JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Pharmacy IV NOVEL DRUG DELIVERY SYSTEMS Previous Question Paper (March-2021 - R17)

Controlled Drug Delivery Systems (CDDS) are designed to maintain drug concentration within the therapeutic window for a prolonged period. The advantages include improved patient compliance due to reduced dosing frequency, maintenance of steady-state plasma drug levels, reduction in total dose required, and minimized side effects by avoiding peak-trough fluctuations. Conversely, disadvantages include the high cost of development, potential for dose dumping, requirement for specialized manufacturing technologies, and the risk of toxicity if the system fails or is removed prematurely.

The fundamental principles governing CDDS are as follows:

1. Diffusion-controlled systems: These systems rely on the movement of drug molecules from a high concentration region to a low concentration region through a rate-controlling membrane or matrix. The rate of release is governed by Fick's first law of diffusion, where the flux is proportional to the concentration gradient across the barrier.
2. Dissolution-controlled systems: In these systems, the drug release is limited by the rate at which the drug or the carrier matrix dissolves in the surrounding medium. This is described by the Noyes-Whitney equation, where the dissolution rate depends on the surface area, diffusion coefficient, and the concentration gradient between the saturated layer and the bulk fluid.
3. Ion-exchange systems: These systems utilize water-insoluble cross-linked polymer resins containing ionizable groups. The drug is bound to the resin via ionic bonds. Upon ingestion, the drug is released through an exchange process with ions present in the gastrointestinal fluids (such as Na+, Cl-, or H+), where the drug ions are displaced by the counter-ions from the biological environment.

Polymers are fundamental components in drug delivery systems, categorized based on their solubility at specific pH levels. Enteric polymers are designed to resist gastric acid (pH 1-3) and dissolve in the higher pH environment of the small intestine, while non-enteric polymers typically dissolve or swell throughout the gastrointestinal tract.

Ideal Properties of Polymers:

• Biocompatibility and non-toxicity.
• Chemical stability and ease of processing.
• Appropriate mechanical strength and film-forming ability.
• Predictable and reproducible drug release characteristics.
• Low cost and regulatory acceptance (GRAS status).

Enteric Polymers:

These are pH-sensitive polymers containing acidic groups that remain unionized in the stomach but ionize at intestinal pH, leading to polymer dissolution.

Examples: Cellulose acetate phthalate (CAP), Hydroxypropyl methylcellulose phthalate (HPMCP), and Eudragit L/S series.

Advantages: Protect acid-labile drugs from gastric degradation, prevent gastric irritation by drugs, and enable targeted delivery to the small intestine.

Applications: Used for enteric coating of tablets and capsules, and for site-specific delivery in the duodenum or jejunum.

Non-Enteric Polymers:

These polymers are generally pH-independent or dissolve at lower pH levels, providing sustained or controlled release throughout the GI tract.

Examples: Hydroxypropyl methylcellulose (HPMC), Ethyl cellulose, and Polyvinyl pyrrolidone (PVP).

Advantages: Provide sustained release profiles, reduce dosing frequency, improve patient compliance, and minimize fluctuations in plasma drug concentration.

Applications: Used in matrix tablets, osmotic pump systems, and extended-release formulations to maintain therapeutic drug levels over prolonged periods.