The content below discusses two delivery methods for HBC, the equations associated with each model and questions for review.

Patch Delivery: Model as Two Semi-Infinite Walls

The model of two semi-infinite walls suggests that the patch starts (t=0) with a uniform mass density Phpi and the skin starts with an initial mass density of zero. As time increases, eq 1 shows the rate of mass flux at the interface, which is appropriate both from the patch to the skin. Eq 2 shows that there is a conservation of mass flux. An important constant is the partition coefficient which, as shown in eq 3, determines how much mass can move from the patch to the skin. The dosage of nicotine from the patch can be calculated from eq 4.

Study Questions

1. Either by finding the appropriate data or by good, justified assumptions, determine the dosage for a hormone patch over the timeframe that it is typically applied.
2. Compare these numbers with the approximate concentration of hormones in the body. The most important results are the comparisons. For example, how would an increased or decreased Kp affect the results? What about Dhs? What physiological reasons could affect these parameters?

Pill Delivery: Model as A Dissolving Sphere

The model of the dissolving sphere, or surface reaction, of drug with a moving boundary condition is the best model here. Pills contain binders which allows for kinetic dispersion. Usually these binders are lactose, sucrose, t=starch or cellulose based which allows them to be dissolved by enzymes and acids in the stomach. Eq 1 is a general mass balance for a sphere with a moving boundary. You will also need to use Fick’s Rate Equation (FRE) and the Equation of Continuity (EOC). Make sure you are consistent in either mass or mole units. Eq 2 sets the mass flux equal to the mass loss from eq 1 when r = R. Solve for t = f(R)

Study Questions

1. Either by finding the appropriate data or by good, justified assumptions, determine the dosage for pill over the timeframe that it is typically used (most pills are every 24 hours).
2. Compare these numbers with the approximate concentration of hormones in the body. The most important results are the comparisons. For example, how would the size of the pill or efficiency of the binder affect the mass release over time.

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