Site Specific Drug Delivery System-By $atyajit

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Site specific drug delivery : 

Site specific drug delivery By, Mr. $atyajit S. Deshmukh - M. Pharm

Contents : 

Contents Drug delivery to colon Drug delivery to brain Formulation of parenterals Freeze drying of parenterals Conclusion References

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ANATOMY OF COLON » Ascending Colon » Transverse colon » Descending Colon » Sigmoid Colon Mucosa Submucosa Muscularis externa Serosa

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Colon as a Site for Drug Delivery • Most of the drugs are absorbed from upper part of the GI tract as compared to colon. • Promising site for drug delivery » Local disorders » Systemic absorption » Drugs unstable in upper GIT » Drugs poorly absorbed from GIT » Drugs that necessitate targeting at site

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Rationale for the Development of Colon Targeted Drug Delivery » Treatment of local pathologies » Chronotherapy (asthma, hypertension, cardiac arrhythmias, arthritis or inflammation ) » Greater responsiveness to the absorption enhancers. » Less enzymatic activity » Site for delivery of delicate drugs (Proteins and Peptides).

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Pharmaceutical Approaches for Targeting Drugs to Colon » PH sensitive system » Microbially triggered systems » Prodrugs Polysaccharide based systems Time release systems » Osmotically controlled drug delivery systems » Pressure dependent release systems

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PH sensitive systems

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Mechanism of action of a PH dependent system for targeted drug delivery to the colon PH sensitive polymer + drug core DRUG CORE Colonic pH Release of drug in Colon

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Polymer of methacrylic acid are mostly used

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Microbially Triggered Systems » Bacterial count in the colon is much higher around 1010- 1011 CFU/ml. » 400 species » Fundamentally anaerobic in nature. » Predominant species: Bacteroides, Bifidobacterium and Eubacterium. » Major metabolic processes occurring in the colon are hydrolysis and reduction.

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Colonic Microflora Human intestinal microflora distribution in number (Log 10 scale) per gram faeces.

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Reducing enzymes » Nitroreductase » Azoreductase » N-oxide reductase » Sulphoxide reductase » Hydrogenase Hydrolytic enzymes » Esterases » Amidases » Glycosidases » Glucuronidase » Sulfatase » Azoreductases: which reduces azo-bonds selectively and » Polysaccharidases: which degrades the polysaccharides. Enzymes in Colon

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Bacteria in colon Hydrolysis of sulphasalazine (A) into 5-aminosalicylic acid (B) and sulfapyridine (C). (A) (B) (C)

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Prodrugs Drug Carrier Molecule Enzymatic stimuli in the biological environment of the colon breaks the bond Concept of prodrugs

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Natural Polysaccharides as Polymer for Colon Drug Delivery » Inulin » Guar gum » Pectin » Almond gum » Locust bean gum » Khaya gum » Boswellia gum » Chitosan » Chondroitin sulphate » Dextran » Cyclodextrins

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Enteric coated matrix tablet Enteric coated matrix tablet in upper GI Solublization of enteric coat and swelling of inner matrix followed by degradation by colonic bacteria Degradation of swelled matrix tablet and drug release Behavior of Enteric-coated Polysaccharide Matrix Colonic bacteria

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Intact compression coated tablet Swelling of coat in upper GI Environment Swelled coat Degraded by colonic bacterial enzymes Degradation of coat and drug release Compression Coated Tablets Colonic bacteria

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Timed Release Systems » Releases the drug after a predetermined lag time » The lag time usually starts after gastric emptying because most of the time-controlled formulations are enteric coated. » Drug release from these systems is not PH dependent

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Osmotically Controlled Drug Delivery Systems Delivery port Rigid semi permeable membrane Osmotic agent layer Fluid to be pumped Depend up on the osmotic pressure exerted by osmogen on drug compartment with which though drug get released slowly though the orifice.

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» PULSINCAP » OROS-CT Advanced Technologies for CTDDS Pressure Dependent Release Systems Relies on the relatively strong peristaltic waves in the colon that lead to an increased luminal pressure, in response to raised pressure of the colon the dosage form get ruptured and release the drug at desired site

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THE FLUID-BRAIN BARRIERS These are the group of cells that inhibit passage of non-lipid soluble molecules from external environment of CNS to internal environment of CNS. The BBB associated with capillary, venule, and arteriole endothelia of cerebral blood vessels. The blood cerebrospinal fluid (CSF) barriers associated with epithelia of the choroid plexus and other cerebroventricular organs. The nose brain barrier associated with epithelia of the nasal mucosa. The arachnoid mater-CSF barrier.


FACTORS AFFECTING DRUG PERMEAATION THROUGH BBB The time dependent plasma concentration profile The permeability of the BBB to the agent Local cerebral blood flow. Elimination from the systemic circulation. Plasma protein binding Diffusion in the brain ISF

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Transport through BBB: 1.Carrier mediated system. Peptide transport system (PTS). e.g. Tyr-Pro-Leu-Gly-amide, methionine, enkephaline, orginine, vassopressin. 2. Receptor mediated transport (RMT). e.g. Peptides- Insulin, transferrin, growth factor. 3. Absorptive mediated transport (AMT) e.g. Proteins like albumin, histone, avidine

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Mechanism Of Drug Transport Through BBB

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STRATEGIES FOR BRAIN DELIVERY OF DRUG NEUROSURGICAL PHARMACOLOGIC PHYSIOLOGIC BBB disruption Intra-Ventricularinfusion Nano-particles Chemical delivery system Liposomes Pseudo- nutrients Chimeric peptides e.g. Dihydropyridine-Pyridinium salt with Dopamine drug L-Dopamine transported by neutral amino acid carrier

Formulation of parenterals: : 

Formulation of parenterals: Different Excipient used in formulation of parenterals are-

Freeze drying of parenterals: : 

Freeze drying of parenterals: Parenteral formulation (Solution form) Sterile solid formulation It is yhe process which is carried at temperature &pressure less than tripple point of water [ Tripple point – 0.00980C, 4.58mmHg pressure] It is mainly used for parenteral system which contains the heat sensitive material.

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The lyophilization process includes- Dissolving the drug and excipients in a suitable solvent. Sterilizing it by passing it through a 0.22 micron filter. Filling into sterile containers and partially stoppering the containers. Transporting the containers to the lyophilizer chamber under aseptic condition. Freezing the solution. Applying a vacuum to the chamber. Heating the shelves in order to evaporate the water from the frozen state. Vials with sterile solid formulation.

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Freeze -drier

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Advantages: Ease of processing a liquid, which simplifies aseptic handling Enhanced stability of a dry powder Removal of water without excessive heating of the product Enhanced product stability in a dry state Rapid and easy dissolution of reconstituted product. Disadvantages: Need for sterile diluent for reconstitution Cost and complexity of equipment.

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References: S.P. Vyas and R.K. Khar, Targeted and controlled drug delivery Novel carrier system by CBS publisher and distributers, Page no. 497-512. N. K. Jain, “Advances in Controlled & Novel Drug Delivery”, First edition-2001, CBS Publishers & Distributors, Pharmabiz, InterphexIndia and IPA convention-2007, Saffron media publication, September13,2007 Page No.96 (Mechanism of transport across BBB). Lieberman and Leon Lachman, Pharmaceutical dosage form Parenteral medication volume II, Page no. 163-235, 411-473. (freeze drying and parenteral environmental control.)

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Thank You

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