Novel Drug Delivery Systems (NDDS) aim to improve drug therapeutic efficacy and safety by ensuring the timely delivery of the drug in required amounts to the target site.
Controlled release formulations, a type of NDDS, release the drug at a predetermined rate to maintain therapeutic drug concentrations over prolonged periods.
Principles of Controlled Release Formulations
A. Based on Diffusion
Diffusion-controlled systems rely on the movement of drug molecules from a region of higher concentration to one of lower concentration through a barrier or matrix.
Reservoir Systems:
Structure: Drug core surrounded by a polymeric membrane.
Mechanism: Drug diffuses through the membrane at a controlled rate.
Characteristics: Provides zero-order release kinetics; rate is independent of drug concentration.
Matrix Systems:
Structure: Drug dispersed uniformly within a polymer matrix.
Mechanism: Drug release occurs as it diffuses out of the matrix.
Characteristics: Release rate decreases over time; suitable for both hydrophilic and hydrophobic drugs.
B. Based on Dissolution
Dissolution-controlled systems regulate drug release through the dissolution of the drug or its coating.
Encapsulation Dissolution Systems:
Structure: Drug particles or granules coated with a slow-dissolving material.
Mechanism: Coating dissolves gradually, releasing the drug.
Characteristics: Can provide controlled release by varying coating thickness.
Matrix Dissolution Systems:
Structure: Drug embedded in a matrix of a dissolvable carrier.
Mechanism: Matrix dissolves slowly, liberating the drug.
Characteristics: Suitable for drugs with poor water solubility.
C. Based on Ion Exchange Principles
Ion-exchange systems utilize resins that bind ionic drugs, releasing them in exchange for ions in the gastrointestinal fluids.
Ion-Exchange Resins:
Structure: Insoluble polymers containing ionizable groups.
Mechanism: Drug-resin complexes exchange ions with GI fluids, releasing the drug.
Characteristics: Release rate depends on the ion concentration and pH of the environment.
Applications:
Taste Masking: Can mask unpleasant tastes of drugs.
Sustained Release: Provides prolonged drug action through controlled ion exchange.