The document discusses in vitro and in vivo methods for evaluating oral mucosal drug delivery systems. It describes methods such as residence time testing using a disintegration apparatus, in vitro mucoadhesion tests using a universal testing machine, and permeability studies using animal buccal tissue or epithelial cell cultures. Robust in vitro methods are needed to assess performance of these systems and predict their in vivo behavior in order to establish correlations between in vitro and in vivo results.

1. In vitro and in vivo evaluations of
oral mucosal drug delivery systems
R & D Centre,
Transdermal and film dosage form,
Hetero Healthcare Limited,
Jeedimetla, Hyderabad.
Shrikant Sadashivrao Patil, PhD

2. Introduction:
Drug delivery within the oral cavity;
a) Sublingual mucosa b) Buccal mucosa
The delivery of drugs through oral mucosa has attracted much research
interest because; it is more fitted for sustained delivery applications,
delivery of less permeable molecules and perhaps peptide drugs.
Major disadvantage of oral mucosal drug delivery is low flux which
results in low drug bioavailability.

3. Structure of the oral mucosa:
The oral mucosa is composed of an outermost layer of stratified squamous
epithelium. Below this lies a basement membrane having lymphocytes and
blood vessels followed by the submucosa as the innermost layer.
Figure 1. Structure of the oral mucosae

4. In vitro assessment of mucosal delivery systems
1) Disintegration test
2) Dissolution studies
3) Residence time
4) In vitro muco-adhesion tests
5) Permeability studies
a) Animal buccal tissue
b) Buccal epithelial cell cultures

5. In vitro assessment of mucosal delivery systems
1) Residence time: In vitro residence time test is useful to evaluate the
performance of muco-adhesive drug delivery systems intended to
remain at the site of application to enable prolonged drug release.
Figure 2. Schematic diagram of the apparatus used for the
determination of residence time.
It can be measured using modified
disintegration apparatus as shown in
figure 2.
It is the time necessary for complete
erosion or detachment of the dosage
form from the mucosal surface .

6. 1) Residence time experiment:
• Take DT apparatus and set temperature as 37ºC of water bath.
• Add 500 mL of DT medium (Phosphate buffer with pH 6.8) to it.
• Equilibrate the system to attain 37ºC of medium temperature.
• Take a glass slide and cover the mucosa on it. Attach this slide with
mucosa vertically as shown in figure 2.
• Hydrate the film surface and bring it in contact with above slide.
• Immerse the film applied slide in to the DT medium to up and down.
• Record the time required for complete erosion or detachment of the
film from the mucosal surface in minutes or hours.

7. 2) In vitro muco-adhesion tests:
- The most obvious method to assess the muco-adhesive strength of the
dosage forms is through the determination of the adhesive strength
between polymer and the attached substrate. (membrane / mucosa)
- The adhesive strength at such a bonding interface can be measured by
evaluating the force required to detach one entity from the other through
the application of an external force.
- As such the destruction of the adhesive bond usually occurs under the
application of either a shearing, tensile or peeling force. Universal testing
machine can be used to estimate adhesion between film and mucosa.

8. 3) Permeability studies by using animal mucosa:
- Drug permeability studies are usually employed to determine the barrier
nature of different biological tissues whereby the diffusion of drugs can be
studied in a controlled environment in which variables such as
temperature, pH and osmolarity can be easily controlled.
- Human buccal tissues may be the most useful to mimic the real in vivo
situation but because of their limited availability use of animal tissue is
preferable. However, such data should be treated with caution because of
the differences observed between human and animal buccal mucosa.
Human mucosa : Non-keratinized, membrane thickness 580 ± 90 µm
Pig mucosa : Non-keratinized, membrane thickness 772 ± 150

9. Permeability studies by using animal mucosa:
-The most widely used in vitro methodology to study oral mucosal
permeability is by testing drug permeation across isolated mucosal tissue
mounted in permeability chambers.
-The use of diffusion cells makes it possible to determine the actual amount
of drug that diffuses across the mucosal barrier as well as the rate of drug
diffusion.
-Most commonly two types of permeability cells have been used:
(a) Vertical Franz diffusion cell (b) Side-by-side horizontal cell.
-In permeability studies synthetic membranes made up of nylon, PTFE and
PVDF also used.

10. Permeability studies by using epithelial cell cultures:
- This technology has been used because drawback of animal tissues
maintenance, viability and integrity.
- In this; mucosa cells are cultured and grown. The barrier nature of this
cell culture model is similar to intact buccal mucosa.
- Recently a new cultured human buccal epithelium model, EpiOral™, has
become commercially available (MatTek, Ashland, MA, USA). This tissue
model consists of normal human keratinocytes cultured to form a three-
dimensional differentiated tissue that histologically and biochemically
resembles human buccal tissue.
Limitation: Variation in drug release due to non control of culture growth.

11. Summary
 Robust and validated in vitro and in vivo methods are essential tools
to assess the performance of oral mucosal drug delivery systems and
to predict their in vivo behaviour.
 By using such methods; correlation between in vitro and in vivo
(IVIVC) can be predicted in order to reduces the product
development cost and can saves time.
 A good correlation is a tool for predicting in vivo results based on in
vitro data and it allows dosage form optimization with the fewest
possible trials in man, fixes drug release acceptance criteria, and can
be used as a surrogate for further bioequivalence studies.