Sustained Release Tablets Definition

Types of tablets in pharmaceutics

Conventional tablets: The main excipients are starch, dextrin, etc., which do not affect the disintegration and release of drugs, so ordinary tablets can be chewed, bitten, broken and taken.

Quick-release tablets: Designed to dissolve and release drugs quickly, they are used in emergency situations where effective blood concentrations need to be reached quickly.

Controlled release tablets: Tablets composed of high-tech matrix materials, penetration cores (containing drugs) and laser holes, etc., which release drugs at a slow and constant rate in a specified release medium. It is equivalent to dividing the entire drug into countless independent individuals, and releasing it separately and at a constant and controllable dose per unit time.

Sustained release tablets: Compared with traditional ordinary tablets, it has shown significant advantages in improving treatment effect, reducing side effects, and improving patient compliance.

Sustained release tablets

A sustained release tablet is a tablet designed to control the rate of drug release so that the drug is released slowly and continuously over a predetermined period of time. Different from the constant release of controlled release tablets, sustained release tablets release slowly and irregularly in the body after administration, and the absorbed drugs can maintain an effective blood concentration for a long time to achieve a long-term effect. The drug release generally conforms to the first-order kinetic process. The frequency of administration was reduced compared with that of ordinary preparations.

Sustained release technology delays the dissolution and absorption of drugs in the body through special preparation processes, such as coating, microencapsulation, and implantation of polymer matrix, so as to achieve the purpose of maintaining effective blood concentration for a long time.

Mechanism of sustained release tablets

The working principle of sustained-release tablets is based on a variety of mechanisms, including diffusion control, solution control, osmotic pressure drive and ion exchange.

Diffusion control: The drug is embedded in insoluble or slowly soluble carrier materials, through the drug molecules gradually diffuse into the surrounding medium to achieve release.

Dissolution control: The solvent excipients in the tablets gradually dissolve over time, driving drug release.

Osmotic pressure drive: The use of osmotic pressure difference to promote the water molecules into the inside of the preparation, promote the drug molecules to release.

Ion exchange: Suitable for preparations containing ionic drugs, through the ion exchange resin control drug release speed.

Diagrammatic representation of diffusion sustained drug release: matrix system. (Zalte, H. D., 2013)

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Advantages of sustained release tablets

• Less frequent drug administration
• Better patient compliance
• Less fluctuating blood drug levels
• Less overall drug use compared to conventional treatment
• Less drug accumulation with long-term therapy
• Reduction in systemic and local medication toxicity
• Stabilization of medical state (due to more consistent drug levels)
• Enhanced bioavailability of some drugs due to spatial control
• Economical for both the patient and the healthcare professionals

Types of sustained release tablets

Sustained release matrix tablets

Hydrophilic gel matrix tablets

This kind of tablet is made of hydrophilic polymer as the skeleton material, such as HPMC, methyl cellulose, sodium carboxymethyl cellulose and other cellulose derivatives, gelatin and other natural polymer compounds. The drug on the surface of the oral tablet quickly dissolves when it meets the digestive fluid, then the surface of the tablet is hydrated to form a gel, delaying the release of the drug: with the dissolution of the skeleton, the internal drug is slowly released as the digestive fluid permeates into the core of the tablet slowly diffuses to the surface.

Fat-wax matrix tablets

Various technique used for incorporation of drug into fat wax granulation which involve spray congealing in air, blend congealing in an aqueous media with or without the aid of surfactant and spray drying technique. Bulk congealing method, a suspension of drug and melted fat wax is allowed to solidify and then comminuted for sustained-release granulations. Mixing of active ingredients waxy materials and fillers when the mixing is over this mixture converted into granule by compacting with s compactor, heating in a suitable mixture such as fluidized-bed and steam jacketed blender or granulating with a solution of waxy material. The drug which is embedded into a melt of fats and wax released by leaching and hydrolysis as well as dissolution of fats under the influence of enzymes and pH change in the GI tract.

Coated sustained release tablets

Also known as film controlled sustained release tablets, refers to the use of one or more coating materials to coat the surface of the tablet, so that the drug is released slowly or at a constant rate through the coating film. Film control technology is the most common oral sustained release technology, which covers enteric film control, insoluble film control, semi-permeable film controlled release and a variety of film controlled release technologies, which can support the development of sustained release tablets and multi-particle pellets. The mechanism of drug release is that the membrane on both sides of the drug component forms a concentration difference in the liquid environment as the driving force of drug release. The drug release speed and release behavior can be controlled and adjusted by adjusting the coating film. Flim-controlled sustained-release preparations can increase the stability of drug preparations, improve the appearance of drugs and increase the recognition of drugs, reduce the stimulation of stimulant drug release on the human body at the same time, control the release speed of drug active ingredients and control the location and time of drug release, etc.

Osmotic pump sustained release tablets

The combination of film control technology and laser drilling technology, holes are punched in the coating film, and osmotic pressure is used as the drug release energy. The slow-release preparation of osmotic pump is generally composed of drug active ingredient, semi-permeable membrane material, osmotic pressure active substance and propelling agent. The mechanism of drug release is that the booster layer material absorbs water and expands, and the drug is slowly pushed out from the special drug release pore to achieve uniform and constant speed sustained drug release.

Single-chamber primary osmotic pump tablets

The drug is surrounded by a semi-permeable membrane material, the digestive fluid enters the osmotic system through the semi-permeable membrane, and the osmotic pressure active material produces an osmotic pressure difference, which makes the drug excreted. The saturated solution of the drug flows out of the pores of the tablet at a constant rate until the drug is completely dissolved in the tablet core.

Double-chamber osmotic pump tablets

The first layer of the core is composed of drugs, hydrophilic polymers with osmotic pressure activity and other excipients, which can be called drug-containing layer. The second layer of the core is composed of hydrophilic polymers, osmotic pressure promoters and other auxiliary materials, which can be called the booster layer. The core is coated with a semi-permeable film, and one or more drug release holes are opened on the two sides of the semi-permeable film, and the drug is connected with the external environment through the drug release holes. When the osmotic pump tablet enters the aqueous environment, the water enters the core through the drug release hole and the semi-permeable film, and the drug partially dissolves or hangs in the water under the action of the osmotic agent, and is released from the drug release hole under the action of osmotic pressure. In this system, the release rate is independent of the drug itself, and the drug release rate is controlled by controlling and adjusting the boost layer.

Sustained release tablets uses and example

Sustained release and controlled release technology has been widely used in clinical practice, covering the treatment of many diseases. For example, metformin hydrochloride sustained release tablets are used for blood glucose control, nifedipine controlled-release tablets are used for the treatment of cardiovascular diseases, carlevoba sustained-release tablets are used for the management of neurological diseases, and theophylline sustained-release tablets are used for the treatment of respiratory diseases.

Common insoluble matrix sustained release preparations include isosorbide mononitrate, diclofenac sodium and ibuprofen sustained release tablets.

Typical examples of soluble matrix sustained release tablets are morphine sulfate sustained release tablets and oxycodone hydrochloride controlled release tablets.

The controlled release formulations of multi-chamber osmotic pump include nifedipine sustained release tablets, doxazosin controlled release tablets and oxybutynin controlled release tablets.