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Modified-Release Drug Delivery Technology (Drugs and the Pharmaceutical Sciences) (Volume 2): Medicine & Health Science Books.
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Various systems are commercialized in market and available for patients for various diseases in which drug shows poor solubility e. The main advantage of this system is to overcome the drug solubility issue. This is the single osmotic unit or may combine with 5 to 6 push-pull units. Each system is 4mm in diameter, encapsulated within a hard gelatin capsule.

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This system is controlled by the surfactants and solubility modulating agent. The other advantages of this system is to provide a method for converting unacceptable drug release in vitro profiles that have been recognized as therapeutically desirable. Solubility modulation by Single unit drug delivery system is promptly fabrication to deliver a predetermined dose of agent at a programmed rate from compositions of matter in the varied geometries and sizes of tablets, pellets, multi-particulates, and such related dosage forms as familiar to those skilled in the art of oral, buccal, vaginal, rectal, nasal, ocular, aural and related routes of administration.

The particular composition having an active ingredient or a modulating agent, later agent should present within composition in such amount which is less than maximum concentration, which maintains saturation in medium that enter osmotic device. The above system utilise drug solubility. Organic, inorganic salts and solid inorganic acids are some example of modulating compounds. Osmotic System with expandable orifice is based on the structure of the capsule itself rather than the osmotic agent, solubility modifier and chemical composition placed in the capsule.

In this system, lag time depends on the structure of the capsular system. By forming the orifice in the wall section of the elastic material in osmotic system, creates the pulsatile release or initiate the drug release from the system through the orifice, which stretches in response to the osmotic pressure in system. The orifice is sufficiently small to remain closed, or at least considerably closed, when the pressure is less than the threshold level and yet opening as the elastic material stretches when the osmotic pressure rises to the threshold level Fig.

From the aqueous environment, capsule continuously absorbs the moisture; the absorbed moisture makes the pressure inside the capsule to rise until the level of threshold is achieved and at this time beneficial agent release from the orifice until the pressure is comfortably relieved to makes the orifice to reclose. This cycle is repeated until the beneficial agent is consumed from the system or the capsule is moved out from the environment. This system having one major advantage, which enhances the performance of the device, movable partition which divides the capsule interior into two compartments, one for osmotic engine and other for beneficial agent, which distinct from the beneficial agent.

Beneficial agent comprising the orifice at the capsular wall and during the travel, the partition will be at the beneficial agent. Osmotic agent compartment creates the pressure inside the capsule due to inward diffusion of water though the partition that keeps the contents of the two compartments from mixing. The multiplicity of small discrete units are combined in single oral dosage form are mainly called as Multiparticulate drug delivery system. Each discrete unit comprises of some specific characteristics.

Multiparticulate systems are divided into plurality of subunit of dosage, mostly containing thousands of spherical particles with the diameter of 0. So it is a multiparticulate dosage forms are pharmaceutical formulations in which the active substance is present as a number of small independent subunits. To provide optimum total dose, these system containing subunits that are packed into an encapsulated or sachet or compressed into a tablet. It provides many advantages as compared to single-unit system due to their small size subunits. Due to their better results such as increased bioavailability, reduced risk of systemic toxicity, reduced risk of local irritation and predictable gastric emptying are commonly a subject of development of multiparticulate dosage form instead of single unit systems.

These systems are also less dependent on the gastric emptying, ensuring less inter and intra parameter variance in gastrointestinal transit time.

Types of Oral controlled release devices

It shows better pharmacokinetic behaviour as compared to monolithic preparations. In modified multiparticulate pulsatile release system drug safety may also be increased.

MODIFIED RELEASE DRUG DELIVERY SYSTEM

For example, comparison between monolithic and multiparticulate, if the film coat of single unit in the case of monolithic is damaged, which leads to complete dose will be released in the stomach, which causes pain or ulceration or reduced efficacy, depending on the reason choosing the protection of the enteric coating. Similarly in the case of multiparticulate dosage form, especially for modified release system, if the film coated is damaged, which leads to the release characteristics are integrated into every single subunit, which represents a small part of the total dose and providing the safety to the dose.

Drug release mechanism from multiparticulate systems basically depends on three parameters such as diffusion, erosion and osmosis. Beside advantages, there are some disadvantages also such as low drug loading, proportionally higher need of excipients, large number of process variables and requirement of advanced technology, multiple formulation steps, adequate measure parameters, higher cost of production and skilled personnel to develop the formulations. Drug delivery system through altering membrane permeability in the formulation is based on the sigmoidal released pattern and it is beneficial for timed released and colonic drug delivery system.

Sigmoidal release pattern is established on the permeability and uptake of Eudragit RS or RL by water, regulated in the presence of dissimilar counter in the release medium. Narisawa et al. They observed that a very slow release rate of theophylline coated with Eudraget RS in pure water but when the microcapsules were impressed in acid solution such as glutaric, acetic, tartaric, malic and citric or succinic acid, a major increase in the release rate was observed.

This is because of the higher hydration of the film comprising quaternary ammonium groups on interaction with acids, was not affected by succinic acid. When succinic acid was in integrated into the core of Eudragit RS coated theophylline beads, the drug release profile showed a typical sigmoidal pattern.

In the case of acetaminophen contained product also showed the same results. Multiparticulate containing acetaminophen beads with different thickness of coating administered to beagle dogs and shows similar lag times in vivo and in vitro. Thickness of semipermeable decides the lag time; it is directly proportional to the thickness. Still, drug release profile was independent to the thickness but was affected by the amount of the salt in the system.

It is concluded that, release mechanism is dependent on the permeability modifier or amount of the salt. In this type of system coating ruptures or disintegrates to release a particular drug to the target. There are many reasons of rupturing of coat such as swelling, osmotic pressure, disintegration and effervescent recipient. In case of effervescent mixture which is usually contained in a mixture of citric acid and borax which is introduced into the core further coated with ethylcellouse.

Pressure is created inside the body of the system which leads to rupturing of the coating due to the generation of carbon dioxide gas in the system. Lag time in this system is dependent on the thickness of coating and hardness of the core tablet. Many agents such as sodium starch glycollate and low substituted hydroxyl propyl cellulose are used as the swelling agents and when they come in contact with the GI fluid, leads to the complete rupture of the film which leads to the drug release from the system.


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The Time clock system contained solid dosage form coated with lipid barrier such as carnauba wax and beeswax along with surfactants. When both these wax comes in interaction with aqueous medium, the coat emulsifies or erodes after the lag time. Viscosity grade and thickness of the polymer decides the lag time and onset action of the drug. In case of low density floating multiparticulate system, biological environment induce the stimuli to release the drug by the system.

Gels or micelles release the drug by the response from stimuli induced, which may deswell, swell or erode in the response to the respective stimuli. Biological factors such as temperature or other chemical stimuli induce the stimulation in the system and releases drug from it. Drug release mechanism is based on the ejection of the drug from the gel as the fluid phase syneresis out, drug diffusion along a concentration gradient, electrophoresis of charged drugs towards an oppositely charged electrode and liberation of the entrapped drug as the gel or micelle complex erode.

This system releases the therapeutic agents in the presence of specific enzyme or protein. Reason of choice of this system is that this can be qualified according to the task to be achieved and having excellent drug delivery system. Temperature play an important role to deliver the medicines in the system at a particular time and location.

The variation in the temperature act as triggers to stimulate the drug to target the disease accompanying fever, such type of system also known as thermosensitive Pulsatile drug delivery system. Mainly two type of systems work under the temperature induced system such as Thermoresponsive Hydrogel System and Thermoresponsive polymeric micelle system.

In Thermoresponsive Hydrogel System utilizes hydrogel which have reversible volume changes in reply to changes in temperature. Gel is made of liner polymer, which is follow at a transition temperature when gel shrinks at the lower critical solution temperature. Hydrogel have some specific characteristics to absorb the water from chemical attraction and swell at temperatures below the transition temperature whereas they shrink or deswell at temperature above the transition temperature by expelling water and in case of Thermo responsive Polymeric Micelle systems, due to its properties and biological interest, this is the best candidate as drug carrier for the treatment of cancer.

As the per the study of Kataoka and co-workers, it is observed that the polymeric micelle is build-up of amphiphilic block copolymers exhibiting a hydrophobic core with a hydrophilic corona, due to its unique characteristics, polymer micelles exhibit stealth characteristics and are not recognised by the body defence system reticuloendothelial system; RES. Thus, passive targeting could be accomplished through an enhanced permeation retention EPR effect of the tumour sites.

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Gels of this type of polymer display low viscosity at ambient temperature, and exhibit a sharp increase in viscosity as the temperature rises. Both systems are the best systems for Pulsatile Drug Delivery system when the medicament deliver through temperature induced system. In Chemical Stimuli Induced Pulsatile Release system, therapeutic agent release in the presence of any biological factor such as enzyme, pH or any other chemical stimuli.

These types of Pulsatile Drug Delivery system are used for diabetic patients for better compliance. This new approach to deliver an active drug in response to any stimulation that may be biological factor like enzyme, any endogenous substance.

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To supply insulin in the body is tedious job as it is different from other form of drugs. The glucose sensitive gel play a desperate role of self-controlling drug release in target tissue simultaneously regulating and separating system with glucose sensitivity.


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