Dissolution Testing

Dissolution testing is a critical process in pharmaceutical development. Dissolution testing is a critical quality control and research technique used in the pharmaceutical industry to assess the rate and extent of drug release from a solid dosage form (e.g., tablets, capsules) into a dissolution medium that simulates physiological conditions. The results of dissolution tests are essential for evaluating the performance, bioavailability, and quality of pharmaceutical products.

Types of Dissolution test Apparatus:

There are several types of dissolution testing apparatus used in pharmaceutical and quality control laboratories to assess the release of active pharmaceutical ingredients from solid dosage forms. Some common types include:

USP Apparatus 1 (Basket Dissolution):

This apparatus consists of a wire mesh basket that holds the dosage form and is immersed in the dissolution medium. It is used in pharmaceutical testing to assess the dissolution rate of solid dosage forms, such as tablets and capsules, in various dissolution media.


The procedure for using the Type 1 USP apparatus involves placing the solid dosage form (tablet or capsule) into the basket. Immersing it into the dissolution medium, and allowing it to dissolve while maintaining controlled conditions of temperature and agitation. Samples are periodically withdrawn and analysed, and the dissolution profile is used to assess the drug’s release characteristics.


USP Apparatus 2 (Paddle Dissolution):

The Type 2 Dissolution Test Apparatus is known as the “Paddle Dissolution Apparatus.” Like the Type 1 Basket Dissolution Apparatus, the Type 2 apparatus is used in the pharmaceutical industry to evaluate the dissolution rate of solid dosage forms, such as tablets and capsules, in various dissolution media. However, it uses a different design and method compared to the basket apparatus. It uses a paddle that rotates at a constant speed to agitate the dissolution medium, ensuring uniform mixing.

The Type 2 Dissolution Test Apparatus is often used for drugs and formulations with different dissolution characteristics than those tested using the basket apparatus.

For example, drugs that are sensitive to shear forces. Drugs that have unique release profiles may require the use of the paddle apparatus.

USP Apparatus 3 (Reciprocating Cylinder Dissolution):

Type 3 apparatus is referred to as the “Reciprocating Cylinder” dissolution apparatus. The distinctive feature of the Type 3 apparatus is the reciprocating motion of the pistons. The pistons move up and down, creating a back-and-forth motion within the dissolution medium. This motion is designed to mimic the physiological conditions in the human gastrointestinal tract more closely.

USP Apparatus 4 (Flow-Through Cell Dissolution):

Flow-through cell dissolution is a specialized method used for the dissolution testing of solid dosage forms, particularly those that are poorly soluble or controlled-release formulations.

The flow-through cell dissolution apparatus operates with a continuous flow of dissolution medium through the dosage form. It more closely simulates the physiological conditions in the gastrointestinal tract. It is used for modified-release dosage forms and involves a flow-through cell with a semi-permeable membrane.

USP Apparatus 5 (Paddle Over Disk):

Also known as the “Paddle Over Disk” dissolution apparatus, is used for dissolution testing of solid dosage forms. Particularly those that require more aggressive mixing or have specific release characteristics. This apparatus combines elements of both the paddle and rotating disk methods to provide a unique dissolution profile. This apparatus is used for transdermal and topical products, with a paddle placed over a rotating disk.

USP Apparatus 6 (Rotating Cylinder Dissolution):

Also known as the “Rotating Cylinder Dissolution Apparatus,” is a specialized dissolution testing apparatus. Used for evaluating the dissolution characteristics of solid dosage forms, particularly those with unique geometries or release profiles. This apparatus involves the rotation of a cylinder containing the dosage form in a dissolution medium to measure drug release over time. It uses a rotating cylinder to test extended-release dosage forms.

USP Apparatus 7 (Reciprocating Cylinder Dissolution):

This apparatus is used for controlled release formulation and applies to only small dosages.

The choice of apparatus depends on following: The specific characteristics of the dosage form being tested. The requirements of the dissolution method. Each apparatus simulates different physiological conditions to evaluate drug release accurately.

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