Introduction: Propylene glycol (1,2-propanediol) is a versatile pharmaceutical excipient with a well-defined structure (C3H8O2) and key roles as a solvent, humectant, penetration enhancer, and stabilizer in formulations. B. Pharm students should understand its stereochemistry, production from propylene oxide, physicochemical properties (miscibility, viscosity, density), metabolism, safety profile and regulatory standards (USP). Mastery of propylene glycol’s structure and uses helps in excipient selection, compatibility assessment and risk evaluation in dosage form design. This topic is essential for formulation development, pharmacokinetics and toxicology studies. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the IUPAC name of propylene glycol?
- 1,2-propanediol
- 1,3-propanediol
- 2-propanol
- propan-1-ol
Correct Answer: 1,2-propanediol
Q2. What is the molecular formula of propylene glycol?
- C2H6O
- C3H8O2
- C3H6O
- C4H10O2
Correct Answer: C3H8O2
Q3. What is the approximate molecular weight of propylene glycol?
- 46.07 g/mol
- 60.10 g/mol
- 76.09 g/mol
- 92.14 g/mol
Correct Answer: 76.09 g/mol
Q4. Which functional groups are present in propylene glycol?
- One alcohol group
- Two alcohol groups
- One aldehyde group
- One ketone group
Correct Answer: Two alcohol groups
Q5. Propylene glycol is classified as which type of diol?
- Vicinal diol
- Geminal diol
- Terminal diol
- Conjugated diol
Correct Answer: Vicinal diol
Q6. Which physical property best describes propylene glycol at room temperature?
- Colorless, viscous liquid
- Yellow, volatile liquid
- Solid crystalline compound
- Colorless gas
Correct Answer: Colorless, viscous liquid
Q7. Propylene glycol is miscible with which of the following?
- Water only
- Ether only
- Water and ethanol
- Hydrocarbons only
Correct Answer: Water and ethanol
Q8. Which production method is the primary industrial route for propylene glycol?
- Hydration of ethylene oxide
- Hydration of propylene oxide
- Oxidation of glycerol
- Polymerization of propylene
Correct Answer: Hydration of propylene oxide
Q9. Propylene glycol has a chiral center. What is the commercial stereochemical form usually used?
- Pure R enantiomer
- Pure S enantiomer
- Racemic mixture
- Mesomeric form
Correct Answer: Racemic mixture
Q10. Which of the following best describes a major pharmaceutical use of propylene glycol?
- Active pharmaceutical ingredient for analgesia
- Solvent and co-solvent for poorly soluble drugs
- Primary preservative in parenteral products
- Buffering agent to control pH
Correct Answer: Solvent and co-solvent for poorly soluble drugs
Q11. In topical formulations propylene glycol is commonly used as:
- Emulsifier
- Humectant and skin penetration enhancer
- Primary active antimicrobial
- pH indicator
Correct Answer: Humectant and skin penetration enhancer
Q12. Which pharmacopoeia contains monographs for propylene glycol used in pharmaceuticals?
- USP (United States Pharmacopeia)
- BP only
- No pharmacopeia includes propylene glycol
- Only regional cosmetic compendia
Correct Answer: USP (United States Pharmacopeia)
Q13. Which analytical technique is commonly used to quantify propylene glycol in formulations?
- UV-visible spectrophotometry
- Gas chromatography (GC)
- Nuclear magnetic resonance for routine QC
- Titration with NaOH
Correct Answer: Gas chromatography (GC)
Q14. Propylene glycol is often preferred over ethylene glycol in pharmaceutical uses because:
- It is more toxic
- It has better flavor
- It has lower toxicity to humans
- It is cheaper to produce
Correct Answer: It has lower toxicity to humans
Q15. Which metabolic pathway primarily metabolizes propylene glycol in humans?
- Cytochrome P450 oxidation to carboxylic acids
- Alcohol dehydrogenase pathway to lactaldehyde then to lactic acid
- Glucuronidation and direct renal excretion unchanged
- Beta-oxidation in mitochondria
Correct Answer: Alcohol dehydrogenase pathway to lactaldehyde then to lactic acid
Q16. Excessive exposure to propylene glycol can lead to which adverse effect?
- Severe hemolytic anemia
- Lactic acidosis and CNS depression
- Permanent hearing loss
- Thyroid dysfunction
Correct Answer: Lactic acidosis and CNS depression
Q17. Which patient population is at higher risk for propylene glycol accumulation and toxicity?
- Healthy adults with normal renal function
- Neonates and patients with renal or hepatic impairment
- Patients with controlled hypertension
- Individuals with hyperthyroidism
Correct Answer: Neonates and patients with renal or hepatic impairment
Q18. Propylene glycol is classified pharmaceutically as which excipient type?
- Diluent for tablets
- Co-solvent and humectant
- Disintegrant
- Gelling agent
Correct Answer: Co-solvent and humectant
Q19. Which property of propylene glycol makes it useful as a solvent for parenteral injections?
- High volatility
- Good solubilizing power for many lipophilic drugs and relative biocompatibility
- Strong acidity
- High aromatic content
Correct Answer: Good solubilizing power for many lipophilic drugs and relative biocompatibility
Q20. Propylene glycol’s boiling point is closest to which value?
- 78 °C
- 100 °C
- 188 °C
- 250 °C
Correct Answer: 188 °C
Q21. Which statement about propylene glycol’s miscibility is true?
- It is immiscible with water
- It forms azeotropes with water only
- It is fully miscible with water and many organic solvents
- It dissolves only in nonpolar solvents
Correct Answer: It is fully miscible with water and many organic solvents
Q22. Which formulation type commonly uses propylene glycol as vehicle?
- Ointments only
- Oral syrups, topical gels, and parenteral injections
- Compressed tablets exclusively
- Dry powder inhalers only
Correct Answer: Oral syrups, topical gels, and parenteral injections
Q23. Which of these is a key difference between propylene glycol and glycerol?
- Glycerol is a diol while propylene glycol is a triol
- Propylene glycol is less viscous and has lower molecular weight than glycerol
- Both have identical boiling points
- Glycerol is not hygroscopic but propylene glycol is
Correct Answer: Propylene glycol is less viscous and has lower molecular weight than glycerol
Q24. In compatibility studies, propylene glycol can affect which property of a drug?
- Drug solubility and chemical stability
- Only tablet hardness
- Only color but not potency
- No effect on formulations
Correct Answer: Drug solubility and chemical stability
Q25. Propylene glycol acts as a cryoprotectant in some formulations because it:
- Raises freezing point
- Reduces ice crystal formation and protects biologicals during freezing
- Polymerizes at low temperatures
- Causes rapid dehydration
Correct Answer: Reduces ice crystal formation and protects biologicals during freezing
Q26. Which safety label is most appropriate for pharmaceutical-grade propylene glycol?
- Highly flammable liquid
- Harmful if swallowed in large amounts; use as directed
- Radioactive material
- Explosive when dry
Correct Answer: Harmful if swallowed in large amounts; use as directed
Q27. What is the primary reason propylene glycol is used in topical dermatological products?
- To act as a primary surfactant
- To enhance drug penetration and retain moisture
- To neutralize skin pH
- To provide antimicrobial sterilization
Correct Answer: To enhance drug penetration and retain moisture
Q28. Which of the following formulations might require assessment for propylene glycol-induced hemolysis?
- Topical cream for adults
- High-dose parenteral infusion containing propylene glycol vehicle
- Immediate-release tablet without PG
- Dry powder nasal spray
Correct Answer: High-dose parenteral infusion containing propylene glycol vehicle
Q29. Which regulatory consideration is important when selecting propylene glycol for pediatric formulations?
- Taste masking only
- Potential for metabolic accumulation and dose limits in infants
- Guaranteed lack of allergenicity
- It enhances tablet binding
Correct Answer: Potential for metabolic accumulation and dose limits in infants
Q30. Propylene glycol exhibits which of the following antimicrobial properties?
- Strong bactericidal action at low concentrations
- No antimicrobial activity whatsoever
- Some preservative-enhancing effects but not a primary preservative
- Fungicidal at trace levels
Correct Answer: Some preservative-enhancing effects but not a primary preservative
Q31. Which chemical is most structurally similar to propylene glycol?
- Ethylene glycol
- Glycerol
- Propionic acid
- Butanol
Correct Answer: Ethylene glycol
Q32. Which test would detect impurities of propylene glycol in a sample?
- Organoleptic testing only
- Gas chromatography with appropriate detectors
- Visual inspection for color change only
- pH meter reading
Correct Answer: Gas chromatography with appropriate detectors
Q33. In inhalation products (e.g., nebulizers), propylene glycol is used mainly as:
- Aerosol propellant
- Solvent and humectant to stabilize aerosols
- Primary active bronchodilator
- Carrier for dry powders only
Correct Answer: Solvent and humectant to stabilize aerosols
Q34. What effect does propylene glycol have on the skin when used in high concentrations?
- It always causes severe ulceration
- May cause irritation or contact dermatitis in sensitive individuals
- Completely prevents any skin irritation
- Promotes immediate tanning
Correct Answer: May cause irritation or contact dermatitis in sensitive individuals
Q35. Which statement is true about propylene glycol’s pKa?
- It has a pKa around 4.5 indicating acidity
- It does not have an ionizable functional group with a relevant pKa in physiological range
- Its pKa is essential for acting as a buffer
- It is a strong base
Correct Answer: It does not have an ionizable functional group with a relevant pKa in physiological range
Q36. In compatibility testing, propylene glycol may accelerate degradation of drugs that are:
- Stable in all solvents
- Hydrolytically unstable or reactive with alcohols
- Only stable as solids
- Inert to redox reactions
Correct Answer: Hydrolytically unstable or reactive with alcohols
Q37. Which storage condition is generally recommended for propylene glycol used in pharmaceuticals?
- Open containers at high humidity
- Sealed, at controlled room temperature away from strong oxidizers
- Frozen at -80°C
- Exposed to direct sunlight
Correct Answer: Sealed, at controlled room temperature away from strong oxidizers
Q38. Which statement regarding propylene glycol and parenteral admixtures is correct?
- It is never used in parenteral products
- Used with caution due to possible accumulation and toxicity at high doses
- Always safe in unlimited quantities intravenously
- It is a primary anticoagulant
Correct Answer: Used with caution due to possible accumulation and toxicity at high doses
Q39. What is a common role of propylene glycol in oral liquid formulations?
- To act as sweetener only
- To serve as solvent for active ingredient and improve mouthfeel
- To act as a preservative replacing all others
- To cause rapid precipitation of the drug
Correct Answer: To serve as solvent for active ingredient and improve mouthfeel
Q40. Which metabolic product is directly associated with propylene glycol metabolism?
- Ethylene glycol
- Lactate
- Acetylsalicylic acid
- Formaldehyde
Correct Answer: Lactate
Q41. Which analytical parameter is critical to check for pharmaceutical-grade propylene glycol?
- Optical rotation only
- Purity and residual propylene oxide and heavy metals
- Protein content
- Presence of starch
Correct Answer: Purity and residual propylene oxide and heavy metals
Q42. Propylene glycol can be used to improve dermal delivery by:
- Forming permanent covalent bonds with skin proteins
- Disrupting stratum corneum lipid structure and improving solute partitioning
- Increasing corneal thickness
- Neutralizing skin pH to alkaline
Correct Answer: Disrupting stratum corneum lipid structure and improving solute partitioning
Q43. Which of the following is NOT a typical use of propylene glycol in pharmacy?
- Excipient in oral syrups
- Vehicle for topical gels
- Active antihypertensive agent
- Co-solvent in parenteral formulations
Correct Answer: Active antihypertensive agent
Q44. Which statement about propylene glycol and regulatory status is correct?
- It is banned from all pharmaceutical products
- It is accepted by major pharmacopeias with quality specifications
- It is classified as a controlled narcotic
- It requires a prescription to purchase
Correct Answer: It is accepted by major pharmacopeias with quality specifications
Q45. Which excipient property is enhanced by adding propylene glycol to a topical gel?
- Thermal conductivity only
- Hydration of stratum corneum and solubility of actives
- Solid content of gel
- Ability to polymerize into a film-forming plastic
Correct Answer: Hydration of stratum corneum and solubility of actives
Q46. Which precaution is important when formulating with propylene glycol for neonates?
- No precautions needed; neonates metabolize it faster
- Limit total daily exposure due to immature metabolism and renal excretion
- Always substitute with ethylene glycol
- Only topical use is allowed
Correct Answer: Limit total daily exposure due to immature metabolism and renal excretion
Q47. In formulation development, propylene glycol is often evaluated for:
- Its polymerization tendency
- Solubility enhancement, stability effects, and compatibility with APIs and packaging
- Its nutritional calorie content
- Its radioactivity
Correct Answer: Solubility enhancement, stability effects, and compatibility with APIs and packaging
Q48. Which container-closure concern applies to propylene glycol-containing formulations?
- Strongly acidic containers are required
- Migration of plasticizers from PVC may occur; compatibility must be assessed
- Glass reacts violently with PG
- Metal containers are universally incompatible
Correct Answer: Migration of plasticizers from PVC may occur; compatibility must be assessed
Q49. Which method is appropriate to reduce propylene glycol toxicity in an acute overdose?
- Administration of ethanol or fomepizole to inhibit alcohol dehydrogenase may be considered
- Immediate dialysis is always contraindicated
- Give activated charcoal orally only
- No treatment is necessary
Correct Answer: Administration of ethanol or fomepizole to inhibit alcohol dehydrogenase may be considered
Q50. Which statement best summarizes propylene glycol’s role in pharmacy?
- An essential active drug used to treat infections
- A versatile excipient used as solvent, humectant and penetration enhancer but requiring safety assessment for vulnerable patients
- Completely inert and requires no quality control
- Used exclusively in industrial paints and not in pharmaceuticals
Correct Answer: A versatile excipient used as solvent, humectant and penetration enhancer but requiring safety assessment for vulnerable patients
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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