Controlled drug delivery systems integrate pharmaceutics, polymer science, and pharmacokinetics to deliver drugs at a predetermined rate, site, and duration. This introduction covers key terminology and the scientific rationale behind sustained release, controlled release, targeted delivery, matrix and reservoir systems, zero-order kinetics, diffusion-controlled and erosion-controlled mechanisms, burst release, rate-controlling membranes, osmotic pumps (OROS), biodegradable polymers (PLGA, PLA), mucoadhesion, therapeutic index, and release kinetics models (Higuchi, Korsmeyer–Peppas, Hixson–Crowell). Understanding these concepts helps B. Pharm students design formulations that improve bioavailability, reduce dosing frequency, and minimize side effects. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the best concise definition of a controlled drug delivery system?
- Systems that release drug slowly but unpredictably over time
- Systems designed to deliver a drug at a predetermined rate, for a specified period, and to a targeted location
- Any formulation that dissolves faster than conventional dosage forms
- Simple tablets coated to improve taste
Correct Answer: Systems designed to deliver a drug at a predetermined rate, for a specified period, and to a targeted location
Q2. How does a controlled release system differ from a sustained release system?
- Controlled release implies a predictable, often constant rate; sustained release merely prolongs drug release without strict rate control
- Sustained release systems always provide zero-order kinetics
- Controlled release systems release drug only once
- They are identical terms with no practical difference
Correct Answer: Controlled release implies a predictable, often constant rate; sustained release merely prolongs drug release without strict rate control
Q3. Which statement best describes zero-order release kinetics?
- Rate of drug release is proportional to the remaining drug concentration
- Constant amount of drug is released per unit time, independent of concentration
- Release rate decreases with the square root of time
- Release follows a logarithmic decline over time
Correct Answer: Constant amount of drug is released per unit time, independent of concentration
Q4. First-order release kinetics are characterized by which feature?
- Constant amount released per hour
- Release rate proportional to the remaining drug amount
- Release controlled exclusively by membrane erosion
- Zero release after initial burst
Correct Answer: Release rate proportional to the remaining drug amount
Q5. The Higuchi model describes drug release based on which mechanism?
- Surface erosion with constant geometry
- Diffusion from a homogenous matrix proportional to the square root of time
- Osmotic pumping through a semipermeable membrane
- Enzymatic degradation of polymer chains
Correct Answer: Diffusion from a homogenous matrix proportional to the square root of time
Q6. In the Korsmeyer–Peppas model, a release exponent (n) indicative of Fickian diffusion for a thin slab is approximately:
- n ≈ 1.5
- n ≈ 0.45
- n ≈ 2.0
- n ≈ 0.9
Correct Answer: n ≈ 0.45
Q7. What is the key structural difference between matrix and reservoir controlled systems?
- Matrix systems have a drug core surrounded by a membrane; reservoir systems disperse drug within polymer
- Matrix systems disperse drug in a polymeric matrix; reservoir systems have a drug core coated with a rate-controlling membrane
- Both are identical in design and function
- Reservoir systems always use biodegradable polymers while matrix systems do not
Correct Answer: Matrix systems disperse drug in a polymeric matrix; reservoir systems have a drug core coated with a rate-controlling membrane
Q8. What is meant by “burst release” in controlled delivery?
- Intentional delayed onset of drug release
- Rapid initial release of a significant fraction of drug immediately after administration
- Steady zero-order release throughout therapy
- Complete absence of drug release for a defined lag time
Correct Answer: Rapid initial release of a significant fraction of drug immediately after administration
Q9. The operating principle of an osmotic pump (e.g., OROS) is based primarily on:
- Diffusion through a rate-controlling polymer without solvent uptake
- Osmotic pressure generated by water influx through a semipermeable membrane driving drug out through an orifice
- Immediate dissolution and gastrointestinal absorption
- Enzymatic cleavage of a polymer backbone
Correct Answer: Osmotic pressure generated by water influx through a semipermeable membrane driving drug out through an orifice
Q10. What does the acronym OROS commonly represent?
- Orally Rapidly Osmotic System
- Osmotic (controlled) Release Oral System
- Organic Release Osmotic Suspension
- Osmotic Reactive Oral Solution
Correct Answer: Osmotic (controlled) Release Oral System
Q11. What is the primary function of a rate-controlling membrane in reservoir systems?
- To increase initial burst release
- To regulate drug diffusion and provide a predictable release rate
- To chemically react with the drug
- To rapidly degrade on contact with gastric fluid
Correct Answer: To regulate drug diffusion and provide a predictable release rate
Q12. Which clinical goal is central to controlled drug delivery?
- Achieve higher peak plasma concentrations regardless of toxicity
- Maintain plasma drug concentration within the therapeutic window for an extended period
- Maximize dosing frequency to increase patient contact
- Ensure drug only reaches the liver
Correct Answer: Maintain plasma drug concentration within the therapeutic window for an extended period
Q13. Which is a major patient-centered advantage of controlled release formulations?
- Increased dosing frequency
- Reduced dosing frequency and improved patient compliance
- Guaranteed cure of all chronic diseases
- Higher incidence of systemic side effects
Correct Answer: Reduced dosing frequency and improved patient compliance
Q14. Which of the following polymers are commonly used as biodegradable matrices in controlled release?
- PLGA, PLA, PCL
- Polyethylene glycol (PEG) only
- Sodium chloride and sucrose
- Starch solely as a non-degradable membrane
Correct Answer: PLGA, PLA, PCL
Q15. Mucoadhesive drug delivery systems are primarily designed to:
- Reduce drug absorption through mucosa
- Increase residence time at mucosal surfaces to enhance local or systemic uptake
- Ensure rapid gastric emptying
- Promote immediate drug elimination
Correct Answer: Increase residence time at mucosal surfaces to enhance local or systemic uptake
Q16. Which class of drugs most commonly benefits from controlled delivery due to narrow therapeutic range?
- Drugs with a very wide therapeutic index
- Narrow therapeutic index drugs (e.g., digoxin, lithium)
- Topical antiseptics
- Non-absorbed gastrointestinal agents
Correct Answer: Narrow therapeutic index drugs (e.g., digoxin, lithium)
Q17. Which factor does NOT typically influence drug release from a polymeric matrix?
- Polymer molecular weight and crystallinity
- Drug solubility and particle size
- Ambient light intensity (irrelevant unless photo-labile)
- Matrix porosity and tortuosity
Correct Answer: Ambient light intensity (irrelevant unless photo-labile)
Q18. How does erosion-controlled release differ from diffusion-controlled release?
- Erosion-controlled depends on polymer matrix degradation, while diffusion-controlled relies on drug diffusion through intact polymer
- They are identical mechanisms
- Diffusion-controlled requires enzymatic cleavage; erosion-controlled does not
- Erosion-controlled is always faster than diffusion-controlled
Correct Answer: Erosion-controlled depends on polymer matrix degradation, while diffusion-controlled relies on drug diffusion through intact polymer
Q19. Which route of administration is most commonly used to bypass hepatic first-pass metabolism for systemic controlled delivery?
- Transdermal
- Oral immediate-release tablet
- Enteric-coated oral tablet
- Rectal suppository that always undergoes full first-pass
Correct Answer: Transdermal
Q20. What is pulsatile drug delivery intended to achieve?
- Continuous zero-order release without fluctuation
- Drug release at specific programmed times to match circadian rhythms or disease needs
- Immediate burst release only
- Irregular unpredictable drug delivery
Correct Answer: Drug release at specific programmed times to match circadian rhythms or disease needs
Q21. Which of the following is an example of a depot formulation used for long-acting delivery?
- PLGA microsphere injectable suspension
- Immediate-release oral sugar-coated tablet
- Typical aqueous eye drops
- Uncoated capsule for fast disintegration
Correct Answer: PLGA microsphere injectable suspension
Q22. Which strategy is effective to reduce initial burst release from a reservoir system?
- Increase drug loading at the surface
- Apply an additional rate-controlling coating or lower surface drug concentration
- Create more pores in the membrane
- Use highly water-soluble polymers at the surface
Correct Answer: Apply an additional rate-controlling coating or lower surface drug concentration
Q23. Why is in vitro release testing crucial for controlled release formulations?
- It is irrelevant and rarely used
- It provides controlled conditions to predict in vivo behavior and ensure batch-to-batch consistency
- It always precisely replicates human pharmacokinetics
- It replaces the need for stability testing
Correct Answer: It provides controlled conditions to predict in vivo behavior and ensure batch-to-batch consistency
Q24. Compared to immediate-release forms, controlled release formulations generally aim to:
- Increase Cmax and shorten Tmax
- Reduce Cmax and prolong Tmax while maintaining therapeutic levels
- Eliminate therapeutic effect
- Cause rapid fluctuations in plasma concentration
Correct Answer: Reduce Cmax and prolong Tmax while maintaining therapeutic levels
Q25. How can controlled release improve the effective bioavailability of some drugs?
- By increasing peak concentrations far above toxic levels
- By reducing peak–trough fluctuations, optimizing absorption window, and minimizing pre-systemic metabolism
- By preventing any absorption
- By always converting drugs to inactive metabolites
Correct Answer: By reducing peak–trough fluctuations, optimizing absorption window, and minimizing pre-systemic metabolism
Q26. Increasing polymer crystallinity in a matrix is most likely to have which effect on drug release?
- Increase diffusion rate and speed up release
- Decrease diffusion rate and slow release due to reduced polymer free volume
- Eliminate the need for a rate-controlling membrane
- Cause immediate disintegration of the matrix
Correct Answer: Decrease diffusion rate and slow release due to reduced polymer free volume
Q27. A reservoir system containing an excess of solid drug core surrounded by a non-degradable membrane typically follows which kinetic profile?
- Higuchi square-root-of-time kinetics
- First-order kinetics dependent on remaining drug
- Zero-order kinetics as long as the core remains saturated
- Immediate complete release only
Correct Answer: Zero-order kinetics as long as the core remains saturated
Q28. What is the “therapeutic window”?
- The range between minimum effective concentration and minimum toxic concentration
- The time required for a drug to be eliminated
- A polymer property describing degradation rate
- The maximum solubility of a drug in water
Correct Answer: The range between minimum effective concentration and minimum toxic concentration
Q29. Which mathematical model accounts for changes in tablet surface area and diameter during dissolution (e.g., erosion or dissolution of solid particles)?
- Korsmeyer–Peppas model
- Higuchi model
- Hixson–Crowell cube-root law
- Michaelis–Menten kinetics
Correct Answer: Hixson–Crowell cube-root law
Q30. Which polymers are commonly used as water-insoluble rate-controlling materials in oral controlled release systems?
- Ethylcellulose, Eudragit RS/RL, and certain acrylic polymers
- Sucrose, lactose, and mannitol
- Sodium chloride and potassium chloride
- Gelatin and casein exclusively for insoluble membranes
Correct Answer: Ethylcellulose, Eudragit RS/RL, and certain acrylic polymers
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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