diffusion in biological systems-balu

Views:
 
Category: Education
     
 

Presentation Description

diffusion in biological systems

Comments

Presentation Transcript

Slide 1: 

P.BALA MURALI, 1ST M.PHARM(Pharmaceutics), 1st semester (2011-12)

Slide 2: 

It is defined as a process of mass transfer of individual molecules of a substance brought about by random molecular motion and associated with a driving force such as a concentration gradient. 23/01/2012 2 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 3: 

Diffusion of a drug across the biological membrane of a drug to be absorbed into and eliminated from the body and even for it to get to the site of action within a particular cell. Diffusion is time dependent process. Movement is based on kinetic energy(speed),charge and mass of molecules. 23/01/2012 3 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 4: 

Absorption, Distribution &Elimination of the drug biological membranes is by the diffusion. Release of drug from the dosage form. e.g.; sustained release, controlled release. Molecular weight of the polymers can be estimated. Absorption of the drugs can be studied. So many other processes follows the principle of diffusion. 23/01/2012 4 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 5: 

Diffusion can occur through the lipoidal by layer of the cells termed as “Transcellular diffusion”. Diffusion can occurs through the spaces between the adjacent cells termed as “Paracellular diffusion”. 23/01/2012 5 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 6: 

23/01/2012 6 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 7: 

Diffusion is a process of mass transfer of molecules of a substance from higher concentration to lower concentration Driving force of diffusion is concentration gradient. This process allows every molecule of a substance having higher concentration. Semi permeable membrane is absent Osmosis is a process of mass transfer of molecules of a substance from higher concentration to lower concentration through semi permeable membrane. Driving force of osmosis is osmotic pressure . This process doesn’t allows every molecule of a substance. Semi permeable membrane is present and has an orifice for drug release. 23/01/2012 7 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 8: 

Gastrointestinal absorption of drugs Percutanous absorption Buccal absorption Uterine diffusion 23/01/2012 8 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 9: 

Involves mainly simple diffusion due to differences in concentration gradient where gastro intestinal tract having higher concentration and systemic circulation having lower concentration. As we know many drugs are weakly acidic or basic, diffusion process depends upon a) Ionic character of drug b) Biological compartment c) Membranes HANDERSON HASSELBALCH Reaction for weak acid and weak base is as follows pH = pKa + log[Aˉ ]/ [HA] pH = pKa + log[B]/[BH] 23/01/2012 9 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 10: 

Percentage ionization of weak acid and weak base is given by % ionization = 100/1+antilog[pKa-pH] for weak acid. % ionization = 100/1+antilog[pH – pKa] for weak base. The drug absorption by diffusion through gastrointestinal pathway governed by a) state of ionization of drug b) solubility c) concentration in intestine d)membrane permeability 23/01/2012 10 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 11: 

pH PARTITION HYPOTHESIS “BRODIE” and his associates confirmed this theory. According to this theory This theory explains the drugs penetrate the biological membrane in their molecular and un disassociated form. Basis of this theory was that, the partition coefficient between membranes and gastrointestinal fluids is large hence the molecular form or undisassociated form enters from intestine and then to mucosal wall and finally into the systemic circulation. The disadvantages of this hypothesis is that it is partly applicable to biological membranes. Ex: Sulphathiazole. 23/01/2012 11 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 12: 

“Turner et al” suggested that the penetration of the drugs can be partly ionized or completely ionized which have the increased permeability ratios. This increase permeability ratio suggested that the penetration of ions are associated with sodium ion flux. The above passage involves the coupling of ions with sodium transport which passes the drug ions across the membrane. “Colaizzi” and “Klink” investigated the pH partition of behavior of Tetracyclines and found that lipid solubility and relative amount of ionic forms of tetracycline's at physiological pH(7.4) may have a barring on biological activity of various tetracycline used in clinical pharmacy . 23/01/2012 12 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 13: 

MODIFICATION OF pH PARTITION HYPOTHESIS “Higuchi” and his associates modified the pH partition hypothesis by taking considerations of so many factors and named it as “DULUISIO METHOD” . Metabolism of Drug in GI membrane. Absorption and secretion by carrier mediated process Absorption in micellar form Entero hetero hepatic circulatory effect . and given this below formula: Xs = 1/1+antilog[pH – pKa] 23/01/2012 13 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 14: 

Xs = 1/1+antilog[pH – pKa] where Xs = fraction of undissociated drug species. 23/01/2012 14 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 15: 

A. Transcellular B.Through channels between cells.C. Through sebaciuos glands. D. Transfillocular E. Through sweat glands 23/01/2012 15 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 16: 

According to “SCHEPLEIN” Percutaneous absorption involves 3 steps Dissolution of drug in vehicle. Diffusion of solubilised drug from vehicle to the surface of the skin. Penetration of drug through layers of skin. 23/01/2012 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS 16

Slide 17: 

23/01/2012 17 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 18: 

Factors influencing the penetration of drug through skin: Concentration of dissolved drug (Cs). Partition coefficient between skin and vehicle. Diffusion coefficient. Relative magnitude of these to coefficients. 23/01/2012 18 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Franz diffusion cell : 

Franz diffusion cell 23/01/2012 19 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 20: 

“Higuchi” and co workers mainly worked on diflorasone diacetate in propylene glycol – water and in poly oxy propyline 15 stearyl ether in mineral oil and proposed a diffusional equation for the system Where Cv = concentration of dissolved drug in the vehicle S = surface area of application Kvs = Skin vehicle partition coefficent of diflorasone diacetate Ds = diffusion coefficent of drug in skin V = volume of drug applied h = Thickness of skin barrier 23/01/2012 20 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 21: 

“Higuchi & his coworkers” also studied on to characterization of permeability suggest that certain proteins and lipid domains are responsible for the penetration of stratum corneum . Lipid content of stratum corneum is important to uptake the lipophilic drugs, but not hydrophilic drugs . 23/01/2012 21 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 22: 

The flux J here is where Cv = concentration of dissolved drug in the vehicle Kvs = Skin vehicle partition coefficient of diflorasone diacetate Okada et al carry out studies on vaginal absorption of hormones. 23/01/2012 22 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 23: 

“Beckett” and “Moffat” studied the diffusion of drugs into the lipid membranes of mouths in human based on pH-partion hypothesis , pKa , lipid water partition cofficent Ho and Higuchi applied this principle to analyse the buccal absorption of n –alkanoic acids which utilizes and known that only non ionized species pass across the lipid membrane. The reason that the buccal membrane does not posses significant aqueous pore path ways like intestinal membrane, and the surface pH is same as the buffered drug solution pH. 23/01/2012 23 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 24: 

This absorption follows first order process Where C = aqueous concentration of the n-alkanoic acid in the mucosal compartment. Ku = absorption rate constant which is given by This study shows an excellent correspondence between diffusional theory and in vivo absorption and suggests a fruit full approach for structural absorption. 23/01/2012 24 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 25: 

Drugs such as progesterone and contraceptives compounds are delivered in to the uterus by means of Intra Uterine Device (IUD)which is a diffusion controlled form. “Yotsuyanagi” performed in situ vaginal drug absorption studies and develop more effective uterine drug delivery systems. The drug will be implanted in the vagina in a silicone matrix and the drug delivery can be calculated using this expression. 23/01/2012 25 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 26: 

23/01/2012 26 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Contraceptive drug in water soluble silicone matrix : 

Contraceptive drug in water soluble silicone matrix 23/01/2012 27 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 28: 

“Diffusion is an important gateway by which many drugs are entering or eliminating and is a basis of many drug delivery systems” 23/01/2012 28 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 29: 

www.google.com www.wikipedia.com www.googleimage.com Martins Physical Pharmacy and Pharmaceutical Sciences,5TH edition, page no -315-326. 23/01/2012 29 DIFFUSION PRINCIPLES IN BIOLOGICAL SYSTEMS

Slide 30: 

23/01/2012 30

authorStream Live Help