Topic summary

Revisiting: Completing a dose with a second syringe, and the dead-volume arithmetic

Practice › Administration subcutaneous injection aseptic technique needle gauge & length injection site reaction Closed

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e.dalgleishTL3Regular22 Nov 2024#1

Revisiting: Completing a dose with a second syringe, and the dead-volume arithmetic Writing it up because I had to work it out twice and would rather nobody else did.

I have read the maintained page on this and I still have a gap, so I am asking rather than guessing.

Context: tirzepatide, 23 weeks in, currently at a dose I reached by the standard four-week steps. Everything below is my own record rather than anything a clinician told me.

The specific question is the one in the title. What I have already checked: the labelling summary on the relevant documentation page, the two most-linked topics in this subcategory, and my own notes from the last 6 weeks. What I could not find is whether the answer changes at higher doses or whether it is the same arithmetic throughout.

If the answer is "it depends", I would rather know what it depends on than be given a number.

58 likes 20mo

m.ivaturiTL219 Feb 2025#6

If you are new and reading this thread for the answer to Completing a dose: the answer is conditional, the conditions are in the third reply, and the rest of the thread is worth skipping.

22 likes 17mo

c.niemelTL3Regular11 Apr 2025 · edited#10

Narrowing post #9, because the general version has more than one answer.

A site rotation scheme that actually works: abdomen, outer thigh, back of arm, outer hip. Rotate through them in order, move a minimum 2 cm between consecutive sites, note the site with each dose. If a local reaction appears you have the history. If you rotate properly you will not get lipohypertrophy from overuse of one area.

I would hold that lightly until someone with a larger sample weighs in.

30 likes 16mo

c.vermeulenTL28 Jun 2025#15

Leak-back after withdrawal: a small amount of liquid on the skin after withdrawal is ordinary. Whether you lost a "meaningful" dose depends on concentration and your target dose, but some leak-back is universal and does not need to be treated as an error.

24 likes 14mo

preregisteredTL3Research methods31 Jul 2025#20

If you have to inject at a different time of day than usual, that is a much smaller perturbation than it feels for a weekly compound with a week-long half-life.

18 likes 12mo

Read the full topic (21 posts)

This topic was referenced in

Pinch or no pinch, and how needle length changes the answer — the long versionPractice › Administration · 79 replies

This topic was closed 90 days after the last reply. Closing is automatic for quiet topics so that a settled answer does not collect new questions underneath it. If you have a follow-up, open a new topic and link back to this one — that keeps both readable and gives your question its own title.

Moved from Reconstitution by dr_okonkwo. Category placement is not obvious from outside and getting it wrong is expected. This topic will get better answers here. The move is recorded in the public log citing R7.

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