Dissolution testing of Gels, Topical Creams & Ointments

Dissolution testing of Gels, Topical Creams & Ointments

Dissolution testing of Gels, Topical Creams & Ointments

24 June 2022
The apparatus for dissolution testing must deliver accurate and reproducible data and be easy to use. The Enhancer Cell (also described as the Immersion Cell in the USP) is a cost-effective way to meet these needs. 

Mandatory performance testing for semisolid drug products became official in the August 2013 First Supplement to USP 36 in USP general chapter <1724>. Similar to traditional pharmaceutical products such as tablets, product quality and performance tests for semisolid drug products must ensure their “identity, strength, quality, purity, comparability, and 
performance.”[1] This USP general chapter discusses three types of equipment:

  • • Vertical diffusion cell (sometimes known as the Franz cell)
  • • Immersion cell (also known as the Enhancer Cell)
  • • Cell for USP Apparatus 4

Achieve more reproducible data
Each of the three cell types is a viable solution for quality and performance testing of semisolid dosage forms. However, the Immersion, or Enhancer Cell, offers a distinct advantage over the others and has been shown to deliver more consistent and reliable data. The Enhancer Cell assembly (Figure 1) consists of a polytetrafluoroethylene (PTFE) cell with adjustable volume and a screw cap to retain the skin or artificial membrane. You must control the available surface area because it is critical to achieving reproducible results (2,3,4). Control is accomplished by use of a “washer” with a defined opening of 4.0, 2.0, or 0.5 cm2. The cell body is designed to be adjustable to enable control of the volume of the reservoir within the cell body. The variable depth allows you to test semisolids, solutions, suspensions, or emulsions.A membrane separates the dissolution media from the sample. The membrane should minimize the resistance to drug transport and should therefore be highly porous and of minimal thickness, and it should not bind with the active pharmaceutical ingredient (API). The proper membrane for your product should be chosen based on these characteristics.

Save time and expense with this easy-to-use apparatus
While data integrity is of utmost importance, the biggest advantage of the Enhancer Cell may be its ease of use. You can use the assembly with any dissolution apparatus configured for USP 2 (paddles); these are universal to most laboratories and thus save the expense of a dedicated instrument (5). This familiar equipment shortens the learning curve and makes it possible to bring data online much faster (6). In addition, you can use the Enhancer Cell in vessels that range from 200 mL up to conventional 1-liter volumes. Regardless of volume, the setup is easily automated for sampling and analysis with readily available systems.

Because the Enhancer Cell is made of PTFE, it is inert and will not interact with the formulations in the cell. You avoid the problem with breakage, which is common with most glass diffusion cells. Unlike the Franz cell, the donor compartment of the Enhancer Cell that contains the  formulation is temperature-controlled within the vessel. In summary, the Enhancer Cell solution provides the laboratory with a proven robust technology that is used on a dissolution apparatus that is already familiar to the laboratory staff. The immersion of the Enhancer Cell into the
temperature controlled environment provides necessary temperature stability to the doner compartment. This also seals the ointment or cream from atmospheric exposure that could alter the state of the drug product as it is exposed with the traditional vertical diffusion cell  configuration. Lastly, the thickness of the drug product may be uniformly controlled with the adjustable surface plate.

  1. 1. U.S. Pharmacopoeia 36 / NF 31, 1st Supplement, <1724> Semisolid Drug Products, 2012.
  2. 2. P.P. Sanghvi, C.C. Collins, Drug Development Ind. Pharm. 19 (1993) 1573–1585.
  3. 3. J.L. Zatz, H. Fares, Pharmaceutical Technology. 19 (1) (1995) 52–55.
  4. 4. M. J. Lucero, Carbohydrate Polymers. 2013 January 30; 92(1): 149–56.
  5. 5. P.R. Rege et al. J. Pharmaceutical and Biomedical Analysis. 17 (1998) 1225–1233.
  6. 6. M. Rapedius, J. Blanchard. Pharmaceutical Research, vol. 18 (10), October 2001.

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