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

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FP
f.piresTL2 Moderator25 Jan 2026#1

Posting this under the heading it deserves: Completing a dose with a second syringe, and the dead-volume arithmetic Everything below is what sits behind that.

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

Context: tirzepatide, 19 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 10 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.

33 likes 6mo
RM
r.marsdenTL3Regular31 Jan 2026#2
Community wiki post. Any member at trust level 3 or above can edit this post; every edit is recorded. Last edited by r.venkatesan on 14 Feb 2026.
  • 16 Apr 2026 — coldchain_liu: Removed a claim that the cited source did not support.
  • 14 Feb 2026 — r.venkatesan: Replaced an unsourced figure with the published one and cited it.
Editors: coldchain_liu, r.venkatesan

Angle of injection: 90 degrees into pinched tissue ensures subcutaneous placement. It is not always necessary and shallower angles can work, but 90 degrees into a small pinch is the safest technique to learn first.

0 likes 6mo
NS
n.serranoTL2 Moderator5 Feb 2026#3
r.marsden, post #2: Angle of injection: 90 degrees into pinched tissue ensures subcutaneous placement. It is not always necessary and shallower angles can work, but 90 degrees into a small pinch is the safest technique to learn first. Go to post

Air bubbles in a subcutaneous injection: the honest risk assessment is low. Tiny air bubbles in subcutaneous tissue do not behave like an air embolism in a blood vessel. A few air bubbles are not a reason to restart the entire injection.

1 like in reply to #2 6mo
L
LeitermanTL3Regular9 Feb 2026 · edited#4

I read post #2 twice before replying, because I had assumed the opposite.

Cold solution and stinging: warming the vial in your hands for a minute before injection reduces the stinging sensation substantially. This is the simplest thing to try if injections are uncomfortable.

7 likes 6mo
MR
m.ramosTL2 Moderator12 Feb 2026#5

Bleeding at the injection site: normal and usually minimal. A little blood at the needle site after withdrawal is not a reason to assume you lost a significant dose. The needle passed through tissue and there is a small amount of bleeding in the tract.

25 likes 5mo
ST
sterile_tableTL3Regular16 Feb 2026#6

Having read the exchange above, I think I was wrong earlier in this topic and I want to say so plainly rather than quietly editing.

The correction was fair and I had been repeating something I had not checked carefully enough.

0 likes 5mo
YE
y.eriksenTL2 Moderator19 Feb 2026#7
Leiterman, post #4: I read post #2 twice before replying, because I had assumed the opposite. Cold solution and stinging: warming the vial in your hands for a minute before injection reduces the stinging sensation substantially. This is the simplest thing to try if injections are uncomfortable. Go to post

Picking up post #4: that is the part I would want checked first.

Injecting into an area that has become firm: lipohypertrophy — thickened fatty tissue from repeated injection in one area — changes local tissue absorption. Avoid injecting into areas that are noticeably firm or lumpy and allow those areas to recover for at least a few months.

3 likes in reply to #4 5mo
P
PSundbergTL2Member22 Feb 2026#8

Coming back to post #6, because the follow-up matters more than the original answer.

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.

11 likes 5mo
AA
a.adeyemiTL2 Moderator25 Feb 2026 · edited#9

Injection discomfort: comes from needle gauge (finer = less discomfort), volume (smaller = less discomfort), temperature (room temperature or warmed is less uncomfortable than cold), and technique (smooth, purposeful injection is less uncomfortable than hesitant). All four are under your control.

33 likes 5mo
RH
revision_historyTL3Wiki editor1 Mar 2026#10
a.adeyemi, post #9: Injection discomfort: comes from needle gauge (finer = less discomfort), volume (smaller = less discomfort), temperature (room temperature or warmed is less uncomfortable than cold), and technique (smooth, purposeful injection is less uncomfortable than hesitant). All four are under your control. Go to post

Worth separating two things that post #6 runs together.

Drawing up with one needle and injecting with another: a reasonable practice if you have extra needles. Fresh needle for injection reduces tissue drag and can decrease discomfort. Not necessary, but not harmful either.

0 likes in reply to #9 5mo
P
PSundbergTL2Member3 Mar 2026#11
sterile_table, post #6: Having read the exchange above, I think I was wrong earlier in this topic and I want to say so plainly rather than quietly editing. The correction was fair and I had been repeating something I had not checked carefully enough. Go to post

I read post #9 twice before replying, because I had assumed the opposite.

A genuinely late dose: the labelling generally says that if the next dose is more than a couple of days away, take it as soon as you notice. If the next dose is close, skip it and resume the schedule. The reasoning follows from the long half-life; you are perturbing a slowly moving average.

17 likes in reply to #6 5mo
YE
y.eriksenTL2 Moderator6 Mar 2026#12

Pinch or no pinch: the decision depends on needle length and on your own anatomy. A longer needle (8 mm and up) reaches subcutaneous tissue easily without a pinch. A shorter needle (4-6 mm) is safer with a gentle pinch. The pinch size matters less than people think; the injection angle matters more.

7 likes 5mo
ST
sterile_tableTL39 Mar 2026#13
MR
m.ramosTL2 Moderator12 Mar 2026 · edited#14
y.eriksen, post #12: Pinch or no pinch: the decision depends on needle length and on your own anatomy. A longer needle (8 mm and up) reaches subcutaneous tissue easily without a pinch. A shorter needle (4-6 mm) is safer with a gentle pinch. The pinch size matters less than people think; the injection angle matters more. Go to post

post #13 is right about the mechanism and I think understates the practical bit.

Air bubbles in a subcutaneous injection: the honest risk assessment is low. Tiny air bubbles in subcutaneous tissue do not behave like an air embolism in a blood vessel. A few air bubbles are not a reason to restart the entire injection.

0 likes in reply to #12 5mo
CR
curious_readerTL1Member15 Mar 2026#15

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.

23 likes 4mo
JI
j.ivaturiTL2 Moderator17 Mar 2026#16

Bleeding at the injection site: normal and usually minimal. A little blood at the needle site after withdrawal is not a reason to assume you lost a significant dose. The needle passed through tissue and there is a small amount of bleeding in the tract.

11 likes 4mo
RH
revision_historyTL3Wiki editor20 Mar 2026#17

On post #13 — agreed on the reasoning, with one qualification.

Two things before anyone answers the substance.

First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.

3 likes 4mo
AA
a.adeyemiTL2 Moderator23 Mar 2026 · edited#18
revision_history, post #17: On post #13 — agreed on the reasoning, with one qualification. Two things before anyone answers the substance. First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound. Go to post

post #17 answers the question as asked. The question underneath it is different.

Injecting into an area that has become firm: lipohypertrophy — thickened fatty tissue from repeated injection in one area — changes local tissue absorption. Avoid injecting into areas that are noticeably firm or lumpy and allow those areas to recover for at least a few months.

0 likes in reply to #17 4mo
JH
j.habermannTL3Regular25 Mar 2026#19

Two things before anyone answers the substance.

First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.

31 likes 4mo
KO
k.okaforTL2 Moderator28 Mar 2026#20

This follows post #17 rather than contradicting it.

Drawing up with one needle and injecting with another: a reasonable practice if you have extra needles. Fresh needle for injection reduces tissue drag and can decrease discomfort. Not necessary, but not harmful either.

16 likes 4mo
CI
c.inglethorpeTL3Regular30 Mar 2026#21

This follows post #18 rather than contradicting it.

Cold solution and stinging: warming the vial in your hands for a minute before injection reduces the stinging sensation substantially. This is the simplest thing to try if injections are uncomfortable.

5 likes 4mo
FC
f.chowdhuryTL2 Moderator2 Apr 2026#22
c.inglethorpe, post #21: This follows post #18 rather than contradicting it. Cold solution and stinging: warming the vial in your hands for a minute before injection reduces the stinging sensation substantially. This is the simplest thing to try if injections are uncomfortable. Go to post

I read post #20 twice before replying, because I had assumed the opposite.

Injection discomfort: comes from needle gauge (finer = less discomfort), volume (smaller = less discomfort), temperature (room temperature or warmed is less uncomfortable than cold), and technique (smooth, purposeful injection is less uncomfortable than hesitant). All four are under your control.

15 likes in reply to #21 4mo
C
CSagredoTL3Regular4 Apr 2026 · edited#23

Thank you for the correction. I have edited my earlier post with a note rather than silently, so the thread still makes sense to read. The error was mine and it was the kind that comes from remembering a figure instead of looking it up.

0 likes 4mo
RM
r.molnarTL2 Moderator7 Apr 2026#24

A genuinely late dose: the labelling generally says that if the next dose is more than a couple of days away, take it as soon as you notice. If the next dose is close, skip it and resume the schedule. The reasoning follows from the long half-life; you are perturbing a slowly moving average.

0 likes 4mo
ME
m.eriksenTL2 Moderator9 Apr 2026#25

Picking up post #22: that is the part I would want checked first.

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.

9 likes 4mo
ME
m.ekstromTL2 Moderator12 Apr 2026#26
n.serrano, post #3: Air bubbles in a subcutaneous injection: the honest risk assessment is low. Tiny air bubbles in subcutaneous tissue do not behave like an air embolism in a blood vessel. A few air bubbles are not a reason to restart the entire injection. Go to post

Angle of injection: 90 degrees into pinched tissue ensures subcutaneous placement. It is not always necessary and shallower angles can work, but 90 degrees into a small pinch is the safest technique to learn first.

21 likes in reply to #3 4mo
T
ThibodeauTL3Regular14 Apr 2026#27
PSundberg, post #11: I read post #9 twice before replying, because I had assumed the opposite. A genuinely late dose: the labelling generally says that if the next dose is more than a couple of days away, take it as soon as you notice. If the next dose is close, skip it and resume the schedule. The reasoning follows from the long half-life; you are… Go to post

Pinch or no pinch: the decision depends on needle length and on your own anatomy. A longer needle (8 mm and up) reaches subcutaneous tissue easily without a pinch. A shorter needle (4-6 mm) is safer with a gentle pinch. The pinch size matters less than people think; the injection angle matters more.

0 likes in reply to #11 3mo
HA
h.amankwahTL2 Moderator16 Apr 2026#28

Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive.

2 likes 3mo
I
IMainwaringTL3Regular19 Apr 2026#29
Thibodeau, post #27: Pinch or no pinch: the decision depends on needle length and on your own anatomy. A longer needle (8 mm and up) reaches subcutaneous tissue easily without a pinch. A shorter needle (4-6 mm) is safer with a gentle pinch. The pinch size matters less than people think; the injection angle matters more. Go to post

Thank you for the correction. I have edited my earlier post with a note rather than silently, so the thread still makes sense to read. The error was mine and it was the kind that comes from remembering a figure instead of looking it up.

1 like in reply to #27 3mo
LL
l.lundgrenTL2 Moderator21 Apr 2026#30

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.

6 likes 3mo