All lengths are ±2 mm).The VDC body (i.e., donor and receptor chambers) usually is made from borosilicate glass, although different materials may be used to manufacture the body and other parts of the VDC assembly.

Vertical diffusion cell–Model B (All dimensions are in mm. The resulting data enable the assessment of different formulations and shelf-life consistency, the evaluation of the impact of process changes, and quality control where they are routinely applied to test for batch-to-batch consistency.Of the three apparatuses specified in USP Chapter <1724>, the VDC is rapidly emerging as the preferred choice because of its simplicity and reproducibility, but the Immersion Cell also remains widely used.

Each VDC cell assembly consists of two chambers (a donor chamber and a receptor chamber) separated by a membrane and held together by a clamp, screw top, or other means (see Typically, amounts of the semisolid sample NLT 200 mg are used. With a jacketed cell design, temperature is maintained using a water circulation system but a more modern, efficient approach is to use a compact heated block (see An Immersion Cell test set-up uses the conventional USP apparatus 2 for oral solid dosage dissolution testing with a smaller volume dissolution vessel: 200 mL rather than the 1 L used in standard testing. All other operational parameters, such as level, vibration, wobble, etc., should be set at the same conditions defined for USP Cut the membrane to an appropriate size.

They are easy to use, have a high degree of patient acceptance and enable the delivery of relatively high concentrations of drug directly to the site of action, substantially reducing the risk of systemic exposure and any associated side effects.

The skin is a commonly used route of administration for pharmaceutical products for both systemic and topical action.

The following points provide some general guidance for receptor medium optimization:The membrane acts as a support for a sample but more specifically provides an The testing procedures and regulatory framework for drug products applied to the skin differs depending on whether they deliver topical or systemic therapies.
Sampling is generally performed over a 4–6 h time period. Stop the stirrer before placing the test sample on the cell. A receptor cell mixer and stirrer magnet are used as the internal stirring mechanism.Before initiating testing, analysts should determine the volume of each VDC with the internal stirring device in place.

substance release) will be included in a new General Chapter <1724> Topical and Transdermal Drug Products: Performance Tests, which will be published in a future issue of PF in 2011. Associated equipment developments make it easier for drug developers to test semisolids efficiently, in line with the new specifications, supporting faster progress towards a successful submission and effective QC.

When the assembly of all donor and receptor chambers and remaining cell components (i.e., disk, alignment ring, and clamp) have been completed, turn on the stirring device, which constitutes the start of the test or time zero.

It is recommended that the cell assembly materials should not significantly react with, adsorb to, or absorb the test product or samples.
A magnetic nonstick (Teflon-coated) stirring bar in the receptor chamber is used as the internal stirring mechanism. Diffusive communication between the semisolid sample and the reservoir takes place through the support membrane.

The appropriate preheated medium may be preloaded in the vessel or can be added after immersion of the immersion cell to start the test. The momentary release rate tracks the depth of penetration of the forming gradient within the semisolid. The test methods and apparatuses specified are designed to produce meaningful and relevant data for these physical forms and generate a release profile for the drug as a function of time. During this procedure it is important to ensure that there are no bubbles beneath the membrane.