Integrity Testing of Syringes

It is accepted that sterile plastic disposable syringes are used in clinical areas such as wards and theatres to administer injectable medicines. It has become accepted practice in pharmacies that are preparing injectable medicines to defined standards in the UK (Beaney 2006) [1]
, to use these same sterile plastic disposable syringes with attached sterile blind hubs to store injectable medicines. However, these devices were designed for immediate use and not as short- or long-term storage devices. It is therefore important that the integriry of the syringe and closure (hub) are maintained up to the time of injection.

Medicines prepared in glass ampoules can sometimes be autoclaved and in this case a methylene blue dye test is used to check all individual ampoules for cracks and holes that could hence compromise sterility. It is not possible to adopt a similar test for syringes, however a methylene blue dye intrusion method has been developed to test the integrity of batches of syringes and hub combinations. The test involves drilling a hole in a plunger, filling a syringe with water, pulling the plunger back and immersing the hub in a bath of methylene blue dye. The water in the syringe can then be analysed for the presence of the dye, which indicates lack of integrity.

There is an equivalent microbiological integrity test for syringe/hub combinations that uses syringes containing Tryptone Soy Broth as a general nutrient. The hub or plunger or both are placed in contact with a suspension of either Brevundimonas diminuta or Eschericia Coli (E coli). The contents of the syringe are examined after incubation for signs of growth. The test is carried out with the syringe plunger at the normal operating position and can be used to evaluate the plunger arrangement as well as the hub system. Brevundimonas diminuta is chosen because it is very small (0.3μm) organism and can move through cracks. E coli (0.5μm) is chosen as an alternative because it is a highly motile organism and can move easily through any small channel.

Both of these techniques have been successfully used to prevent the use of inappropriate syringe/hub combinations. Additionally they have been used to evaluate the design of neuraxial devices (for epidural administration) and needle-free syringe devices. Further details are available in a UK NHS Pharmaceutical Quality Assurance Committee advisory document [2].