Injections or infusions may be contaminated with mobile and undissolved extraneous particles, which can pose a threat to patients receiving the treatments.

To minimise the risk of harm to the patient, pharmacopoeias include methods for the determination of sub-visible particle counts as well as corresponding maximum limits

Particle counting is carried out using USP and BP/EP pharmacopoeia-compliant techniques for parenteral/injectable solutions, ophthalmic solutions, medical devices and water. These techniques include:

  • Sub-visible particle counting using a light obscuration particle counter
  • Sub-visible particle counting investigation using a light microscope

Principle of test

Sub-visible particle counting using a light obscuration particle counter
Sub-visible particle counting using a light obscuration particle counter is carried out with the aid of a HIAC/ROYCO particle counter. It works on the principle of light blockage, which automatically determines the size and number of particles present in a sample. 

Sub-visible particle counting investigation using a light microscope
The sample undergoing the test is filtered and the membrane filter is manually examined under a binocular microscope for any particles.

Sample requirements

  • Container size >25 ml:  2-10 containers
  • Container size <25 ml:  10 or more containers required to obtain a pooled volume of not less than 40ml
  • Medical devices for infusion: 1-10 devices, as long as the total extracted volume is ≥ 40ml

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