Checking someone else's arithmetic: a worked example thread

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.

A 10 mg vial reconstituted three different ways: 1 mL diluent gives 10 mg/mL, 2 mL gives 5 mg/mL, 4 mL gives roughly 2.5 mg/mL. The arithmetic is the same; the concentration determines which syringe graduations are legible.

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.

That holds under the stated conditions and I have stated them.

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.

Speaking for myself and not for anyone else who has posted here.

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.

Old habit: I write down the expected answer before I calculate it.

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.

Confirming post #54 from a second method, which matters more than confirming it from a second person.

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 read post #62 twice before replying, because I had assumed the opposite.

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.

Two people can read the same figure differently here and both be reasonable.

Post #72 is right about the mechanism and I think understates the practical bit.

Worked example, since the arithmetic is the whole question. Five milligrams into one millilitre is 5 mg/mL. A 0.25 mg dose is 0.05 mL, which is five units on a U-100 syringe. Check that against your own numbers rather than taking mine.