Air in a cartridge behaves differently from air in a syringe because the mechanism displaces a fixed volume regardless. That is what priming addresses.
Posted with less confidence than the sentence structure implies.
2 likes 7mo
Devices · Pens & autoinjectors · continued
Pen mechanics when the cartridge is nearly empty — does this still hold? posts 31–48
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
a.vermeulen, post #19: 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… Go to post
Confirming post #30 from a second method, which matters more than confirming it from a second person.
Nothing here is medical advice, and pen technique is the single easiest thing to have demonstrated in person rather than learned from a description.
Somebody will have a better source than mine, and I hope they post it.
Collapsed as off-topic by two members at trust level 3 or above
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.
Reading it again, the caveat matters more than the finding.
s.girard, post #11: Nothing here is medical advice, and pen technique is the single easiest thing to have demonstrated in person rather than learned from a description. Go to post
Post #33 describes the usual case. This is about the unusual one.
Holding the pen in place for the stated count after the plunger stops is the manufacturer's answer to leakage at the site. It is on the instruction leaflet and it is the step most often skipped.
I have left out the parts I could not verify.
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.
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That is the distinction I keep failing to hold on to. Written down now.
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p.mwangi, post #39: Reading rather than answering, but this is the post I would point somebody at. Go to post
This follows post #41 rather than contradicting 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.vermeulen, post #6: 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. Go to post
Worth separating two things that post #40 runs together.
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.
Flagging that the sources on this are thinner than the confidence in the thread suggests.
Disposal of a used pen is a sharps question even where the needle is retracted, and local rules vary more than people expect.
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Taking post #46 at face value and following it one step further.
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.
If this contradicts something upthread, the upthread version may well be the better one.
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logbook_erin, post #12: 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. Go to post
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.
The literature is thinner on this than the confidence in the thread implies.
This topic was referenced in
- Storing a pen in use versus a pen unopened — what changed sinceDevices › Pens & autoinjectors · 2 replies
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