Asking directly, because I could not find a straight answer: Pen mechanics when the cartridge is nearly empty — does this still hold?
Pen mechanics — I have the observation and I do not trust my interpretation of it, so I am posting the observation and holding the interpretation back.
Numbers, method and the conditions under which they were collected are below. Interpret them however they warrant.
Post #2 answers the question as asked. The question underneath it is different.
Priming exists because the needle and the cartridge path contain air after a needle change. Skipping it means the first fraction of the dose is not liquid.
That much is documented. The rest is how I have interpreted it.
I read the opening post twice before replying, because I had assumed the opposite.
Dose counters: pens show the remaining number of doses. When the counter reaches zero, the pen is empty and cannot deliver more. Noting the counter before injection prevents running out unexpectedly.
Picking up post #2: that is the part I would want checked first.
The instruction leaflet for a licensed pen is a genuinely good technical document and is almost never read past the first page. It answers most of what gets asked here.
A pen taken straight from the refrigerator is uncomfortable to inject for the same reason a cold syringe is. Room temperature for a short while first is the standard advice.
Adding the measurement that post #6 says would settle it.
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.
Post #9 describes the usual case. This is about the unusual one.
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.
I would put the burden of proof on the interesting explanation, not the dull one.
An update on my earlier Pen mechanics post: the pattern held for another six weeks and then stopped, which I did not predict and cannot explain.
This follows post #11 rather than contradicting it.
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.
Written from notes rather than memory, which is why the numbers are specific.
The click count on a dialled pen is a mechanical property of that pen and is not a universal unit. Counting clicks across two different devices is not a conversion.
If that reads as pedantic, it is, and it has saved me twice.
Thank you — that answers what I came here to find out.
Picking up post #15: that is the part I would want checked first.
Disposal of a used pen is a sharps question even where the needle is retracted, and local rules vary more than people expect.
The evidence for this is thinner than the way I have phrased it suggests.
Answering the question post #15 raises rather than the one it answers.
A pen delivers a fixed or dialled dose from a cartridge and is a metering device rather than simply a covered syringe. That is why dose changes are constrained to whatever the mechanism supports.
Not disagreeing with anyone above, just adding the bit I keep having to look up.
The arithmetic in post #19 is right; the assumption feeding it is the part to check.
Air in a cartridge behaves differently from air in a syringe because the mechanism displaces a fixed volume regardless. That is what priming addresses.
It is worth stating the boring hypothesis before the interesting one.
Pen mechanics: most pens are dial-and-inject devices where you dial the dose on the pen and push the button to inject. Understanding your specific pen's mechanism prevents dose errors.
If anyone has run this properly I would rather read that than my own guess.
Some pens indicate remaining doses and some do not, and reading the residual volume by eye through a window is unreliable at the end of a cartridge.
The arithmetic in post #20 is right; the assumption feeding it is the part to check.
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.
That is the shape of it. The detail is where I would expect to be corrected.
No disagreement from me. Posting only so the question does not look ignored.
Confirming post #23 from a second method, which matters more than confirming it from a second person.
Needle installation: some pens require a fresh needle for each injection; others have a single needle that stays attached. Check the design of your pen.
Noting that the question and the thing people usually mean by it are different.
Reusability: some pens are single-use (throw away after one injection). Others can be reused until empty. Confirm which type you have. Reusing a single-use pen is ineffective because the mechanism does not reset.
Written quickly, so the reasoning may be tighter than the wording.
Travel with a pen raises a cold-chain question and a documentation question. The second is the one people forget until an airport.
That is a fair summary of where the discussion has got to.
Post #26 and I disagree about the size of the effect, not about the direction.
Pen confusion between compounds: if you are using multiple pens or alternating pens, confirming you have the correct pen before injection prevents administration errors. Check the label every time.
I would treat that as a working assumption and revisit it.