Photostability Testing: Guidelines, study design and interpretation MCQs With Answer

Introduction

Photostability Testing: Guidelines, study design and interpretation MCQs With Answer is a focused quiz collection designed for M. Pharm students studying advanced pharmaceutical analysis. This resource summarizes regulatory expectations, practical study design, analytical considerations and interpretation of photostability results based on ICH guidance and industry practice. Questions cover light sources, exposure criteria, dosimetry, sample selection, packaging evaluation, identification of photodegradation products and decision-making for formulation or packaging changes. Each MCQ includes concise options and a clear correct answer to help students build conceptual understanding and prepare for examinations and laboratory applications in formulation development and stability testing.

Q1. Which ICH guideline specifically addresses photostability testing of new drug substances and products?

• ICH Q1A(R2)
• ICH Q1B
• ICH Q2(R1)
• ICH Q3A

Correct Answer: ICH Q1B

Q2. What is the primary objective of photostability testing?

• To measure melting point changes caused by light
• To determine susceptibility to light-induced degradation and identify photodegradation products
• To evaluate microbial contamination after light exposure
• To assess packaging mechanical strength under sunlight

Correct Answer: To determine susceptibility to light-induced degradation and identify photodegradation products

Q3. According to ICH Q1B, what are the recommended light exposure targets for photostability testing?

• 100,000 lux hours and 50 watt-hours/m² (300–400 nm)
• 1.2 million lux hours and 200 watt-hours/m² (300–400 nm)
• 500,000 lux hours and 100 watt-hours/m² (320–400 nm)
• 2 million lux hours and 400 watt-hours/m² (250–350 nm)

Correct Answer: 1.2 million lux hours and 200 watt-hours/m² (300–400 nm)

Q4. Which light-source strategy is recommended by ICH Q1B for reproducible photostability testing?

• Only incandescent bulbs to simulate indoor lighting
• Cool white fluorescent lamps combined with near-UV lamps, or a xenon-arc lamp
• Only LED sources with unknown spectral output
• Sunlight exposure without any spectral control

Correct Answer: Cool white fluorescent lamps combined with near-UV lamps, or a xenon-arc lamp

Q5. Why are control samples wrapped in aluminum foil included in photostability studies?

• To accelerate degradation by heat
• To serve as dark controls protected from light for comparison
• To increase humidity around the sample
• To provide a reflective surface to increase light dose

Correct Answer: To serve as dark controls protected from light for comparison

Q6. Which sample types should typically be included in photostability testing?

• Only placebo formulations without API
• Only the bulk drug substance, not the finished product
• Both drug substance and finished drug product, including marketed primary packaging as appropriate
• Only stability samples stored at 40°C/75% RH

Correct Answer: Both drug substance and finished drug product, including marketed primary packaging as appropriate

Q7. Which elements should a photostability test protocol include?

• Light source and exposure conditions, sample description, and analytical methods
• Only the brand of the light source
• Temperature ramp program with no light parameters
• Only packaging color information

Correct Answer: Light source and exposure conditions, sample description, and analytical methods

Q8. Which instrument is used to measure illuminance in lux for photostability testing?

• Spectrophotometer
• Lux meter (photometer)
• Anemometer
• Thermocouple

Correct Answer: Lux meter (photometer)

Q9. What does the 200 watt‑hours/m² parameter represent in photostability testing?

• The total visible light energy across 400–700 nm
• The integrated near‑ultraviolet radiant energy delivered (typically 300–400 nm)
• The energy required to heat a sample by 10°C
• The power consumption of the photostability chamber

Correct Answer: The integrated near‑ultraviolet radiant energy delivered (typically 300–400 nm)

Q10. Chemical actinometry (e.g., potassium ferrioxalate) in photostability studies is used to measure what?

• Sample pH after irradiation
• Photon flux or radiant energy delivered to the sample
• Relative humidity inside the chamber
• Concentration of degradants by colorimetry

Correct Answer: Photon flux or radiant energy delivered to the sample

Q11. If a drug product shows significant degradation (for example >5%) after ICH‑specified light exposure, the correct interpretation is:

• The product is photostable and no action is needed
• The product is photolabile and protective measures such as light‑protective packaging or formulation changes should be considered
• Only increase the storage temperature and retest
• Discard the product immediately without further evaluation

Correct Answer: The product is photolabile and protective measures such as light‑protective packaging or formulation changes should be considered

Q12. What does achieving mass balance in a photostability study mean?

• The sum of recovered parent drug and identified degradation products approximates the initial amount
• The product weight remains unchanged after irradiation
• The packaging weight equals the drug weight
• All degradants are volatile and lost during testing

Correct Answer: The sum of recovered parent drug and identified degradation products approximates the initial amount

Q13. Which spectral range is generally defined as near ultraviolet for photostability dosimetry?

• 100–200 nm
• 200–280 nm
• 300–400 nm
• 500–700 nm

Correct Answer: 300–400 nm

Q14. What is the primary advantage of using a xenon‑arc lamp in photostability testing?

• It emits only infrared radiation
• It provides a broad spectrum approximating natural sunlight, including UV and visible regions
• It is the cheapest option with no need for dosimetry
• It does not require temperature control

Correct Answer: It provides a broad spectrum approximating natural sunlight, including UV and visible regions

Q15. Why must packaging be evaluated during photostability testing of finished products?

• Packaging always accelerates degradation
• Packaging can transmit, absorb or block light and therefore influences product photostability
• Packaging color only affects taste
• Packaging temperature determines photolysis

Correct Answer: Packaging can transmit, absorb or block light and therefore influences product photostability

Q16. How does photostability testing differ from general forced‑degradation studies?

• Photostability uses controlled light exposure per regulatory criteria; forced degradation uses a range of extreme stress conditions to generate degradants for method development
• Forced degradation is only performed under dark conditions
• Photostability always uses higher temperature than forced degradation
• There is no difference; they are identical tests

Correct Answer: Photostability uses controlled light exposure per regulatory criteria; forced degradation uses a range of extreme stress conditions to generate degradants for method development

Q17. In solid oral dosage forms, photodegradation is most likely to originate from which region?

• The tablet core deep inside
• The tablet surface or outer layers exposed to light
• The dissolution medium only after ingestion
• The packaging interior gas atmosphere

Correct Answer: The tablet surface or outer layers exposed to light

Q18. Which analytical approach is most appropriate to monitor photodegradation in stability studies?

• A stability‑indicating HPLC or LC‑MS method able to separate parent and photoproducts
• A simple UV color comparison without separation
• Only pH measurement
• Visual inspection for color change as the sole method

Correct Answer: A stability‑indicating HPLC or LC‑MS method able to separate parent and photoproducts

Q19. Which parameter is NOT directly specified as a dosimetric measure in standard photostability tests?

• Lux‑hours (illuminance over time)
• Integrated near‑UV energy (watt‑hours/m²)
• Relative humidity inside the exposure chamber
• Spectral irradiance distribution of the light source

Correct Answer: Relative humidity inside the exposure chamber

Q20. When significant photodegradation is observed, which corrective actions are appropriate?

• Change to light‑protective primary packaging
• Modify formulation (e.g., add UV stabilizers or opaque coating) or adjust labeling to protect from light
• Conduct additional identification and toxicological assessment of photoproducts
• All of the above

Correct Answer: All of the above

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