Drug transfer, physicochemical factor

PHYSICOCHEMICAL FACTORS IN DRUG TRANSFER ACROSS MEMBRANES ... 

Absorption describes the rate and extent to which a drug leaves its site of administration and enters the general circulation. Factors that, therefore, affect absorption include the physicochemical properties of the drug that determine transfer across cell membranes as described earlier formulation or physical state of the drug site of absorption concentration of drug circulation at absorption site and area of absorbing surface. 

Solubility enhancement by use of cyclodextrins is achieved for a number of drug substances, an approach of interest in formulation of drugs for topical, parenteral, and oral use (Stella and Rajewski, 1997 Loftsson and Masson, 2001 Qi and Sikorski, 2001). The solubilizing effect can be extensive even in low concentrations of cyclodextrin. The use of 0.1 M sulfobutyl-ether-P-cyclodextrin increases the solubility of prednisolone acetate and testosterone by a factor of 426 and 2020, respectively (Myrdal and Yalkowsky, 2002). Cyclodextrin encapsulation of a molecule will affect many of its physicochemical properties (Loftsson, 1995). As a result of complexation, solubility, pKa value, spectral properties, and the chemical reactivity of the included substance will change. The cyclodextrins are known to affect molecular orientation and to have an influence on rates and efficiency of electron transfer, excited state proton transfer, and rate of decomposition (Chattopadhyay, 1991 Fox, 1991 Sur et al., 2000). Cyclodextrins can also be used in combination with liposomes a cyclodextrin-liposome entity represents an even more complex environment to the drug molecule (Loukas et al., 1995). 

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