my compounded vial arrived at a different concentration than last month

The title is the argument: my compounded vial arrived at a different concentration than last month. Here is the rest of it.

A 503A pharmacy compounds for an identified patient against a prescription. A 503B outsourcing facility registers with the regulator, may produce without patient-specific prescriptions, and is subject to current good manufacturing practice requirements. The two are governed differently and the difference is not cosmetic.

On concentration, which is where I see people actually get hurt.

A compounded vial can be filled at a different concentration from the branded product you were previously using. If you carry over your old arithmetic — same number of units, different mg/mL — you draw a different amount and may not notice for weeks.

Read the label every time you switch. Redo the arithmetic on paper. Write the concentration on the vial. It is the same habit c/reconstitution keeps preaching and this is the case where it actually bites.

Why "compounded" is not "generic", written out because the confusion is constant.

A generic is an approved product demonstrated to be bioequivalent to a reference. A compounded preparation is made for a patient or, in the case of an outsourcing facility, under a different regulatory route entirely. It carries no equivalence claim and it is not required to demonstrate one.

That is not a quality judgement. Plenty of compounded preparations are made carefully in facilities with real testing programmes. It is a statement about what has and has not been established, and the difference matters when people assume the two are interchangeable.

Corrections welcome, especially the pedantic ones. Pedantry is how this board earns its reputation.