Drug use measures: prescriptions, units dispensed, DDD, PDD MCQs With Answer

This blog provides an advanced multiple-choice question set on drug use measures—prescriptions, units dispensed, Defined Daily Dose (DDD) and Prescribed Daily Dose (PDD)—targeted to M.Pharm students studying Pharmacoepidemiology & Pharmacoeconomics. The questions explore definitions, calculation formulas, interpretation of consumption indicators, common pitfalls and practical applications in population and institutional settings. Emphasis is placed on converting product units to DDDs, computing DDDs per 1000 inhabitants per day, understanding PDD/DDD ratios, and recognizing limitations of standard metrics (for example in paediatrics or varying indications). Each MCQ reinforces analytical skills needed to evaluate drug utilization data and to compare consumption across time, regions, or healthcare providers.

Q1. What is the WHO-defined concept of Defined Daily Dose (DDD)?

• An assumed average maintenance dose per day for a drug’s main indication in adults
• The average dose actually taken by patients in a trial
• The maximum recommended dose listed in the product monograph
• The total amount of drug sold in a country in one year

Correct Answer: An assumed average maintenance dose per day for a drug’s main indication in adults

Q2. Which statement best describes Prescribed Daily Dose (PDD)?

• The theoretical dose used for cost calculations only
• The patient’s actual average daily dose as prescribed in a defined population
• The WHO standard dose applied worldwide for comparisons
• The total daily dose consumed by all patients in a year

Correct Answer: The patient’s actual average daily dose as prescribed in a defined population

Q3. “Units dispensed” in drug utilization studies most commonly refer to:

• The defined daily doses calculated from sales data
• Counts of physical dosage forms (tablets, capsules, vials) dispensed to patients
• The number of prescriptions written by a prescriber per month
• The number of treatment courses completed per 1000 inhabitants

Correct Answer: Counts of physical dosage forms (tablets, capsules, vials) dispensed to patients

Q4. Which formula correctly expresses DDDs per 1000 inhabitants per day?

• (Total amount of drug (mg) / WHO DDD (mg)) ÷ (population × number of days) × 1000
• (Number of prescriptions × DDD) ÷ population × 1000
• (Units dispensed ÷ population) × WHO DDD
• (Total mg dispensed ÷ population) × 365

Correct Answer: (Total amount of drug (mg) / WHO DDD (mg)) ÷ (population × number of days) × 1000

Q5. If total sales for a drug are 18,250 g over one year, the WHO DDD is 100 mg, and the population is 50,000, what is the DDDs per 1000 inhabitants per day?

• 1.0
• 5.0
• 10.0
• 20.0

Correct Answer: 10.0

Q6. A PDD/DDD ratio greater than 1.0 generally indicates:

• Prescribing below the recommended maintenance dose
• Prescribing average doses equal to WHO standards
• Prescribing higher-than-standard doses in the observed population
• That DDD is inappropriate and must be discarded

Correct Answer: Prescribing higher-than-standard doses in the observed population

Q7. Which is a key limitation of using DDD for pediatric drug utilization studies?

• DDD is too specific to a single manufacturer
• DDD does not reflect weight-based or age-specific dosing commonly used in children
• DDD overestimates adherence in adults
• DDD requires individual patient clinical data to compute

Correct Answer: DDD does not reflect weight-based or age-specific dosing commonly used in children

Q8. Converting “units dispensed” to total milligrams requires knowing:

• The number of prescriptions only
• The strength per unit and the number of units dispensed
• The daily consumption per patient only
• The WHO DDD for unrelated drugs

Correct Answer: The strength per unit and the number of units dispensed

Q9. Which indicator is most suitable for comparing drug consumption between two countries with different population sizes?

• Total units dispensed in each country
• Total sales value in local currency
• DDDs per 1000 inhabitants per day
• Number of marketing authorizations issued

Correct Answer: DDDs per 1000 inhabitants per day

Q10. How do you calculate the total number of DDDs from dispensed units?

• Total DDDs = Number of units × strength per unit (mg) ÷ WHO DDD (mg)
• Total DDDs = Number of prescriptions × population
• Total DDDs = Units dispensed × DDD per 1000 inhabitants
• Total DDDs = Number of patients treated ÷ WHO DDD

Correct Answer: Total DDDs = Number of units × strength per unit (mg) ÷ WHO DDD (mg)

Q11. If 10,000 tablets of 20 mg are dispensed and WHO DDD is 40 mg, how many DDDs does this represent?

• 2,500 DDDs
• 5,000 DDDs
• 10,000 DDDs
• 20,000 DDDs

Correct Answer: 5,000 DDDs

Q12. Which metric best reflects the average prescribed dose in a specific patient population rather than a standardized global benchmark?

• Defined Daily Dose (DDD)
• Prescribed Daily Dose (PDD)
• Units dispensed per pharmacy
• Wholesale sales in defined monetary units

Correct Answer: Prescribed Daily Dose (PDD)

Q13. A study reports 15 DDDs/1000 inhabitants/day for an antibiotic in Region A and 30 DDDs/1000 inhabitants/day in Region B. Which interpretation is most appropriate?

• Region B necessarily has twice the number of treated patients as Region A
• Region B shows higher population-level antibiotic consumption, but differences may reflect prescribing patterns or indication mix
• Region A prescribes higher doses per patient than Region B
• Region A has poorer adherence than Region B

Correct Answer: Region B shows higher population-level antibiotic consumption, but differences may reflect prescribing patterns or indication mix

Q14. Why can “units dispensed” be misleading when comparing use of two drugs with different strengths and formulations?

• Units dispensed are always lower than DDDs
• Units do not capture active substance quantity per unit, so they cannot be equated across strengths/formulations
• Units dispensed already account for DDD and PDD differences
• Units dispensed are normalized per 1000 inhabitants by default

Correct Answer: Units do not capture active substance quantity per unit, so they cannot be equated across strengths/formulations

Q15. Which measure is commonly used to express inpatient antibiotic use standardized to hospital activity?

• DDDs per 100 bed-days
• Units dispensed per prescription
• PDD per outpatient visit
• Total sales per hospital

Correct Answer: DDDs per 100 bed-days

Q16. When converting prescription counts into population-level indicators, the denominator selection is critical. Which denominator is typically used for DDDs per 1000 inhabitants per day?

• Number of prescribers in the region
• Population size and number of days in the period studied
• Number of pharmacies dispensing the drug
• Total number of marketed drug products

Correct Answer: Population size and number of days in the period studied

Q17. Which advantage is attributed to using DDD as a metric in pharmacoepidemiology?

• It perfectly reflects individual patient dosing decisions
• It provides a standardized metric to compare drug consumption over time and between populations
• It eliminates the need to know drug strength or formulation
• It indicates clinical appropriateness of prescribing for each patient

Correct Answer: It provides a standardized metric to compare drug consumption over time and between populations

Q18. For monitoring adherence at the individual patient level, which measure is more directly informative?

• DDDs per 1000 inhabitants per day
• Units dispensed and refill intervals
• National sales figures in defined daily doses
• WHO-assigned DDD values alone

Correct Answer: Units dispensed and refill intervals

Q19. Which of the following best describes a situation where PDD < DDD?

• Patients are on average prescribed lower daily doses than the WHO assumed maintenance dose
• Drug sales data are overestimated due to packaging
• The drug cannot be quantified using DDD methodology
• Population-level consumption must be higher than expected

Correct Answer: Patients are on average prescribed lower daily doses than the WHO assumed maintenance dose

Q20. When preparing a comparative drug utilization report between two hospitals, which steps ensure valid interpretation of DDD-based indicators?

• Use raw units dispensed without adjustment and ignore patient case-mix
• Standardize to bed-days or population denominator, account for case-mix and differences in indication, and check PDD/DDD ratios
• Compare only the number of prescriptions written by each hospital’s lead physician
• Rely solely on wholesale sales value in local currency for comparison

Correct Answer: Standardize to bed-days or population denominator, account for case-mix and differences in indication, and check PDD/DDD ratios

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