This article explores the different types of dissolution apparatus, with particular emphasis on the 8-stage dissolution system, which stimulates gastrointestinal conditions to provide precise drug release assessments. It discusses key components, operational principles, and the wide-ranging applications of dissolution testing in quality control, pharmaceutical development, and regulatory compliance—highlighting its essential role in ensuring the safety and effectiveness of drug products.

Introduction

Dissolution refers to the process in which a solid drug dissolves into a solvent to form a solution. Dissolution testing evaluates the rate at which active ingredients are released from pharmaceutical dosage forms under standardized conditions.

Dissolution is used in the testing of dosage forms such as buccal and sublingual tablets, chewing gums, soft gelatin capsules, suppositories, transdermal patches, aerosols, and semisolids.

Standardized parameters include temperature, agitation, flow rate, volume, and media composition. The bioavailability and bioequivalence data obtained as a result of dissolution testing can be used as a guiding tool in the drug development and product optimization process.

A dissolution apparatus is an analytical instrument used in the measurement of the dissolution rate of pharmaceutical products under standard conditions, ensuring quality control and regulatory compliance

Types of Dissolution Apparatus

• Basket type (Apparatus 1)

• Paddle type (Apparatus 2)

• Reciprocating cylinder (Apparatus 3)

• Flow-through cell (Apparatus 4)

• Paddle over disc

• Rotating cylinder

• Reciprocating disc

Principle of Dissolution Apparatus
A dissolution apparatus works by simulating the conditions in the gastrointestinal tract to measure the rate and extent of dissolution of a drug from its dosage form.

Components of 8-Stage Dissolution Apparatus

• Vessels: Cylindrical and made of borosilicate glass, with a capacity of 1000 ml.

• Dissolution medium: Provides physiological conditions similar to those in the stomach in which the drug dissolves and is absorbed. Water or another medium containing purified pepsin with a pH less than 6.8 is considered. Commonly used dissolution media include simulated gastric fluid and phosphate buffer solution.
  

• Heating device: A water bath or heating jacket is used to maintain the temperature of the dissolution medium at 36.5–37.5℃.
  

• Paddle: Used for agitation, ensuring constant mixing of the drug and dissolution medium.
  

• Automated sampling and filter system: Some advanced versions include automation for better precision and control.
  

• Rotating mechanism: The shaft ensures the rotation of the paddle at a speed of 50–100 rpm.

• Analysis: Drug release is quantitatively analyzed using High-Performance Liquid Chromatography (HPLC) for precise compound identification, and UV spectrophotometry for rapid detection based on absorbance.

Working of 8-Stage Dissolution Apparatus

The dissolution medium (0.5% hexadecyltrimethylammonium bromide in 0.025 M alkaline borate buffer) is poured into each vessel up to 900 ml at pH 8.

The drug sample is introduced into the vessel using a hypodermic glass needle. 

The paddle is set to rotate at a speed of 75 rpm, a commonly used value within the standard range, and the dissolution is allowed to continue for 60 minutes.

Allow the paddle to rotate at the predetermined speed to ensure proper dissolution of the drug sample in the dissolution medium.

At regular intervals, samples are taken for analysis using HPLC or UV spectroscopy.

Applications of 8-Stage Dissolution Apparatus

• Quality control and quality assurance

• Early-phase drug development

• Assessment of product stability and monitoring of formulation changes over time

• Establishment of in-vivo–in-vitro correlation

Conclusion

The 8-stage dissolution apparatus is an indispensable tool in modern pharmaceutical development. By accurately simulating gastrointestinal conditions, it ensures consistency in drug release profiles, supports regulatory approvals and enhances overall drug safety and efficacy.

References:

1. Dressman, Jennifer B., and Johannes Krämer, eds. Pharmaceutical Dissolution Testing. Boca Raton, FL: Taylor & Francis, 2005.

2. Salve, P. M., S. V. Sonawane, M. B. Patil, and R. K. Surawase. “Dissolution and Dissolution Test Apparatus: A Review.” [Journal Name], 2021. (Note: Please provide the journal name to complete this citation.)

3. Brown, Christopher K., Hiral P. Chokshi, Brian Nickerson, Robert A. Reed, Bruce R. Rohrs, and Pankaj A. Shah. “Dissolution Testing of Poorly Soluble Compounds.” Pharmaceutical Technology 28 (2004): 56–43.

4. Frost, S. M. A. “Introduction to the Validation of a Dissolution Apparatus.” Dissolution Technologies 11, no. 1 (2004): 19–21. https://doi.org/10.14227/DT110104P19.

5. Flair Pharma. “Flair Pharma.” Accessed June 4, 2025. https://flairpharma.com/.

6. Indian Pharmacopoeia Commission. “Dissolution Test.” Accessed June 4, 2025. https://ipc.gov.in/images/pdf/Dissolution_Test-2554700864.pdf.

7. Gianotto, E. A. D. S., R. P. Arantes, M. J. Lara-Filho, A. C. S. Casimiro Filho, and M. M. Fregonezi-Nery. “Dissolution Test for Glibenclamide Tablets.” Química Nova 30 (2007): 1218–1221.

By Tushali Khanna

_MSM/SE