Dosage Lec - Module 5

Modified Release Dosage Forms

Dosage forms designed to release drug at a predetermined rate, duration, or site to achieve therapeutic goals

Conventional Dosage Forms

Release drug immediately after administration; may require multiple daily doses

Advantages of Modified Release

Improved patient compliance, reduced dosing frequency, sustained therapeutic effect, minimized side effects

Disadvantages of Modified Release

Costly, complex manufacturing, dose dumping risk, not suitable for all drugs

Types of Modified Release Dosage Forms

(1) Sustained release → (2) Controlled release → (3) Delayed release → (4) Targeted release

Sustained Release

Release drug slowly over extended period to maintain plasma concentration

Controlled Release

Release drug at a constant rate for prolonged time

Delayed Release

Release drug at a later time after administration (e.g., enteric-coated tablets)

Targeted Release

Drug release directed at specific site of absorption or action

Mechanisms of Modified Release

(1) Diffusion-controlled → (2) Dissolution-controlled → (3) Osmotic systems → (4) Ion-exchange systems

Diffusion-Controlled Release

Drug diffuses through polymer matrix or membrane at controlled rate

Dissolution-Controlled Release

Drug release depends on dissolution rate of polymer or coating

Osmotic System

Drug release controlled by osmotic pressure through semipermeable membrane

Ion-Exchange System

Drug release through interaction with ion-exchange resins

Polymers in Modified Release

Natural (cellulose derivatives), synthetic (polyvinylpyrrolidone, polymethacrylates), biodegradable polymers

Hydrophilic Matrix Systems

Swelling polymers form gel barrier that controls drug release

Hydrophobic Matrix Systems

Insoluble polymers control drug diffusion

Reservoir Systems

Drug core surrounded by polymer coating; release controlled by diffusion

Enteric-Coated Dosage Forms

Coated with polymer to resist gastric fluid but dissolve in intestinal fluid

Purpose of Enteric Coating

Protect drug from gastric acid, protect stomach from irritation, delay release until intestine

Polymers for Enteric Coating

Cellulose acetate phthalate, hydroxypropyl methylcellulose phthalate, methacrylic acid copolymers

Evaluation of Modified Release Dosage Forms

In vitro dissolution, drug release kinetics, stability, uniformity, bioavailability studies