Figure 12.7 (a) An apparatus for the examination of the release of a steroid from a cream formulation: the cream is placed in a Teflon receptacle and covered with a membrane impregnated with isopropyl myristate, and the concentration of fluocinonide is monitored in the bulk isopropyl myristate layer. (b) Release in vitro compared with results of vasoconstrictor tests on four formulations.

Modified from reference 5.

total drug loading and mean particle size can be illustrated, in this case with terconazole.7

Using a rotating bottle apparatus, release of glyceryl trinitrate from Deponit transdermal patches gives the results shown in Fig. 12.10.8 The influence of temperature and pH on release was examined using the same technique, the results confirming that release is essentially determined by the diffusion of drug in the adhesive layer of the product (see section 9.5) but is clearly proportional to surface area, as

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