Question

As per USP, the maximum concentration of benzalkonium chloride used as a preservative in parenteral formulations is

• A. 0.01%
• B. 0.001%
• C. 0.05%
• D. 0.005%

Hint:

Always adhere to USP limits for preservatives in parenteral formulations to balance antimicrobial efficacy and patient safety.

Answer 1

The Correct Option is A

Benzalkonium chloride is a quaternary ammonium compound widely used as a preservative due to its antimicrobial properties. In parenteral formulations, preservatives are required to prevent microbial contamination during storage and use. According to the United States Pharmacopeia (USP) guidelines, the maximum permissible concentration of benzalkonium chloride in parenteral (injectable) formulations is 0.01%. Higher concentrations may pose toxicity risks such as irritation or sensitization. Therefore, strict limits ensure safety while maintaining effective antimicrobial activity. Using benzalkonium chloride within this concentration helps maintain sterility without compromising patient safety, which is crucial for injectable drug products.

Answer 2

This question is checking the maximum allowed strength of benzalkonium chloride when it is used to preserve an injectable formulation. Comparing the listed concentrations against how this preservative is actually used in practice narrows down the right one.

1. 0.01%: This is the concentration most pharmacopeial references cite as the upper limit for benzalkonium chloride in parenteral products. At this strength it still gives reliable antimicrobial protection to a multi-dose injectable without crossing into the concentration range where local tissue irritation becomes a concern.
2. 0.001%: This is ten times weaker than the accepted ceiling. A concentration this low would not reliably control microbial growth across the shelf life of a multi-dose injection, so it undershoots the working range rather than defining its upper limit.
3. 0.05%: This is five times higher than the accepted maximum. Quaternary ammonium preservatives like benzalkonium chloride become more likely to irritate tissue and cause hemolysis at higher strengths, which is why formulations are kept well below this level for parenteral use.
4. 0.005%: This concentration is below the standard maximum and would normally still preserve a formulation adequately, but it is not the ceiling value the question is asking for, it is simply a lower strength that is also permitted.

Weighing effective antimicrobial action against the risk of irritation at higher strengths, the concentration cited as the maximum for benzalkonium chloride in parenteral formulations is 0.01%.

So the correct answer is 0.01%.