Planning pack sizes for a study that runs for weeks

Most shortfalls in a long study are not caused by the material running out on the last day. They come from planning the first week as if the rest of the study did not exist. Working backwards from the schedule removes most of that risk.

Start from the run calendar

Write down every planned run with its date, the number of samples it needs and the number of replicates. Add one extra run per month for repeats, because repeats are normally needed and rarely scheduled. The total is the amount of material the study consumes, not the amount your protocol mentions on the first page.

Choose the fewest vials that cover the total

• Fewer openings reduce handling steps and the number of records to keep
• Matching lots across the whole study remove one source of variation
• Keep a small reserve unopened so a failed run does not stop the schedule

A multi-vial kit suits a study with several identical arms, because every arm draws from the same lot. A single larger vial suits a single arm that runs for a long period. Mixing the two is common and works well if the lot numbers are recorded for each vial.

Write the plan down before the first order

A one-page allocation table, listing vial, lot number, planned use and date opened, is enough for most studies. It is also the document a reviewer will ask for first, so it is worth keeping current from day one.