The most commonly used method by compounding pharmacies to sterilize ophthalmic preparations is:
a. Autoclaving
b. Sterile membrane filtration
c. Boiling in a water bath
d. Adding a microbial preservative to the preparation
The correct answer and explanation is:
The correct answer is: a. Autoclaving
Explanation:
Autoclaving is the most commonly used method by compounding pharmacies to sterilize ophthalmic preparations. This is because ophthalmic products (eye drops, ointments) must be sterile to prevent infections when applied to the eyes, which are highly sensitive and susceptible to contamination.
Why Autoclaving?
- Effective Sterilization: Autoclaving uses saturated steam under pressure (usually at 121°C for 15–20 minutes) to kill all forms of microbial life, including bacteria, viruses, spores, and fungi. This makes it a very reliable sterilization technique.
- Widely Applicable: It can be used for a variety of ophthalmic preparations that can tolerate heat and moisture.
- Standardized and Accepted: Autoclaving is an industry-standard method for sterilization in pharmaceutical compounding and production.
Why Not the Other Options?
- b. Sterile membrane filtration:
This method is also used in sterilizing ophthalmic solutions, particularly heat-sensitive ones that cannot withstand autoclaving. Membrane filtration passes the solution through a 0.22-micron filter to physically remove microorganisms. However, it is more common for solutions that cannot tolerate heat. While important, it is less commonly used than autoclaving overall in compounding pharmacies, especially for preparations that tolerate heat. - c. Boiling in a water bath:
Boiling (at 100°C) is not an effective sterilization method because it does not kill spores and some heat-resistant microbes. It is a disinfection method but not reliable for full sterilization required in ophthalmics. - d. Adding a microbial preservative:
Preservatives such as benzalkonium chloride are added to multi-dose ophthalmic solutions to prevent microbial growth after opening but do not sterilize the product initially. They are supplemental to sterilization but do not replace it.
Additional Context:
Sterilization of ophthalmic products is critical because the eye is a sterile environment. Contamination can lead to serious infections such as keratitis or endophthalmitis. Compounding pharmacies must ensure their preparations are sterile by validated sterilization methods. Autoclaving is generally preferred for its proven efficacy and relatively low cost.
In cases where formulations are heat-sensitive (e.g., protein-based drugs), sterile filtration may be used, followed by aseptic filling under sterile conditions. However, autoclaving remains the most common and practical approach for many compounded ophthalmic solutions.