As per USP Guideline,
Dissolution is the process in which a substance forms a solution. Dissolution testing measures the extent and rate of solution formation from a dosage form, such as tablet, capsule, ointment, etc. The dissolution of a drug is important for its bioavailability and therapeutic effectiveness.
A dissolution test uses an apparatus with specific test
conditions in combination with acceptance criteria to evaluate the performance
of the product. General chapter <711> Dissolution includes 4 standardized
apparatus: basket, paddle, reciprocating cylinder, and flow-through cell.
Apparatus 1 (Basket)
The assembly (Apparatus 1) consists
of the following: a vessel, which may be covered, and made of glass or other
inert, transparent material; a motor; a metallic drive shaft; and a cylindrical
basket. The vessel is partially immersed in a suitable water bath of any
convenient size or heated by a suitable device, such as a heating jacket. The
water bath or heating device permits holding the temperature inside the vessel
at 37 ± 0.5°C during the test and keeps the bath fluid in constant, smooth
motion.
No part of the assembly,
including the environment in which the assembly is placed, contributes significant
motion, agitation, or vibration beyond that due to the smoothly rotating,
stirring element. An apparatus that permits observation of the specimen and of
the stirring element during the test is preferable. The vessel is cylindrical,
with a hemispherical bottom and with one of the following dimensions and
capacities: for a nominal capacity of 1 L, the height is 160–210 mm, and its
inside diameter is 98–106 mm; for a nominal capacity of 2 L, the height is
280–300 mm, and its inside diameter is 98–106 mm; and for a nominal capacity of
4 L, the height is 280–300 mm, and its inside diameter is 145–155 mm . Its
sides are flanged at the top. A fitted cover may be used to retard evaporation.
The shaft is positioned so that
its axis is not more than 2 mm at any point from the vertical axis of the
vessel and rotates smoothly and without significant wobble that could affect
the results. A speed-regulating device is used that allows the shaft rotation
speed to be selected and maintained at the specified rate given in the
individual monograph within ±4%.
Shaft and basket components of the stirring element are
fabricated of stainless steel, type 316, or other inert material, to the
specifications. A basket having a gold coating of about 0.0001 inch (2.5 µm)
thick may be used. A dosage unit is placed in a dry basket at the beginning of
each test. The distance between the inside bottom of the vessel and the bottom
of the basket is maintained at 25 ± 2 mm during the test.
Apparatus 2 (Paddle)
Use the assembly from Apparatus
1, except that a paddle formed from a blade and a shaft is used as the stirring
element. The shaft is positioned so that its axis is not more than 2 mm from
the vertical axis of the vessel at any point and rotates smoothly without
significant wobble that could affect the results. The vertical center line of
the blade passes through the axis of the shaft so that the bottom of the blade
is flush with the bottom of the shaft. The paddle conforms to the
specifications shown below. The distance of 25 ± 2 mm between the bottom of the
blade and the inside bottom of the vessel is maintained during the test.
The metallic or suitably inert,
rigid blade and shaft compose a single entity. A suitable two-part, detachable
design may be used, provided that the assembly remains firmly engaged during
the test. The paddle blade and shaft may be coated with a suitable coating so
as to make both of them inert. The dosage unit is allowed to sink to the bottom
of the vessel before rotation of the blade is started. A small, loose piece of
nonreactive material, such as not more than a few turns of wire helix, may be
attached to dosage units that would otherwise float. Other validated sinker
devices may be used.
Apparatus 3 (Reciprocating Cylinder)
The assembly consists of a set of
cylindrical, flat-bottomed glass vessels; a set of glass reciprocating
cylinders; inert fittings (stainless steel type 316 or other suitable
material), and screens that are made of suitable nonsorbing and nonreactive material
and that are designed to fit the tops and bottoms of the reciprocating
cylinders; and a motor and drive assembly to reciprocate the cylinders
vertically inside the vessels; if desired, index the reciprocating cylinders
horizontally to a different row of vessels.
The vessels are partially
immersed in a suitable water bath of any convenient size that permits holding
the temperature at 37 ± 0.5°C during the test. No part of the assembly,
including the environment in which the assembly is placed, contributes
significant motion, agitation, or vibration beyond that due to the smooth,
vertically reciprocating cylinder. A device is used that allows the
reciprocation rate to be selected and maintained at the specified dip rate
given in the individual monograph within ±5%. An apparatus that permits observation
of the specimens and reciprocating cylinders is preferable. The vessels are
provided with evaporation caps that remain in place for the duration of the
test. The components conform to the dimensions shown below, unless otherwise
specified in the individual monograph.
Apparatus 4 (Flow-Through Cell)
The assembly consists of a reservoir and a pump for the
Dissolution medium; a §ow-through cell; and a water bath that maintains the
Dissolution medium at 37 ± 0.5°. Use the specified cell size as given in the
individual monograph.
The pump forces the Dissolution
medium upward through the §ow-through cell. The pump has a delivery range
between 240 and 960 mL/h, with standard §ow rates of 4, 8, and 16 mL/min. It must
deliver a constant flow (±5% of the nominal flow rate); the flow profile is
sinusoidal with a pulsation of 120 ± 10 pulses/min. A pump without pulsation
may also be used. Dissolution test procedures using a flow-through cell must be
characterized with respect to rate and any pulsation.
The flow-through cell, of
transparent and inert material, is mounted vertically with a filter system
(specified in the individual monograph) that prevents escape of undissolved
particles from the top of the cell; standard cell diameters are 12 and 22.6 mm;
the bottom cone is usually filled with small glass beads of about 1-mm diameter
with one bead of about 5 mm, positioned at the apex to protect the fluid entry
tube; and a tablet holder is available for positioning of special dosage forms,
e.g., inlay tablets. The cell is immersed in a water bath, and the temperature
is maintained at 37 ± 0.5°.
