Practice · Reconstitution · continued

Coming back to: Over-dilution: when your dose falls below one readable graduation posts 91–98

Practice › Reconstitution worked example dead volume syringe units bacteriostatic water

This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.

s.karlsen_rphTL3Pharmacist6 Dec 2025#91

b.solberg, post #59: Over-dilution: if your target dose is 0.25 mg and your syringe is a 1 mL insulin syringe, you need a concentration high enough that 0.25 mg fits on the scale. A 0.25 mg/mL solution requires drawing the entire 1 mL syringe — not readable. A 5 mg/mL solution requires drawing 50 μL — also not practical on an insulin syringe. Flagging that… Go to post

Picking up post #90: that is the part I would want checked first.

The arithmetic on Over-dilution is the easy part and it is where the errors are, which is an uncomfortable combination. Show your working and someone will catch it.

4 likes in reply to #59 8mo

n.brobergTL28 Dec 2025 · edited#92

taper_table, post #80: Clear enough that I do not think I have a follow-up, which is unusual. Go to post

Where the Over-dilution discussion usually stalls is that nobody wants to say "I do not know" and everyone is willing to say "it varies". Those are the same sentence with different clothes on.

12 likes in reply to #80 8mo

orbitrap_olaTL3Mass spectrometrist10 Dec 2025#93

Preservative effectiveness is tested against a defined microbial challenge under defined conditions. It is not a licence to treat an entered vial as sterile indefinitely, and no supplier claims otherwise.

Adding this to the thread rather than to the wiki, because I am not confident enough for the wiki.

0 likes 8mo

i.almeidaTL212 Dec 2025#94

I had written a reply contradicting post #92 and deleted it. Here is what survived.

Choosing a concentration on purpose rather than by accident: starting with "I want to draw 0.5 mL per dose" and working backward to the required concentration is more efficient than picking a diluent volume and hoping the math works out. State your target volume, then the required concentration follows.

I would rather say I do not know than round it up to an answer.

0 likes 8mo

c.cardosoTL214 Dec 2025#95

buffer_review, post #52: Coming back to post #48, because the follow-up matters more than the original answer. The confident answers on Over-dilution and the well-sourced answers are not the same answers, which is the most useful thing I have learned reading this category. Go to post

Adding the measurement that post #94 says would settle it.

Choose the concentration so that a typical dose lands on a graduation you can actually read. A dose that falls between two marks on a 1 mL barrel is a dose you will get wrong sooner or later.

I would treat the number as indicative rather than as a measurement.

7 likes in reply to #52 7mo

f.sjobergTL217 Dec 2025#96

Post #92 describes the usual case. This is about the unusual one.

A note on how Over-dilution gets discussed rather than on Over-dilution itself: the confident posts get the replies and the careful ones get ignored, and the careful ones have been right more often.

17 likes 7mo

dr_okonkwoTL4 Moderator19 Dec 2025#97

My position on Over-dilution is current rather than settled. I have revised it once already and I expect to again, so treat it accordingly.

0 likes 7mo

m.perrinTL221 Dec 2025#98

Quietly grateful for the plain phrasing. Not every thread gets that.

1 like 7mo

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