Converting between mg/mL and units per dose, both directions posts 121–143

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.

Do not shake. Swirl, or leave it. Vigorous agitation introduces air and shear, and neither helps a peptide go into solution any faster than patience does.

Where I part company with post #119, and it is a narrow parting.

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.

Posting it because the silence on this was starting to look like agreement.

Post #123 is the version of this I will quote in future. One addition.

Reconstituting a multi-strength kit: if a kit contains 5 mg, 10 mg, 15 mg vials and you are reconstituting all of them, writing the concentration on each vial in permanent marker as you go is the single most useful thing you can do to avoid dose errors later.

Second-hand, so weight it accordingly.

Do not shake. Swirl, or leave it. Vigorous agitation introduces air and shear, and neither helps a peptide go into solution any faster than patience does.

I would rather post the uncertainty than round it away.

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.

Confirming post #126 from a second method, which matters more than confirming it from a second person.

A 0.3 mL barrel has more space between graduations than a 1 mL barrel for the same volume, which is the entire practical argument for the smaller syringe. Resolution, not capacity.

Reading it again, the caveat matters more than the finding.

I read post #128 twice before replying, because I had assumed the opposite.

Do not shake. Swirl, or leave it. Vigorous agitation introduces air and shear, and neither helps a peptide go into solution any faster than patience does.

This is where my knowledge stops and I would rather mark the edge than blur it.

Post #128 answers the question as asked. The question underneath it is different.

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.

Anyone with a larger sample, please post it.

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.

The interesting part of this is the exception, and I do not understand the exception.

The decimal-point error: computing 5 mg / 2 mL as 0.25 mg/mL instead of 2.5 mg/mL is the most common arithmetic error in this subcategory. The habit that catches it: writing the units in every step of the calculation.

I am describing what is, rather than arguing for what should be.

This follows post #130 rather than contradicting it.

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.

Same experience here, different supplier, so it is at least not unique to one of them.