in-vitro and in-vivo evaluation

Invitro and Invivo evaluation of buccal absorption: 

By:- Saiesh p. Phaldesai M.Pharma 1 st year Pharmaceutics Srinivas college of pharmacy mangalore Invitro and I nvivo evaluation of buccal absorption

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There are basicaly two important methods:- Invitro methods. Beaker Method. Modified Keshary Chien Cell. Invivo methods. Animals models Perfusion cell Absorption Cells Oh And Ritschel’s Buccal Absorption Test Rathbones Perfusion Cell Disc method

Invitro methods:: 

Invitro methods:

In Vitro Methods For Buccal Absorption: 

Animals are sacrificed immediately before the start of an experiment. Buccal mucosa with underlying connective tissue is surgically removed from the oral cavity, the connective tissue is then carefully removed and the buccal mucosal membrane is isolated. The membranes are then placed and stored in ice-cold (4°C) buffers (usually Krebs buffer) until mounted between side-by-side diffusion cells for the in vitro permeation experiments. How well the dissected tissue is preserved is an important issue, which will directly affect the results and conclusion of the studies. In Vitro Methods For Buccal Absorption

In Vivo Methods For Buccal Absorption: 

Animals models : used for the screening of a series of compounds, investigating the mechanisms and usefulness of permeation enhancers or evaluating a set of formulations. Dog, cat, rabbit, hamster, pigs, monkeys and sheep are used. dogs are much easier to maintain and their buccal mucosa is non-keratinized and has a close similarity to that of the human buccal mucosa. c In Vivo Methods For Buccal Absorption

Dosage Forms: 

Patches, adhesive film, bioadhesive tablets, non- bioadhesive tablets, ointments, aqueous solutions and gels. Buccal mucosa as a platform. Absorption characteristics of drug were assessed by measurement of amount of drug reaching blood or by removal and determination of the amount of drug remaining in the delivery system. Animals were immobilised and anesthetized throughout the experiment. Dosage Forms

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Perfusion cell :

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Other in vivo methods include those carried out using a small perfusion chamber attached to the upper lip of anesthetized dogs . The perfusion chamber is attached to the tissue by cyanoacrylate cement. The drug solution is circulated through the device for a predetermined period of time and sample fractions are then collected from the perfusion chamber (to determine the amount of drug remaining in the chamber) and blood samples are drawn after 0 and 30 minutes (to determine amount of drug absorbed across the mucosa).

Absorption Cells: 

Definition : Those techniques which restrict known volumes of an aqueous test solution to a defined surface of oral mucosa. Cell is protected from salivary secretions and does not change in volume. Test solution is not stirred during experiment. Absorption Cells

Ritschel’s Absorption Cell: 

Ritschel’s Absorption Cell

Zhang And Coworkers Absorption Cell: 

Zhang And Coworkers Absorption Cell

Yamahara et al Perfusion Cell: 

Yamahara et al Perfusion Cell

Photograph of four perfusion cells designed by Yamahara et al simultaneously attached to the buccal mucosa of dog: 

Photograph of four perfusion cells designed by Yamahara et al simultaneously attached to the buccal mucosa of dog

Absorption cell: 

The simplest absorption cell is a rubber ‘O’ ring with internal diameter 2.64 mm was fixed to the ventral surface of tongue of adult male Sprague Dawley rats using a cynanoacrylate adhesive. 10 ml of radiolabelled substance dissolved in a suitable buffer was placed into the ring and absorption characteristics determined by blood levels and test solution in ‘O’ ring. Absorption cell

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Buccal Absorption Test Using this method, the kinetics of drug absorption were measured. The methodology involves the : swirling of a 25 ml sample of the test solution for up to15 minutes by human volunteers followed by the expulsion of the solution. The amount of drug remaining in the expelled volume is then determined in order to assess the amount of drug absorbed.

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The drawbacks of this method include: salivary dilution of the drug, accidental swallowing of a portion of the sample solution, and the inability to localize the drug solution within a specific site ( buccal , sublingual, or gingival) of the oral cavity.

Disc Methods: 

Absorption across a defined oral cavity mucosa can be studied. Kaaber used a gravimetric method for measuring the uptake or loss of water using a small filter paper disc applied to the mucosal surface. Pimlot and Addy placed a drug soaked filter paper disc of known dimensions onto a defined oral mucosal surface. Maintained it for 5 min. After removal a non impregnated disc was used to wipe the oral mucosa, the disc combined, analyzed for drug content & the extent of drug disappearance is calculated. Disc Methods

Rathbones Perfusion Cell: 

Rathbones Perfusion Cell

Experimental Animal Species: 

Aside from the specific methodology employed to study buccal drug absorption/permeation characteristics, special attention is warranted to the choice of experimental animal species for such experiments. For in vivo investigations, many researchers have used small animals including rats and hamsters or permeability studies. However, such choices seriously limit the value of the data obtained since, unlike humans, most laboratory animals have an oral lining that is totally keratinized. Experimental Animal Species

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The rat has a buccal mucosa with a very thick, keratinized surface layer. The rabbit is the only laboratory rodent that has non-keratinized mucosal lining similar to human tissue and has been extensively utilized in experimental studies . The difficulty in using rabbit oral mucosa, however, is the sudden transition to keratinized tissue at the mucosal margins making it hard to isolate the desired non-keratinized region . The oral mucosa of larger experimental animals that has been used for permeability and drug delivery studies include monkeys , dogs and pigs . Due to the difficulties associated with maintenance of monkeys, they are not very practical models for buccal drug delivery applications. Instead, dogs are much easier to maintain and considerably less expensive than monkeys and their buccal mucosa is non-keratinized and has a close similarity to that of the human buccal mucosa.

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Pigs also have non-keratinized buccal mucosa similar to that of human and their inexpensive handling and maintenance costs make them an equally attractive animal model for buccal drug delivery studies. In fact, the oral mucosa of pigs resembles that of human more closely than any other animal in terms of structure and composition . However, for use in in vivo studies pigs are not as ideal as dogs due to their rapid growth which renders the animal handling rather difficult. Miniature breeds of pigs can be used but their high cost is a deterrent. For in vitro studies though, because of easy availability and low cost porcine tissue is more suited as compared to dog buccal tissue.

References:-: 

Novel drug delivery systems by Yie.W.Chien . pg:197-228. Controlled and novel drug delivery by N.K.Jain . pg:52-74. Indian journal of pharmaceutical sciences. www.google.com . www.elsevier.com References:-