The function of Sodium lauryl sulfate (SLS) in the formula below is?
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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 |
Solvent.
Constituting the oleaginous phase.
Emulsifying agent.
Antimicrobial preservative.
Viscosity-enhancing agent.
The Correct Answer is C
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.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
The bacterial cell envelope structure is the primary basis for the Gram stain classification. Gram-positive bacteria have a thick, multi-layered peptidoglycan wall containing teichoic acids. In contrast, Gram-negative bacteria have a much thinner peptidoglycan layer but possess an asymmetrical outer membrane. This outer membrane contains specialized molecules that act as a barrier to certain antibiotics and function as powerful endotoxins during systemic infections.
Rationale:
A. Peptidoglycan is found in both Gram-positive and Gram-negative bacteria. It is the structural polymer that provides the cell its shape and protects it from osmotic lysis. While the thickness varies significantly—thick in Gram-positive and thin in Gram-negative—it is a universal component of most eubacterial cell walls and thus not unique.
B. Flagella are complex protein structures used for motility and can be found on both Gram-positive and Gram-negative species. They are not a distinguishing feature of the cell wall type. The presence of flagella depends on the specific genus and species and their need to move toward nutrients or away from toxins.
C. Lipid A is the correct answer as it is the innermost component of the lipopolysaccharide (LPS) found exclusively in the outer membrane of Gram-negative bacteria. It acts as a potent endotoxin that triggers a massive immune response, potentially leading to septic shock. Gram-positive bacteria lack an outer membrane and therefore do not possess Lipid A.
D. A capsule is an organized layer of polysaccharides located outside the cell wall that can be present in either Gram-positive or Gram-negative bacteria. It serves as a virulence factor by helping the bacteria evade phagocytosis. Because it is found in diverse groups like Streptococcus (positive) and Klebsiella (negative), it is not a defining difference.
E. Pili (or fimbriae) are hair-like appendages used for attachment or genetic exchange (conjugation). While they were historically associated more with Gram-negative bacteria, many Gram-positive bacteria are now known to possess similar structures. Therefore, they are not a reliable exclusive component of Gram-negative organisms for the purpose of differential classification.
Correct Answer is D
Explanation
Step 1. Convert micrograms to milligrams.
480 ug / 1,000 = 0.48 mg.
Step 2. Calculate mg per mL.
0.48 mg / 0.8 mL = 0.6 mg/mL.
Step 3. Convert to percentage (w/v).
Percentage = (grams / 100 mL).
0.6 mg = 0.0006 g.
(0.0006 g / 1 mL) = (X / 100 mL).
X = 0.06 g.
Concentration = 0.06%.
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