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BIOAVAILABILITY:- It is defined as the rate and extent of absorption of active drug from its dosage form. Rate or rapidity with which a drug is absorbed is an imp consideration when a rapid onset of action is desired. eg :- In the treatment of asthama , pain. A slower absorption rate is desired when aim is to prolong the duration of action & to avoid the adverse effects. eg :- chronic condition – hypertension ,epilepsy. 3

Enhancement of bioavailability why????:

Enhancement of bioavailability why???? 4

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Poor aqueous solubility /dissolution rate In biological fluids. eg : nifidipine Poor permeability – lipophilicity /large molecular size. eg :-insulin. Poor drug stability of drugs. eg : gastric instability 5

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Bioavailability enhanced by Change the route of administration. ORAL PARENTERALS Modification of chemical structure. Disadv: Very expensive, time consuming, requires repetition of clinical studies and long time for regulatory approval, adv effects Pharmaceutical attempts - optimising the formulation, mfgprocess physico-chemical properties of the drug. Mainly aimed at altering the biopharmaceutical properties of drug. 7

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No major challenges for I.R forms, but CR forms need to limit drug release Formulations are designed to overcome dissolution problems Approaches are employed to enhance permeability Combination of stratagies are used for class II & class III Drugs BIOPHARMACEUTICS DRUG CLASSIFICATION SYSTEM

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Techniques used for the enhancing of drug solubility : Drug dispersion in carriers :- 1 .Use of eutectic mixtures 2.solid solutions Particle size reduction :- 1. supercritical fluid Recrystallization. 2. Spray Freezing into Liquid( SFL). 3. Evaporative Precipitation into Aqueous solution . Chemical modifications :- - Use of precipitate inhibitors. 10


SUPERCRITICAL FLUID RECRYSTALLIZATION SCFR is a novel nanosizing and solubilizing technology. Particle size reduction via supercritical fluid. eg:CO 2 –Tc-31 0 Pc-73 atm. Super critical fluid :-- fluids whose temperature and pressure are greater than its critical temperature &critical pressure. At near critical temp ,SCFs are highly compressible, and moderate changes in pressure to greatly alter the density and mass transport characteristics of fluid. 11

Supercritical fluid region:

Supercritical fluid region 12

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The SCF has both gas-like, liquid-like qualities. At the Tc & Pc the substance liquid and vapour phases are indistinguishable. SCFs offer liquid like –densities, gas like-viscosity, compressibility& higher diffusivity than the liquids. The scientist krukonis first used this technique to prepare 5-100nm particles of lovastatin . SCF technology useful for producing particles in the range of 5-2,000 nm. 13

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14 The drug is first dissolved in low boiling point organic solvent. This solution is pumped through a tube where it is heated under pressure to a temperature above the solvents boiling point and then sprayed through a fine atomizing nozzle in to a heated aqueous solution Surfactants are added to the aqueous solution. The surfactant migrates to the drug-water interface during particle formation , and the hydrophilic segment is oriented towards the aqueous continuous phase. This hydrophilic stabilizer on the surface facilitates dissolution rates. EVAPORATIVE PRECIPITATION INTO AQUEOUS SOLUTION (EPAS)

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DRUG (dissolved) Organic solvent Drug-organic mixture Spray into aq. solution Evaporation the organic solvent (presence of aq. solution). aq. dispersion of drug particle drug particle(nanometer-micrometer). 15

Solid solutions:

Solid solutions A Solid solution is formed when two metal are completely soluble in liquid state and solid state. Two components crystallize together in Homogenous one phase system, so solid solutions are also called as molecular dispersion. Because of reduction in particle size to molecular level ,solid solutions show greater aq solubility and faster dissolution than the eutectic mixtures. 16

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These are generally prepared by fusion method by physical mixture of solvent and solute are melted together followed by spfc solidification. eg :-griseofulvin- succinic acid The griseofulvin from such solid solution dissolves 6-7 times faster than pure griseofulvin. Solid solutions can be classified on two basis: 1.miscibility between the drug and carrier ; a. continous solid solution b. discontinous solid solutions. 17

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Distribution of drug in carrier structure :- a. Substitutional crystalline solid solution . In this drug molecules substitute for the carrier molecule in its crystal lattice. This happens when the size of drug and carrier molecules are almost of same size. b. Interstitial crystalline solid solution :- In this drug molecule occupy the interstitial spaces in the crystal lattice of carrier molecules. This happens when the size of drug molecule is 40%less than the carrier molecule. 18

Substitution solid solution Interstitial solid solution:

Substitution solid solution Interstitial solid solution 19


EUTECTIC SYSTEM Eutectic mixture:- It is a mixture of 2 or more chemical compound/elements/ phases,at a composition that has lowest melting point. 20

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A phase diagram represents a simple binary system composed of two components A&B which are varying in concentrations. The region labeled is alfa is solid solution.B acting as a solute in the mixture of A. Eutectic point is the point at which the liquid phase borders directly on solid phases (A&B). 22

Spray freezing into liquid:

Spray freezing into liquid 23 This technique involves atomizing an aqueous, organic, aqueous-organic co-solvent solution, aqueous organic emulsion or suspension containing a drug and pharmaceutical excipients directly into a compressed gas(co 2 , helium) or the cryogenic liquids ( i.e nitrogen, argon) The frozen particles are then lyophilized to obtain dry and free-flowing micronized powders

Schematic diagram of SFL using nitrogen as liquid cryogen:

Schematic diagram of SFL using nitrogen as liquid cryogen 24


Conclusion A drug administered in solution form immediately available for absorption. Solubility is a most important parameter for the oral bioavailability of poorly soluble drugs. Dissolution of drug is the rate determining step for oral absorption of the poorly water soluble drugs, which can subsequently affect the in vivo absorption of drug. Currently only 8% of new drug candidates have both high solubility and permeability. Because of solubility problem of many drugs the bioavailability of them gets affected and hence solubility enhancement becomes necessary. It is now possible that to increase the solubility of poorly soluble drugs with the help of these various techniques . 25


References D.M Brahmankar , SunilB.Jaiswal,Biopharmaceutics and pharmacokinetics A Treatise ,pg:no-349-355. Leon Lachman ; Herberta.Lieberman ; Joseph L.Kanig ,The Theory And Practise Of IndusPharmacy . 3 rd edition, Encyclopedia of pharma technology , AlfredMartin . Physical pharmacy , 4 th edition, 26

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Websites: . . . . . . 27

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