Semisolids
Semisolids
Test Apparatus & Method
There are three different apparatuses for the in vitro determination of drug release from semisolid drug dosage forms:
• Vertical Diffusion Cell (VDC) • Immersion Cell • Flow Through Cell (Apparatus 4) Due to its simplicity and reproducibility, the VDC, or Franz Cell, is typically the apparatus of choice. The VDC comprises two parts: (a) the donor chamber containing the sample to be tested and (b) the receptor chamber containing the receptor medium. The two parts are separated by an inert, highly permeable support membrane that acts as a conduit through which diffusion occurs.
The receptor chamber temperature is usually set to 32°C, to simulate normal skin conditions. At least 6 samples should be taken over a 6-hour period and analysed using HPLC or a similar analytical technique. Results are calculated and expressed as the amount of drug released per unit membrane area (mcg/cm 2 ) vs square root of time. This should yield a straight line. The slope of the line (regression) represents the release rate of the product.
A
B
Sample Holder with ‘Closed’ Cell Top
Schematic of Cell Type C with ‘Open’ Cell Top
59 mm
Annex 1 of the EMA ‘Guideline on quality of transdermal patches’ suggests the use of the VDC for permeation studies on transdermal patches
20 mm
75
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