Bioassay of digitalis MCQs With Answer

Introduction: The bioassay of digitalis MCQs With Answer provides B. Pharm students a focused review of cardiac glycoside pharmacology, bioassay techniques, potency estimation, and therapeutic implications. This concise guide emphasizes digitalis (digoxin, digitoxin) mechanism of action on Na+/K+‑ATPase, inotropic effects, assay tissues (isolated frog heart, atria), experimental design (parallel line and slope‑ratio assays), sources of variability, statistical evaluation, and modern analytical alternatives like HPLC and LC‑MS. Understanding bioassay principles, sensitivity, relative potency calculations, and regulatory validation is essential for drug standardization and safe clinical use. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is a biological assay (bioassay)?

• A laboratory technique to measure the biological response produced by a substance
• A chemical method to determine molecular weight
• An imaging technique for tissue distribution
• A genomic assay to detect mutations

Correct Answer: A laboratory technique to measure the biological response produced by a substance

Q2. What is the primary objective of a bioassay of digitalis?

• Determine potency and standardization of the active substance
• Measure chemical contaminants in raw material
• Determine tablet dissolution profile only
• Assess drug‑excipient compatibility

Correct Answer: Determine potency and standardization of the active substance

Q3. Which are the main cardiac glycosides in Digitalis species?

• Digoxin and digitoxin
• Atropine and nicotine
• Propranolol and metoprolol
• Warfarin and heparin

Correct Answer: Digoxin and digitoxin

Q4. What is the primary mechanism of action of digitalis?

• Inhibition of Na+/K+‑ATPase leading to increased intracellular Ca2+
• Blockade of beta‑adrenergic receptors
• Inhibition of acetylcholinesterase
• Opening of potassium channels to hyperpolarize cells

Correct Answer: Inhibition of Na+/K+‑ATPase leading to increased intracellular Ca2+

Q5. Which classical tissue preparation is most commonly used for the bioassay of digitalis?

• Isolated frog heart (ventricle)
• Rat liver homogenate
• Human blood plasma
• Isolated guinea pig ileum

Correct Answer: Isolated frog heart (ventricle)

Q6. Which pharmacological parameter is primarily measured in digitalis bioassays using isolated heart preparations?

• Force of contraction (inotropy)
• Renal clearance rate
• Hepatic enzyme induction
• Neuromuscular blockade

Correct Answer: Force of contraction (inotropy)

Q7. What is an advantage of a biological assay compared to a purely chemical assay for digitalis?

• It measures actual biological activity (potency) rather than just chemical content
• It is always faster and cheaper
• It requires no controls or standards
• It is immune to biological variability

Correct Answer: It measures actual biological activity (potency) rather than just chemical content

Q8. Which assay design is commonly used to estimate relative potency in digitalis bioassays?

• Parallel line assay
• Randomized crossover assay
• Case‑control assay
• Single point comparison only

Correct Answer: Parallel line assay

Q9. In bioassay terminology, what does ED50 represent?

• The dose producing 50% of the maximal effect
• The dose causing 50% mortality
• The time to 50% absorption
• The enzyme degradation at 50% pH

Correct Answer: The dose producing 50% of the maximal effect

Q10. Why is a standard (reference) digitalis preparation necessary in bioassays?

• To compare sample potency against a known reference
• To sterilize assay tissues
• To act as a placebo control
• To determine tablet hardness

Correct Answer: To compare sample potency against a known reference

Q11. Which statistical approach is commonly used to test parallelism between dose‑response lines?

• Analysis of variance (ANOVA) for parallelism
• Chi‑square test for independence
• Kaplan‑Meier survival analysis
• Fisher’s exact test

Correct Answer: Analysis of variance (ANOVA) for parallelism

Q12. What is a major source of variability in classical bioassays of digitalis?

• Biological variability between assay tissues
• Instrumental drift in spectrophotometers only
• pH of unrelated solutions far from the assay
• Color of the reagent bottles

Correct Answer: Biological variability between assay tissues

Q13. Which modern analytical methods have largely supplemented classical bioassays for digitalis quantification?

• HPLC and LC‑MS for quantification
• Gel electrophoresis
• X‑ray crystallography of formulations
• Northern blotting

Correct Answer: HPLC and LC‑MS for quantification

Q14. How is the therapeutic index defined?

• Ratio of toxic dose to effective dose
• Difference between Cmax and Tmax
• Rate of absorption divided by elimination rate
• Percentage of protein binding

Correct Answer: Ratio of toxic dose to effective dose

Q15. Which clinical sign is classically associated with digitalis toxicity?

• Visual disturbances such as yellow‑green halos
• Severe hearing loss
• Hyperglycemia with glycosuria
• Profound neutropenia

Correct Answer: Visual disturbances such as yellow‑green halos

Q16. What ionic change mediates the increased contractility produced by digitalis?

• Increased intracellular Ca2+ via altered Na+/Ca2+ exchange
• Decreased intracellular Cl‑ concentration
• Increased extracellular K+ uptake only
• Direct activation of voltage‑gated Ca2+ channels without Na+ involvement

Correct Answer: Increased intracellular Ca2+ via altered Na+/Ca2+ exchange

Q17. In a parallel line assay, which term describes the potency comparison between sample and standard?

• Relative potency (ratio to standard)
• Absolute molecular weight
• Solubility index
• Partition coefficient

Correct Answer: Relative potency (ratio to standard)

Q18. In dose‑response analysis, what does the slope represent?

• The steepness of the dose‑response relationship
• The color change of the assay reagent
• The pH sensitivity of the drug
• The melting point of the compound

Correct Answer: The steepness of the dose‑response relationship

Q19. Why are multiple dose levels used in a bioassay?

• To construct a dose‑response curve and estimate potency parameters
• To reduce the number of replicates needed to one
• To ensure every tissue receives a toxic dose
• To prove color stability across concentrations

Correct Answer: To construct a dose‑response curve and estimate potency parameters

Q20. How is assay sensitivity defined in the context of bioassays?

• The ability to detect small differences in potency between preparations
• The pH range over which the assay functions
• The maximum temperature tolerated by tissues
• The shelf life of the standard solution

Correct Answer: The ability to detect small differences in potency between preparations

Q21. Which control is essential to account for non‑drug effects in a biological assay?

• Vehicle (negative) control
• Random noise control
• Color‑matched placebo only
• Control without tissue or instrument

Correct Answer: Vehicle (negative) control

Q22. What is the purpose of conducting stability (storage) studies for digitalis preparations?

• To assess potency changes over time under defined conditions
• To measure the tablet hardness only
• To determine taste masking efficiency
• To evaluate manufacturing yield

Correct Answer: To assess potency changes over time under defined conditions

Q23. Which formula is used to express percent potency of a test sample relative to a standard?

• (Sample potency / Standard potency) × 100%
• (Standard weight / Sample weight) × 100%
• (Sample volume / Buffer volume) × 100%
• (Absorbance of blank / Absorbance of sample) × 100%

Correct Answer: (Sample potency / Standard potency) × 100%

Q24. What is an important ethical concern when performing classical bioassays of digitalis?

• Use of live animals and isolated tissues
• Use of hazardous chemicals only for cleaning glassware
• Use of copyrighted assay methods
• Use of disposable pipette tips

Correct Answer: Use of live animals and isolated tissues

Q25. What does the requirement of parallelism in a parallel line assay mean?

• Dose‑response lines have similar slopes
• Both lines must have identical intercepts only
• Both lines must pass through the origin only
• Both lines must be non‑linear

Correct Answer: Dose‑response lines have similar slopes

Q26. When is the slope‑ratio assay preferred over the parallel line assay?

• When dose‑response relationships are linear and have a common intercept (pass through origin)
• When responses are clearly non‑linear and variable
• When no reference standard is available
• When only a single dose can be tested

Correct Answer: When dose‑response relationships are linear and have a common intercept (pass through origin)

Q27. In bioassay practice, what is a “blank” sample?

• A sample without active principle used to measure background response
• The highest concentration of test compound
• A replicate of the standard solution
• A tissue soaked only in saline for 24 hours

Correct Answer: A sample without active principle used to measure background response

Q28. Which instrument is typically used to measure contractile force in isolated heart bioassays?

• Force transducer (isometric myograph)
• Gas chromatograph
• Ultraviolet lamp
• pH meter

Correct Answer: Force transducer (isometric myograph)

Q29. Which practice helps minimize variability in biological assays?

• Standardize tissue source, temperature and use replicates
• Use different assay protocols for each replicate
• Randomly change buffer recipes during assay
• Avoid using reference standards altogether

Correct Answer: Standardize tissue source, temperature and use replicates

Q30. What regulatory requirement is crucial for bioassay methods used in potency testing?

• Method validation (accuracy, precision, specificity, linearity)
• Only visual inspection of raw data
• No documentation if performed in academic labs
• Exclusive reliance on historical results without revalidation

Correct Answer: Method validation (accuracy, precision, specificity, linearity)

G S Sachin

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.

Mail- Sachin@pharmacyfreak.com