Revisiting: Drawing up with one needle and injecting with another

Revisiting: Drawing up with one needle and injecting with another Writing it up because I had to work it out twice and would rather nobody else did.

Practical question with the units stated, because I have seen how quickly these go wrong without them.

I have a 2 mg vial of tirzepatide and I am working to a 1.0 mg step. My syringes are U-100 insulin syringes, 1.0 mL barrel.

I can do the arithmetic and I have done it twice, getting the same answer both times, but I would like someone to check the reasoning rather than the number — specifically whether I have thought about the residual volume correctly, and whether the graduation I am landing on is one a person can actually read.

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

I disagree with the reply above, and I think the disagreement is substantive rather than terminological.

The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient.

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.

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.

Worth separating two things that the opening post runs together.

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.

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.

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.

This follows post #5 rather than contradicting it.

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.

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.

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.

post #10 is right about the mechanism and I think understates the practical bit.

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.

Worth separating two things that post #8 runs together.

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.

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.

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.