Oral drug delivery remains the most preferred and convenient method for administering pharmaceuticals due to its ease of use, cost efficiency, and high patient compliance. Conventional tablets, despite their widespread use, often present challenges such as frequent dosing and fluctuating plasma drug concentrations, which can lead to reduced therapeutic efficacy and patient non-adherence. To address these issues, advanced drug delivery systems like sustained release tablets have been developed.

Sustained release tablets are designed to release the drug at a controlled and predictable rate over an extended period, maintaining consistent therapeutic drug levels and improving overall treatment outcomes. These systems reduce the need for frequent dosing, minimize side effects associated with peak drug concentrations, and enhance the convenience and compliance for patients managing chronic conditions like hypertension, diabetes, and arthritis.

Principles of Sustained Release Systems

The fundamental principle of sustained release drug delivery is to maintain a consistent plasma drug concentration within the therapeutic window over an extended period. Common drug release mechanisms include diffusion-controlled, erosion-controlled, and osmotic pressure systems.
Polymers play a critical role in controlling drug release. Hydrophilic polymers such as hydroxypropyl methylcellulose (HPMC) and hydrophobic polymers like ethyl cellulose are widely used.

Formulation Strategies

Matrix systems are simple and cost-effective formulations that incorporate hydrophilic or hydrophobic polymers to control drug release. Hydrophilic matrix systems use swellable polymers, while hydrophobic systems use insoluble materials to retard drug release.
Polymeric coatings on tablets or granules regulate drug release by creating a diffusion barrier. Osmotic systems rely on osmotic pressure to deliver drugs at a controlled rate. These systems are independent of pH and gastrointestinal motility.

Evaluation of Sustained Release Tablets

The performance of sustained release tablets is evaluated through various in vitro and in vivo methods to ensure safety, efficacy, and reproducibility.
In vitro evaluations include dissolution testing, drug content uniformity, and stability studies under accelerated conditions. In vivo evaluations involve pharmacokinetic studies and in vitro-in vivo correlation (IVIVC) to establish a link between in vitro release and in vivo performance.

Challenges and Future Perspectives

Despite their advantages, sustained release systems face challenges such as solubility issues, formulation complexity, and stringent regulatory requirements. Future directions include the use of biodegradable polymers, nanotechnology, and personalized medicine .

Sustained Release Tablet –