time. The FDA's summary of adverse event reports for compounded semaglutide describes exactly these errors, which is a reason to treat the routine as non-negotiable rather than as paranoia.

Why a routine and not a memory

Concentrations change between fills. Steps change every four weeks during titration. Syringes get restocked in a different size. Each of those is a small change that makes last month's correct number this month's wrong one. A routine that starts from the vial and the prescription every time is immune to all of them. The calculators on this site are built the same way: nothing is stored, nothing is pre-filled, and the number you need comes from the label and the prescription, every time.