Consider the drug patch shown in the figure on the next page. The drug patch consists of

Consider the €œdrug patch€ shown in the figure on the next page. The drug patch consists of a pure drug source mounted on top of a gel diffusion barrier. The gel diffusion barrier has a thickness of 2.0 mm. The gel diffusion barrier is in direct contact with the skin. The cumulative drug release vs. time profile for a 3.0-cm × 3.0-cm square patch at 20°C is also shown below. Other experiments showed that the drug was immediately taken up into the body after exiting the patch. The drug is only slightly soluble in the gel material. The maximum solubility of the drug in the gel diffusion barrier is 0.50 µmole/ cm³, and the solubility of the drug in the gel diffusion barrier is not affected by temperature. 

a. From the data shown below, estimate the effective diffusion coefficient of the drug in the diffusion barrier. 

b. When used on the body, heat transfer raises the temperature of the drug patch to about 35°C. What is the new drug delivery rate (W_A) at this temperature in units of µmole/day? For purposes of this analysis, assume that the gel-like diffusion barrier material approximates the properties of liquid water. 

Transcribed Image Text:

Drug patch Drug reservoir Impermeable barrier -Gel diffusion barrier Skin surface Infected body tissue (sink for drug) 0.20 0.15 0.10 0.05 0.00 10 15 20 25 Time (hours) Drug released (u moles A)