sterilization
Sterilization is the process of making something completely free of living microbes — bacteria, fungi, viruses and, crucially, their tough dormant spores. Disinfection merely reduces germs to a safe level; sterilization aims to leave none at all. For a product injected into the body, that absolute target is the whole point.
Because absolute certainty is impossible to prove on every single unit, sterility is defined statistically. A validated terminal process is designed to give a sterility assurance level (SAL) of no more than one chance in a million that a given item still harbours a viable organism. The process is qualified once, then monitored every run, rather than tested for sterility on the entire batch.
There are four broad routes. Moist heat (steam under pressure, autoclaving) and dry heat kill by cooking microbes; filtration physically strains them out of a heat-sensitive liquid; gas (such as ethylene oxide) and radiation sterilize items that cannot tolerate heat. Wherever the product can survive it, terminal sterilization in the sealed final container is preferred because it sterilizes the actual finished item.
An honest caveat: sterility is a property of the whole process and packaging, not a magic ingredient you add. A perfectly sterilized solution sealed in a leaking container is no longer sterile, which is why container-closure integrity matters as much as the kill step itself.
A bag of saline that can withstand heat is sealed and then autoclaved at 121°C, giving terminal sterilization of the finished product; a heat-labile protein solution instead relies on filtration sterilization and aseptic filling.
Pick the method by what the product can survive — and prefer terminal sterilization where possible.
Sterilization removes living organisms but does not destroy pyrogens. Bacterial endotoxins survive autoclaving, so a depyrogenation step (such as dry heat at very high temperature for glass) is needed separately to inactivate them.