Biological implications of the use of surfactants in medicines: and the biphasic effects of surfactants in biological systems

Abstract

AbstractA survey of the biological effects of surface‐active agents reveals that their affinity for membranes and in particular their ability to penetrate and increase the permeability of membranes is of prime importance. An increase in drug absorption from the gastrointestinal tract, from muscle, from the rectum and from topical preparations is frequently a result of an increase in membrane permeability; the effect of surfactants on enzyme activity can be also the result of changes in organelle permeability or to surfactant‐induced changes in protein conformation. As anionic surfactants and cationic surfactants tend to exhibit too high a degree of toxicity, non‐ionic agents are most commonly used in pharmaceuticals. Experiments to elucidate the mode of action of a range of commercially available non‐ionic surfactants on the increase in drug absorption in model systems employing goldfish (Carassius auratus) are described. Emphasis is placed on the biphasic effects of the surfactants whereby an increase in membrane permeability is observed at low concentrations (frequently below the critical micelle concentration of the surfactant) and a decrease in overall absorption is found at higher concentration. Such biphasic effects are frequently encountered in the literature on surfactant effects in biological systems.