How many treatment days one vial provides
This explains how to estimate how many days a 10 ml vial will last from weight, mg/kg, and strength.
Formula
Divide the required mg per day by the formulation strength in mg/ml to get the daily liquid volume. Divide the vial volume by that daily volume to estimate the number of days.
Rounding and losses
In practice, residue in the equipment and measurement error may mean the actual number of days differs from the calculation.
Recalculate regularly
If the cat's weight changes during treatment, share the new weight with the veterinarian and confirm the required amount.