Biological membranes drug effects

Nakanishi, K., et al. 1990. Effect of cyclodextrins on biological membrane. I. Effect of cyclodextrins on the absorption of a non-absorbable drug from rat small intestine and rectum. Chem Pharm Bull 38 1684. 

Chisty MNA, Bellantone RA, Taft DR, Plakogiannis FM. In vitro evaluation of the release of albuterol sulfate from polymer gels effect of fatty acids on drug transport across biological membranes. Drug Dev Ind Pharm 2002 28(10) 1221—1229. 

This chapter describes some of the properties of solids that affect transport across phases and membranes, with an emphasis on biological membranes. Four aspects are addressed. They include a comparison of crystalline and amorphous forms of the drug, transitions between phases, polymorphism, and hydration. With respect to transport, the major effect of each of these properties is on the apparent solubility, which then affects dissolution and consequently transport. There is often an opposite effect on the stability of the material. Generally, highly crystalline substances are more stable but have lower free energy, solubility, and dissolution characteristics than less crystalline substances. In some situations, this lower solubility and consequent dissolution rate will result in reduced bioavailability. 

Throughout the body, biologic membranes act as barriers that permit some substances to pass freely, while others pass through with difficulty or not at all. This differential separation serves an obvious protective effect by not allowing certain substances to enter the body or by limiting the distribution of the substance within the body. In effect, the body is separated into various compartments by these membranes. In the case of pharmacotherapeutics, there is often the need for the drug to cross one or more of these membrane barriers to reach the target site. 

In this context, Berry [277] studied the enzyme reaction using Monte Carlo simulations in 2-dimensional lattices with varying obstacle densities as models of biological membranes. That author found that the fractal characteristics of the kinetics are increasingly pronounced as obstacle density and initial concentration increase. In addition, the rate constant controlling the rate of the complex formation was found to be, in essence, a time-dependent coefficient since segregation effects arise due to the fractal structure of the reaction medium. In a similar vein, Fuite et al. [278] proposed that the fractal structure of the liver with attendant kinetic properties of drug elimination can explain the unusual... 

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