Needle changes between doses on a reusable pen

Storage instructions for a pen typically differ before and after first use, and the in-use period is the one people miss. It is on the carton.

That much is documented. The rest is how I have interpreted it.

Comparing cost per milligram between a pen and a vial ignores wastage, dead volume and the number of doses actually obtainable. Cost per delivered dose at your dose is the comparison that survives.

Nothing here is medical advice, and pen technique is the single easiest thing to have demonstrated in person rather than learned from a description.

Narrowing post #17, because the general version has more than one answer.

Storage after first use: most pens can be stored at room temperature after first use, even if unrefrigerated, for a limited time (often 28 days). Check your specific pen's labelling.

A single observation, in a thread that deserves better than single observations.

Understood. Thank you for being specific about the limits of it.

A pen that will not dial to the intended dose is usually telling you the cartridge does not contain enough for it. That is a designed behaviour rather than a fault.