Dissolution Apparatus

USP Type Dissolution Apparatus & Use:

Type	Name	Used For
Apparatus I	Basket	Tablets
Apparatus II	Paddle	Tablets. capsules modified drug products
Apparatus III	Reciprocating cylinder	Extended-release drug products.
Apparatus IV	Flow-through cell	Drug products containing low-water-soluble drug
Apparatus V	Paddle over disk	Transdermal drug products.
Apparatus VI	Cylinder	Transdermal drug products.
Apparatus VII	Reciprocating disk	Extended-release drug products
Apparatus VIII	(Non-USP-NF)	Extended-release drug products (beads).
Apparatus IX	(Non-USP-NF)	Ointments, creams, transdermal drug products.

Read about Dissolution, Dissolution Method

Types of dissolution apparatus

1. Drug Dissolution Apparatus-I USP: Rotating Basket
Apparatus I: Basket type (USP Dissolution apparatus 1)

• A cylindrical basket is held by a motor shaft in the rotating basket apparatus (Apparatus I). The sample is held in the basket, which rotates inside a round flask containing the dissolving medium.
• The entire flask is immersed in a constant-temperature bath set at 37°C. The basket’s rotational speed and position must match specified specifications outlined in the current USP.
• General rotating speed for the basket method is 100 rpm.
• To ensure that these mechanical and operating requirements are met, dissolution calibration standards are provided.
• For Chemical Calibration: Prednisone tablets are used.
• Apparatus I is mainly used for capsules and for dosage forms that tend to float or disintegrate slowly.
   

• Two basket attachment designs: On the left is the O-ring design and on the right is the three-pronged USP Apparatus 1 design.

2. Drug Dissolution Apparatus II USP: Paddle Type ,USP Apparatus 2 (Paddle Apparatus)

• The paddle apparatus (USP Apparatus II) comprises of a special, coated paddle that reduces turbulence due to stirring. The paddle is attached vertically to a adjustable-speed motor that rotates at a controlled speed.
• The tablet or capsule is placed in a dissolution flask with a round bottom to reduce turbulence in the dissolution media. Similar to the rotating-basket approach, the apparatus is placed in a constant-temperature water hall (or dissolution bath) maintained at 37°C.
• The position and alignment of the paddle are detailed in the USP. Improper alignment may extremely affect the dissolution outcomes with some drug products.
• The same set of dissolution calibration standards is used to check the equipment before tests are run. The most common operating speed for Apparatus II is 50 rpm for solid oral dosage forms and 25 rpm for suspensions.
• Apparatus II is generally preferred for tablets.
• A sinker, such as a few turns of platinum wire may be used to avoid a capsule or tablet from floating.
• A sinker can also be used for film-coated (MR) tablets that stick or adhere to the vessel walls or help to locate the tablet or capsule under the paddle. The sinker should be such that it does not modify the dissolution characteristics of the dosage form.

•  USP paddle apparatus 2

3. Drug Dissolution Apparatus III USP: Reciprocating cylinder, Apparatus 3 (Reciprocating Cylinder)

• To represent the gastrointestinal tract, a reciprocating cylinder was created mainly for controlled release Tablets or Capsules.
• A set of cylindrical, flat-bottomed glass jars, a set of glass reciprocating cylinders with inert fittings, and a screen at the top and bottom of the cylinders make up the apparatus.

• Because it allows the product to be subjected to varied dissolution media and agitation rates in a single run, USP Apparatus 3 (reciprocating cylinder) is a very adaptable instrument for the in vitro assessment of release properties of solid oral dosage forms.

Brief on Instruments:

1. Vessel: Set of cylindrical flat bottom glass vessels, Set of reciprocating cylinders, stainless steel fittings.

2. Agitation type: Reciprocating (Upward & downward)

3. The cylindrical vessel moves through a distance : 9.9 to 10.1 cm

4. Volume of dissolution medium: 200-250ml

5. Water bath: Maintain at 37±0.5°C

• The dosage form is placed in a cylinder
• USE: Tablets, beads, controlled and extended-release formulations.

Reciprocating cylinder apparatus: (a) Internal cylinder and its top and bottom caps (b) illustration of the internal cylinder coupled to the rod inside the external cylinder (vessel).

4. Drug Dissolution Apparatus IV USP: Flow-through cell, Apparatus 4 (Flow-Through Cell)

• Flow-through (USP Dissolution Apparatus 4) cells are both open and closed-type systems.

Open system:

• Every 30 to 60 minutes, a fresh medium was pumped through the cell and fraction in the open system. As a result, the fraction volume is large. This technique is useful when dealing with drugs that are poorly soluble or when a pH shift is required.

Closed system:

• In a closed system, the medium is circulated through the circle but without the usage of fresh medium.
• When a drug product has a very low strength, especially when performed in low volume, this approach is used. Every hour, the pump delivers between 240 and 960 ml.

Flow-through cell (FTC) Procedure:

• For this, Maintain a dissolution medium at 37 ± 0.5 C°.
• On top of the beads, place 1 dosage form unit through the bottom of the cell.
• Then collect the solution by fractions at each of the times as specified and perform the analysis as given in the individual monograph.

Brief on Flow-through cell (USP Dissolution Apparatus 4):

1.Reservoir: For dissolution medium

2.Pump: Forces dissolution medium through the cell (upward direction)

3.Flow rate: 10-100ml/min Laminar flow is maintained Centrifugal pumps are not recommended

4.Water bath: Maintained at 37± 0.5°C

• Useful for: Low solubility drugs, Micro particulates, Implants, Suppositories, Controlled release formulations

Advantages and disadvantages of the flowthrough dissolution apparatus (USP Dissolution Apparatus 4)

• Advantages:
  • Characteristics of laminar flow over a wide range of solvent flow rates
  • Infinite sink appropriate for low solubility drugs
  • Differential rather than cumulative time profile of dissolved drug concentration Differential rather than cumulative time profile of dissolved drug concentrations
  • Dwell time of dosage form in medium is limited, reducing the danger of drug degradation
  • pH modification of dissolution medium is simple and easy.
  • Samples for analysis are easy to collect without changing the dissolved drug concentration

• Disadvantages:
  • Large volumes of media essential to maintain flow rate
  • Risk of blockage of filters
  • Validation of flow rate during testing is tough.

5. Drug Dissolution Apparatus V USP: Paddle over disk

• Use the paddle and vessel assembly from Apparatus 2, but add a stainless-steel disc assembly to hold the transdermal system in place at the bottom of the vessel.
• Other suitable devices may be utilised as long as they do not sorb, react, or interfere with the specimen under test.
• The disk assembly for holding the transdermal system is designed to minimize any “dead” volume between the disk assembly and the bottom of the vessel, the disk assembly holds the system flat and is positioned such that the release surface is parallel with the bottom of the paddle blade, the vessel may be covered during the test to minimize evaporation.
• Useful for: Transdermal patches
• Standard volume: 900 ml.

Brief on USP Apparatus V: Paddle over disk

1. Vessel & Shaft:  Same as paddle apparatus
2. Rotation Speed:  25-50 rpm
3. Sample holder: disk assembly that holds the product in such a way that release surface is parallel with the paddle blade
4. Distance: 25 ± 2 mm, Samples are drawn between surface of the medium & the top of the paddle blade
5. Temperature: 32 ± 0.5°C

• USE: Transdermal products, emulsions.

6.Drug Dissolution Apparatus VI USP: Cylinder, USP Apparatus 6 (Cylinder)

• Use the vessel assembly as mentioned in Dissolution 〈711〉, Apparatus, Apparatus 1, except substitute the basket and shaft with a stainless-steel cylinder stirring element with the specifications shown in below Figure.
• The distance between the inside bottom of the vessel and the cylinder is maintained at 25 ± 2 mm during the test.

Brief on USP Apparatus VI :

1. Vessel:  Same as basket apparatus
2. Shaft & Cylinder:  Stainless steel
3. Sample: Mounted to cuprophan (inner porous cellulosic material) an entire system has adhered to the cylinder. The dosage unit is placed in a cylinder and released from side out.
4. Rotation Speed: 25-50 rpm
5. Water-bath: maintained at 32±0.5°C

• USE: Mainly transdermal products

7. Drug Dissolution Apparatus VII USP: Reciprocating disk or Reciprocating Holder, USP Apparatus 7 (Reciprocating Holder)

• A reciprocating holder is another name for a reciprocating cylinder. To reciprocate the system vertically, it consists of a volumetrically calibrated and tared solution, a motor, and drives assembly.
• The solution containers are partially immersed in a suitable water bath, with a temperature of 32 0.5 °C for the containers.

USP Apparatus 7, reciprocating holder (created with BioRender.com)

• Brief on USP Apparatus VI

1. Vessel: A set of cylindrical vessels connected to each other Volume of dissolution medium 50-200 ml
2. Shaft
3. Holder: Spring holder/ Reciprocating disk/Teflon cylinder/ Acrylic rod
4. Sample: Placed on holders
5. Agitation: Reciprocating frequency 30 cycle/sec
6. Water bath: Maintained at 32±0.5°C

• USE: Controlled release dosage form, non-disintegrating oral formulations.

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References:

https://www.scielo.br/j/bjps/a/Yf9HcgYnGfNv6q8x4cG7tLN/?lang=en#

https://www.sotax.com/dissolution_testing/usp4_dissolution_testing

https://www.researchgate.net/profile/Mithun-Bhowmick-2/publication/317179626/figure/download/fig15/AS:500003161296903@1496221451677/Paddle-over-Disc-USP-apparatus-V-b-The-Cylinder-modified-USP-Basket-USP-apparatus-VI.png