Question:
Which of the following is commonly used as a broad-spectrum preservative in pharmaceutical formulations?
Which of the following is commonly used as a broad-spectrum preservative in pharmaceutical formulations?
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Benzalkonium chloride provides broad antimicrobial protection, especially useful in aqueous multi-dose formulations.
Updated On: Jul 14, 2026
- Benzoic acid
- Benzalkonium chloride
- Ascorbic acid
- Vitamin C
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The Correct Option is B
Approach Solution - 1
Benzalkonium chloride is a quaternary ammonium compound widely used as a broad-spectrum antimicrobial preservative in various pharmaceutical formulations, including ophthalmic solutions, nasal sprays, and topical preparations.
It is effective against bacteria, fungi, and some viruses, making it a preferred preservative for multi-dose formulations. Its mechanism of action involves disruption of microbial cell membranes, leading to leakage of cellular contents and cell death.
In contrast:
- Benzoic acid is used primarily as a preservative in acidic preparations such as syrups and beverages but has a narrower spectrum of activity.
- Ascorbic acid and Vitamin C are antioxidants, not primarily used as antimicrobial preservatives.
Due to its broad efficacy and relatively low toxicity at recommended concentrations, benzalkonium chloride remains a common choice for preservation in pharmaceutical products.
- Ascorbic acid and Vitamin C are antioxidants, not primarily used as antimicrobial preservatives.
Due to its broad efficacy and relatively low toxicity at recommended concentrations, benzalkonium chloride remains a common choice for preservation in pharmaceutical products.
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Approach Solution -2
This question is looking for the compound among the four listed that acts as a broad-spectrum antimicrobial preservative. Checking what each substance actually does in a formulation, rather than just its name, separates the true preservative from the others.
- Benzoic acid: Benzoic acid is used as a preservative, but mainly in acidic formulations such as syrups, since it only stays in its active, un-ionized form at low pH. Its spectrum and effectiveness are narrower and more pH-dependent than a broad-spectrum agent.
- Benzalkonium chloride: This quaternary ammonium compound disrupts the cell membranes of bacteria, fungi, and some viruses, and it stays effective across a wide pH range. That combination of a wide range of target organisms and reliable activity across formulations is what makes it a broad-spectrum preservative, used in eye drops, nasal sprays, and topical products.
- Ascorbic acid: Ascorbic acid is vitamin C, an antioxidant that protects a formulation from oxidative degradation. It does not kill or inhibit microorganisms, so it is not a preservative at all.
- Vitamin C: This is the same compound as ascorbic acid, so it carries the same antioxidant role and the same lack of antimicrobial action.
Only benzalkonium chloride combines antimicrobial action against a wide range of organisms with stability across different formulation types, which is what broad-spectrum preservative describes.
So the correct answer is Benzalkonium chloride.
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