Sterile water for injection (revision 8)

Sterile water for injection is water that has been sterilised and meets compendial requirements for particulates, endotoxin and conductivity, supplied without preservative, buffer or tonicity agent. It is intended for single use in preparing an injection.^[1]

Because it contains no preservative, a container that has been entered offers no barrier to growth of organisms introduced at entry, and it is therefore packaged and used as single-entry. This is the operative difference from bacteriostatic water.^[2]

It is also hypotonic. Water alone is not isotonic with tissue, so a preparation reconstituted in it is hypotonic unless the solute makes it otherwise, which for a few milligrams of peptide it does not.^[1]

The relevant monograph specifies sterility, freedom from pyrogens, limits on conductivity and total organic carbon, and particulate matter limits. It is prepared by distillation or by a purification process of equivalent capability, and it is not simply purified water in a sealed container.^[1]

Sterility of the water is not the same as sterility of the preparation made from it. A non-sterile powder reconstituted in sterile water yields a non-sterile solution, and the water's compendial status does not transfer. See Sterility testing.

Endotoxin limits apply to the water because endotoxin survives sterilisation. Water systems are the classic source of endotoxin contamination, and controlling them is a manufacturing rather than a testing exercise.^[3]