The function of Sodium lauryl sulfate (SLS) in the formula below is? Hydrophilic Ointment, USP, has the following formula for 1,000 g: Methylparaben 0.25 g Propylparaben 0.15 g Sodium lauryl sulfate 10 g Propylene glycol 120 g Stearyl alcohol 250 g White petrolatum 250 g Purified water 370 g

Sodium lauryl sulfate is an anionic surfactant utilized in pharmaceutical compounding to lower surface tension between immiscible phases. It is a critical component of Hydrophilic Ointment, USP, which is an oil-in-water (o/w) emulsion. By stabilizing the interface between white petrolatum and purified water, it prevents phase separation and ensures a homogeneous preparation suitable for topical drug delivery. Rationale: A. A solvent is a substance, typically liquid, used to dissolve a solute to create a solution. While purified water and propylene glycol serve as the aqueous solvent system in this formula, SLS does not function to dissolve the solids. Its role is focused on interfacial stabilization rather than simple dissolution. B. The oleaginous phase of this ointment consists of white petrolatum and stearyl alcohol, which provide the emollient properties and greasy consistency. Sodium lauryl sulfate is an amphiphilic molecule that interacts with this phase but does not constitute the bulk oily base. Its concentration is too low to be a primary vehicle. C. Emulsifying agent is the correct function because SLS acts as a surfactant that facilitates the formation of an emulsion. It contains a hydrophilic head and a hydrophobic tail, allowing it to bridge the gap between the water and oil phases. This prevents the coalescence of droplets, ensuring the ointment remains stable over time. D. Antimicrobial preservatives like methylparaben and propylparaben are included in the formula to inhibit microbial growth in the water-containing base. While SLS has some minor antibacterial properties, it is not included in the USP formula for preservative efficacy. Its primary mechanical utility is purely as a stabilizer for the emulsion. E. Viscosity-enhancing agents are used to increase the thickness or "body" of a topical preparation. In this specific formula, stearyl alcohol primarily serves this structural purpose by providing stiffness to the ointment. SLS is used in a 10 g quantity, which is insufficient to significantly alter the overall viscosity of the 1,000 g batch.