Which method is typically used to sterilize heat-labile liquids?

• A. Filtration
• B. Steam (moist heat)
• C. Ethylene oxide
• D. Dry heat

Answer: (A)

When a liquid cannot tolerate heat, the usual approach is to sterilize by removing microorganisms with a sterile-grade filter. Sterile filtration uses a membrane with a very small pore size (commonly around 0.2–0.22 μm) to physically retain bacteria and most fungi as the liquid is pushed through under pressure, yielding a sterile product without heating the liquid. This preserves heat-sensitive components and is widely used for parenteral and other heat-labile solutions.

Keep in mind limitations: some viruses may pass through standard sterilizing membranes, and particulates or high viscosity can clog the filter. The filter material must be compatible with the liquid, and the integrity of the filter must be validated before and after use to ensure sterility. Other methods rely on heat or chemical residues, which can damage the liquid or leave undesirable residues, making them unsuitable for sterilizing heat-labile solutions.