• Dissolution is a process in which a solid substance solubilizes in a given
solvent (mass transfer from the solid surface to the liquid phase.)
• Dissolution testing measures the extent and rate of solution formation
from a dosage form such as tablet, capsule, ointment, etc.
• The dissolution of drug is important for its bioavailability and therapeutic
• Dissolution can be defined as a physiochemical process by which a solid
substance enters the solvent phase to yield a solution or the transfer of
molecules or ions from a solid state into a solution.
4. • Dissolution rate is defined as the amount of solid substance goes into
solution per unit time under standard conditions of temperature, pH and
solvent composition and constant surface area.
• In the pharmaceutical industry, it may be defined as the amount of drug
substance that goes into solution per unit time under standardized
conditions of liquid/solid interface.
• Dissolution and drug release tests are in-vitro tests that measure the rate
and extent of dissolution or release of the drug substance from a drug
product, usually aqueous medium under specified conditions.
6. Factors relating to the dissolution apparatus
Design of the container
Size of the container
Shape of the container
Nature of agitation
Speed of agitation
Performance precision of the apparatus
7. METHODS FOR DISSOLUTION
There are basically three general categories of dissolution apparatus :
1. Beaker methods
2. Open flow-through compartment system
3. Dialysis concept
8. 1.BEAKER METHOD
• Rotating Basket Apparatus
• Rotating Paddle Apparatus
• The Reciprocating Cylinder Method
• Flow Through cell Apparatus
• Paddle over Disk method
• Cylinder method
• Reciprocating Holder method
9. • Rotating Basket Apparatus
It is basically a closed-compartment, beaker type apparatus.
It comprising of a cylindrical glass vessel with hemispherical bottom
of one litre capacity partially immersed in a water bath.
A cylindrical basket made of #22 mesh is located centrally in the
vessel at a distance of 2 cm from the bottom and rotated by a variable
speed motor through a shaft.
All metal parts like basket and shaft are made of stainless steel .
11. • Rotating Paddle Apparatus
In here, basket is replaced with a stirrer.
A small, loose, wire helix may be attached to the dosage form that
would otherwise float.
This method was first describe by levy and hayes.
The dosage form is allowed to sink in the bottom of the vessel
13. • The Reciprocating Cylinder Method
This apparatus consist of a set of cylindrical flat bottomed glass vessels
equipped with reciprocating cylinder.
The disks are not used.
This method is less suitable for precise dissolution testing due to the amount of
agitation and vibration involved.
E.g. Chlorpheniramine ER tablets, Carbamazepine chewable tablet
15. • Flow through cell Apparatus
The flow through apparatus consists of a reservoir for the dissolution medium
and a pump that forces dissolution medium through the cell holding the test
This apparatus is feasible for using large volume of dissolution fluid.
This apparatus feasibility for automation of apparatus.
This apparatus is ease of maintaining of sink conditions during dissolution
which is often required for drugs having limited aqueous solubility.
17. • Paddle over Disk method
In here, stainless steel disk designed for holding transdermal system
at the bottom of the vessel.
The disk/device should not sorb, react with, or interfere with the
specimen being tested.
The disk holds the system flat and is positioned such that the release
surface is parallel with the bottom of the paddle blade.
19. • Cylinder method
This apparatus is also used for evaluation of transdermal products
and is similar to rotating basket apparatus.
Temperature - 32 ± 0.5°
The dosage unit is placed on the cylinder.
Distance between the inside bottom of the vessel and cylinder is
maintained at 25 ± 2 mm
21. • Reciprocating Holder method
The assembly consists of a set of calibrated solution containers, a motor and
drive assembly to reciprocate the system vertically.
Various type of sample holder are used.
This apparatus is used for evaluation of transdermal products as well as non
disintegrating controlled release oral preparation.
The test is carried out at 32°C
23. Advantages of the Beaker Methods
The basket method is the most widely used procedure which confines the solid
dosage form to a limited area which is essential for better reproducibility.
It is advantageous for capsules as they tend to float at the surface thus
minimizing the area exposed to the dissolution fluid.
24. Limitation of the Beaker Methods
Clogging of the basket screen by gummy particles.
Tendency of the light particles to float.
Sensitivity of the apparatus to variables such as vibration, eccentricity, etc.
Rapid corrosion of the mesh in presence of HCl.
Sensitivity of the apparatus to any slight changes in the paddle orientation.
Non-reproducible position of the tablets at the bottom of the flask.
25. 2. OPEN FLOW-THROUGH COMPARTMENT SYSTEM
The dosage form is contained in a small vertical glass column with built in filter
through which a continuous flow of the dissolution medium is circulated
upward at a specific rate from an outside reservoir using centrifugal pump.
Dissolution fluid is collected in a separate reservoir.
E.g. lipid filled soft Gelatin capsule
No stirring and drug particles are exposed to homogeneous, laminar
flow that can be precisely controlled. All the problems of wobbling,
shaft eccentricity, vibration, stirrer position don’t exist.
There is no physical abrasion of solids.
Perfect sink conditions can be maintained
Tendency of the filter to clog because of the unidirectional flow.
Different types of pumps, such as peristaltic and centrifugal, have
been shown to give different dissolution results.
Temperature control is also much more difficult to achieve in column
type flow through system than in the conventional stirred vessel type.
29. 3.DIALYSIS SYSTEM
Here, dialysis membrane used as a selective barrier between fresh
solvent compartment and the cell compartment containing dosage
It can be used in case of very poorly soluble rugs and dosage form
such as ointments, creams and suspensions.
32. IN VITRO DRUG RELEASE TESTING
• Drug release is the process by which a drug leaves a drug product.
• In vitro drug release testing in rotating basket method:
In vitro release study was carried out by the rotating basket method.
Six tablets of each batch were taken and placed in rotating basket,
Then the rotating basket was introduced into 900 mL of each
dissolution medium (water, 0.1 M HCI and pH 6.8 phosphate buffer)
at 37°C 0.5°C with a rotation speed of 100 rpm..5 mL of sample
solution was collected at different time intervals (2, 4, 6, 8, 10, 12 h)
and filtered through hydrophilic membrane.
33. 5 mL of sample solution was collected at different time intervals (2, 4, 6, 8, 10,
12 h) and filtered through a 0.45 um hydrophilic membrane.
1.0 mL of subsequent filtrate was taken accurately to add into a 100 mL
volumetric flask and diluted with the corresponding dissolution medium to 100
mL and mixed well.
The amount of drug dissolved in the dissolution medium was measured using
an UV-visible spectrophotometer at 233 nm.
The same volume of fresh dissolution medium at the same temperature was
added to replace the amount withdrawn after each sampling.
The drug amount of cumulative release was calculated with a standard curve.
• D.M.Brahmankar, Biopharmaceutics and pharmacokinetics- A
Treatise; Vallabh Prakashan, page no-328-333
• Leon Shargel, Applied Biopharmaceutics & Pharmacokinetics; 4th
edition, page no- 429-435