October 13, 2021: Pharmaceutical Interview Questions and Answers
#DirectInoculationOfTheCultureMediumForSterilityTesting
1. Explain the direct inoculation of the culture medium for sterility testing?
● Transfer the quantity of the preparation to be examined prescribed in following Table directly into the culture medium so that the volume of the product is not more than 10% of the volume of the medium, unless otherwise prescribed.
Table: 1 – Liquids samples
| Minimum quantity to be used for each medium Quantity per container | Minimum quantity to be used for each medium unless otherwise justified and authorized |
| • less than 1 ml | The whole contents of each container |
| • 1-40 ml | Half the contents of each container but not less than 1 ml |
| • greater than 40 ml and not greater than 100 ml | 20 ml |
| • greater than 100 ml | 10 per cent of the contents of the container but not less than 20 ml |
| Antibiotic liquids | 1 ml |
Table: 2 – Insoluble preparations, creams and ointments samples
| Minimum quantity to be used for each medium Quantity per container | Minimum quantity to be used for each medium unless otherwise justified and authorized |
| Insoluble preparations, creams and ointments to be suspended or emulsified | Use the contents of each container to provide not less than 200 mg |
Table: 3 – Solids samples
| Minimum quantity to be used for each medium Quantity per container | Minimum quantity to be used for each medium unless otherwise justified and authorized |
| • less than 50 mg | The whole contents of each container |
| • 50 mg or more but less than 300 mg | Half the contents of each container but not less than 50 mg |
| • 300 mg – 5 g | 150 mg |
| • greater than 5 g | 500 mg |
● If the product to be examined has antimicrobial activity, carry out the test after neutralizing this with a suitable neutralizing substance or by dilution in a sufficient quantity of culture medium.
● When it is necessary to use a large volume of the product it may be preferable to use a concentrated culture medium prepared in such a way that it takes account of the subsequent dilution.
● Where appropriate the concentrated medium may be added directly to the product in its container.
Oily liquids:
● Use media to which have been added a suitable emulsifying agent at a concentration shown to be appropriate in the method suitability of the test, for example polysorbate 80 at a concentration of 10 g/l.
Ointments and creams:
● Prepare by diluting to about 1 in 10 by emulsifying with the chosen emulsifying agent in a suitable sterile diluent such as peptone (1 g/l) TS1.
● Transfer the diluted product to a medium not containing an emulsifying agent.
● Incubate the inoculated media for not less than 14 days. Observe the cultures several times during the incubation period.
● Shake cultures containing oily products gently each day. However when fluid thioglycollate medium is used for the detection of anaerobic microorganisms keep shaking or mixing to a minimum in order to maintain anaerobic conditions.
Reference: WHO, Document QAS/11.413 FINAL, March 2012